OUTLINES 


OF 


INDUSTRIAL  CHEMISTRY 


A    TEXT-BOOK  FOE  STUDENTS 


BY 


FRANK   HALL   THORP,  PH.D. 

INSTRUCTOR  IN   INDUSTRIAL  CHEMISTRY   IN    THE   MASSACHUSETTS 
INSTITUTE  OF  TECHNOLOGY 


THE  MACMILLAN   COMPANY 

LONDON:  MACMILLAN  &  CO.,  LTD. 

1898 

All  rights  reserved 


COPYRIGHT,  1898, 
BY  THE  MACMILLAN  COMPANY. 


J.  S.  Cashing  &  Co.  —  Berwick  &  Smith 
Norwood  Mass.  U.S.A. 


V 

• 


Eo  tfje  J$lem0t|j  of 
LEWIS  MILLS  NORTON 

DURING    NINE    YEARS    PROFESSOR    OF    INDUSTRIAL    CHEMISTRY 
IN  THE   MASSACHUSETTS   INSTITUTE   OF   TECHNOLOGY 

3Efjts  iSooft  is  BeUtcatrtJ 

IN  TOKEN   OF   WARM   PERSONAL   REGARD   FOR    THE   KINDLY   MAN 

AND   GRATEFUL    APPRECIATION    OF 
THE   HELPFULNESS   AND   INSPIRATION   OF   HIS   TEACHING 

THE  AUTHOR 


PREFACE 


THE  object  of  this  book  is  to  furnish  an  elementary  course  in 
Industrial  Chemistry,  which  may  serve  as  the  ground  work  for 
a  more  extended  course  of  lectures,  if  desired.  The  writer  has 
endeavored  to  describe  briefly,  within  the  limits  of  one  moderate- 
sized  volume,  the  more  important  industrial  chemical  processes,  but 
omitting  matters  of  detail  which  properly  belong  in  the  larger  hand- 
books. Numerous  references  are  made  in  the  text  to  periodicals 
and  journals,  and  to  the  standard  hand-books  and  encyclopaedias 
and  many  special  works,  where  details,  lacking  in  this  book,  may 
be  found.  The  bibliographical  lists  following  each  section  are  not 
complete,  but  only  include  those  works  which  will  usually  be  found 
in  most  chemical  libraries ;  the  references  to  the  journal  literature 
are  merely  those  articles  to  which  the  author's  attention  has  been 
drawn  in  the  preparation  of  class-room  exercises.  The  diagrams 
illustrating  the  text  have,  in  most  cases,  been  drawn  as  simply  as 
possible,  purposely  showing  only  the  essential  features. 

In  the  selection  and  order  of  arrangement  of  the  several  sub- 
jects, the  author  has  necessarily  been  influenced  by  his  work  in 
this  Institute  and  the  requirements  of  his  own  class,  but  it  is 
believed  that  the  book  as  a  whole  will  be  found  applicable  to  the 
work  in  most  institutions  of  learning  where  industrial  chemistry 
is  taught.  The  subject  of  Metallurgy  has  been  entirely  omitted, 
since  there  are  already  several  excellent  brief  text-books  dealing 
with  it  alone,  and  instruction  in  it  is  generally  given  independently 
of  that  relating  to  technical  chemistry.  Likewise  the  important 
subject  of  the  coal-tar  colors  has  been  condensed  into  the  briefest 
possible  outline,  because  this  is  nearly  always  included  in  courses 
in  organic  chemistry,  and  there  are  several  small  manuals  treating 
of  it.  Analytical  processes  have  also  been  omitted  as  foreign  to 
the  intended  scope  and  purpose  of  the  book. 

It  is  assumed  that  students  taking  this  course  are  familiar  with 
the  elements  of  general  chemistry,  both  inorganic  and  organic,  and 
with  the  elements  of  physics. 

vii 


viii  PKEFACE 

In  the  compilation  of  this  work,  free  use  has  been  made  of  many 
of  the  standard  English,  German,  and  French  hand-books  and 
encyclopaedias,  particularly  of  Professor  T.  E.  Thorpe's  Dictionary 
of  Applied  Chemistry,  the  works  of  Professor  Lunge  on  Sulphuric 
Acid  and  Alkali,  and  Coal-tar  and  Ammonia,  Ost's  Technischen 
Cheinie,  and  Dammer's  Handbuch  der  chemischen  Technologic. 

The  following  business  firms  have  courteously  loaned  cuts  and 
drawings  for  the  illustrations :  Curtis  Davis  &  Co.,  Cambridgeport, 
Mass.,  slabbing  machine  and  soap  kettle ;  William  Campbell  &  Sons, 
Cambridgeport,  Mass.,  rendering  tank ;  The  De  La  Vergne  Eef  riger- 
ating  Machine  Co.,  New  York,  refrigerating  machine ;  H.  L.  Dixon, 
Pittsburg,  Pa.,  tank  furnace  for  glass;  United  Gas  Improvement 
Co.,  Philadelphia,  water  gas  plant ;  John  Johnson  &  Co.,  New  York, 
filter  press;  Semet-Solway  Company,  Syracuse,  N.Y.,  coke  oven; 
E.  D.  Wood  &  Co.,  Philadelphia,  Pa.,  Taylor  gas  producer. 

The  writer  wishes  to  acknowledge  his  indebtedness  to  the  fol- 
lowing friends  for  assistance  and  advice  in  the  revision  of  those 
portions  of  the  work  treating  of  their  specialties :  C.  D.  Jenkins, 
State  Gas  Inspector  of  Massachusetts,  Illuminating  Gas ;  A.  D. 
Little,  Consulting  Chemist,  Wood  Pulp  and  Paper ;  J.  W.  Loveland, 
Superintendent  Curtis  Davis  &  Co.,  Soap  Manufacturers,  Soap, 
Candles,  and  Glycerine;  F.  G.  Stantial,  Superintendent  Cochrane 
Chemical  Co.,  Sulphuric,  Hydrochloric,  and  Nitric  Acids;  the  fol- 
lowing members  of  the  instructing  staff  of  the  Massachusetts 
Institute  of  Technology:  Professor  A.  H.  Gill,  Fuels  and  Oils; 
G.  W.  Eolfe,  Starch,  Glucose,  and  Sugar;  S.  C.  Prescott,  Fermen- 
tation Industries ;  J.  W.  Smith,  Textile  Industries. 

Special  thanks  are  due  to  Dr.  W.  E.  Whitney,  of  the  Institute 
of  Technology,  for  much  assistance  in  the  proof-reading,  and  also 
to  Dr.  B.  L.  Eobinson,  of  the  Gray  Herbarium,  Harvard  University, 
for  his  painstaking  revision  of  the  botanical  nomenclature. 

In  the  labor  of  preparation  of  the  book,  the  author  has  also  had 
much  help  from  his  wife,  who  copied  the  entire  manuscript  and  has 
assisted  in  the  reading  of  all  of  the  proof. 

FRANK  H.  THORP. 
BOSTON,  MASS., 
October,  1898. 


TABLE   OF  CONTENTS 


PART  I 


INORGANIC  INDUSTRIES 


INTRODUCTION. 

Objects  of  Industrial  Chemistry  1 

Lixiviation 2 

Levigation       2 

Evaporation 3 

Spontaneous -8 

By  direct  heat       ....  4 

By  steam  heat       ....  6 

In  vacuum 5 

Vacuum  pans     ....  5 

Multiple  effect  systems    .  6 

Yaryan  evaporator  .     .  6 

Distillation 7 

Fractional  condensation    .     .  8 

Coupler's  still 8 

French  column  apparatus  .     .  9 

Coffey  still 9 

Sublimation 10 

Filtration 11 

Bag  niters 11 

Suction  filtration       ....  12 
Pressure  filtration,  by  use  of 

the  filter  press 12 

Centrifugal  filtration     ...  14 

Sand  filters 15 

Crystallization 15 

Calcination 16 

Muffle  furnace 16 

Reverberatory  furnace ...  17 

Revolving  furnace    ....  17 

Shaft  furnace  or  kiln    .     .     .  18 

Refrigeration 18 

Compression  machines      .     .  19 

Absorption  machines    ...  20 

Chilling  by  compressed  air     .  20 


Density 21 

Hydrometers 21 

Pyknometer 23 

WestphaPs  balance  ....  23 

FUELS. 

Solid  fuels 24 

Wood,  peat,  lignite  or  brown 
coal,  bituminous  coal,  an- 
thracite, charcoal,  coke  24-28 

Beehive  coke  oven     ...  28 

By-product  coke  ovens  .     .  29 

Liquid  fuels   .......  30 

Crude  petroleum  and  oil  resi- 
dues   30 

Gaseous  fuels     ..     .     .    .    .     .  30 

Natural  gas      ......  30 

Producer  gas 30 

Siemen's  gas  producer   .     .  31 

Taylor's  gas  producer    .     .  31 

Water  gas 33 

Coal  gas -33 

WATER. 

Hard,  soft,  saline,  alkaline  .     .  35 
Purification  by  chemical  precipi- 
tation        36 

Clark's  process 36 

Other  processes   ....    36-37 

Boiler  scale 37 

Water  for  special  industries .     .  37 


SULPHUR. 

Extraction,  from  ore 
Recovered  sulphur  . 


40 
42 


ix 


TABLE   OF  CONTENTS 


Purification    .... 

Dejardin's  apparatus 
Sulphur  derivatives 

Sulphur  dioxide  . 

Sodium  bisulphite    . 

Calcium  bisulphite   . 

Hyposulphurous  acid 

Sodium  hyposulphite 

Sodium  thiosulphate 


PAGE 

.  42 
.  42 
43-45 
.  43 
.  44 
.  44 
.  44 
.  44 
45 


SULPHURIC  ACID. 
Theories  of  the  formation  of  the 

acid 47 

Sulphur  burners 48 

Pyrites  burners 49 

Lump  ore  burner  ....  50 
"  Fines "  burners      .     .    50-52 

"^•Glover  tower 52 

Lead  chambers 52 

~  Gay-Lussac  tower    ....  54 

Acid  egg 55 

Air-lift  pump  for  acid  ...  56 

Glass  and  platinum  stills  .     .  56 

Cast-iron  stills 58 

Lunge's  plate  tower ....  59 

Barbier's  tower  system      .     .  59 

Fuming  sulphuric  acid      ...  60 

.  SALT. 

Sources  of  salt 61 

Preparation  of  salt 63 

HYDROCHLORIC  ACID  AND  SODIUM  SUL- 
PHATE. 

Salt-cake  furnaces 67 

Open  roaster 67 

Close  roaster 68 

Mactear's  roaster     ....  69 

Coke  tower  for  absorption    .     .  70 

Hargreaves-Robinson  process    .  71 

Sodium  sulphate 72 

SODA  INDUSTRY. 

Leblanc  process 73  • 

Black-ash  or  balling  furnace  .  74 

Lixiviation  of  black-ash    .     .  76 
Carbonation  and  evaporation 

of  tank  liquor    .     .     .     .  77 

Thelen'span 79 


Soda  crystals  or  sal-soda   .     .  79 

Caustic  soda 80 

Loewig's  process  ....  81 

Tank  waste 82 

Methods   of    treating  tank 

waste 83-84 

Ammonia  soda  process     .     .     .  86  < 
Parnell- Simpson  modification 

of  this  process 90 

Cryolite  soda  process  ....  92 

CHLORINE  INDUSTRY. 

Processes  using  manganese    .    96-97 

Dunlop's 96 

Weldon's 96 

Schlossing's 97 

Deacon's  copper  chloride  process    98 

Nitric  acid  processes  for  chlorine  101 
Dunlop's  process  ....  101 

Donald's  process 101 

Sadler- Wilson  process  .     .     .  101 

Magnesia  processes  for  chlorine  102 
Weldon-Pechiney  process  .  102 

Processes  for  recovering  chlorine 
from  ammonia -soda  waste 
liquors  .....'...  103 

Electrolytic  processes  for  chlo- 
rine and  caustic  soda  .  .104 
LeSueur's  process  ....  105 
Carmichael's  process  .  .  .  106 
Greenwood's  process  .  .  .  106 
Holland-Richardson  process  .  106 
Hargreaves-Bird  process  .  .  107 

Hermite  process 107 

Castner's1  process      ....  107 

Hypochlorites 108 

Bleaching  materials      .     .     .  109 

Chlorates  .     .     .  ^ .     .     .     .     -Ill 

Liebig's  process Ill 

Pechiney's  process    .     .     .     .112 
Gall-Montlaur  process  .     .     .113 

NITRIC  ACID. 

Method  of  manufacture  .  .  .114 
Guttmann's  apparatus  .  .  .  116 
Hart's  apparatus  .  .  .*  .  117 

Fuming  nitric  acid 118 

Commercial  nitrates    ,  119-124 


TABLE   OF   CONTENTS 


XI 


PAGE 

AMMONIA. 
Sources  of  ammonia    ....  124 

Gas  liquor  .......  125 

Feldmann's  apparatus  .  .  .  125 
Griineberg-Blum  apparatus  .  .  126 
Ammonium  salts  .  .  .  128-129 

POTASH  INDUSTRY. 
Sources  of  potash  salts     .     .     .  130 
Strassfurt  deposit  of  potash 
salts    ........  132 

Wool  washings    .....  131 

Potassium  compounds      .     135-136 

FERTILIZERS. 

Requisites  of  a  fertilizer  .  .  .  137 
Waste  products  as  source  of  fer- 

tilizer ........  138 

Bones,  blood,  garbage,  etc.    .  138 

Peruvian  and  fossil  guanos  .     .  140 

Phosphate  rocks      .....  140 

Apatite  ........  140 

Phosphorites   ......  141 

Superphosphates      .....  143 

Reverted  phosphate  ....  144 

Phosphatic  slag  ......  145 

Sewage  as  fertilizer      ....  147 

Land  plaster  .......  147 

LIME,     CEMENT,     AND     PLASTER    OF 

PARIS. 
Lime     .........  148 

Properties  of  lime    ....  148 

Limekilns    ......  148 

Hydraulic  lime     .....  150 

Mortar  .......     .     .  151 

Cements    ........  152 

Manufacture  of  cements    154-156 

Cement  kilns    .     .     .     156-158 

Hardening  of  cements  .    .     .  159 

Testing  of  cement    ....  160 

Plaster  of  Paris  ......  163 


Properties  and  composition  of 

...  165 
...  166 
168-169 


Lime  and  lead  glass 
Glass  furnaces 


PAGE 

Glass  pots,  open  and  closed  .  170 

Plate  glass 173 

Window  glass  and  glass  blowing  174 

Crown  glass 175 

Pressed  and  cut  glass  ....  175 

Tempered  glass 175 

Compound  glass 176 

Colored  glass 176 

Enamel 178 

Iridescent  glass  .     .     ...     .178 

s.  Mirrors      ....    ..    .     .  "..     .  178 

CERAMIC  INDUSTRIES. 

Kaolin  or  china  clay    .     .     .     .180 

Fire-clay 180 

Pipe  or  ball  clay 180 

Empirical  and  rational  analyses 

of  clays 182 

Ceramics 182 

Non-porous  ware      .     .     .     .182 
Porcelain  and  stoneware     .  182 

Kilns 184 

Porous  ware 185 

Faience  and  common  pot- 
tery       185 

Majolica 185 

Tiles 185 

Vitrified,  encaustic,   and 
glazed  tiles     .     .     .     .185 

Glazes 186 

Engobe,      enamel,      and 

transparent  glazes   .     .  186 
Crazing  of  glaze      .     .     .  187 

Terra  cotta 187 

Bricks 187 

PIGMENTS. 

White  pigments .     .     .     .     190-198 

White  lead      190 

Dutch  process 190 

Chamber  process  .  .  .  .192 
The'nard's  process  .  .  .  193 
Milner's  process  ....  194 
Kremnitz  process .  .  .  .194 
Electrolytic  process  .  .  .195 
White  lead  substitutes  .  .  .196 
Sublimed  white  lead  .  .  .196 
Lead  sulphite 196 


X-ll 


TABLE  OF  CONTENTS 


PAGE 

Pattinson's  white  lead    .     .196 

White  zinc 197 

Barytes 197 

Gypsum,  terra  alba  ....  197 

Whiting 198 

China  clay 198 

Blue  pigments     ....      198-202 

Ultramarine 198 

Prussian  or  Berlin  blue      .     .  200 
Smalt  and  cobalt  blues      .     .  201 

Copper  blues 202 

Indigo 202 

Green  pigments 202 

Ultramarine  green    ....  202 

Brunswick  green 202 

Chrome  and  Guignet's  greens  203 

Copper  greens 204 

Malachite,  verdigris  .     .     .  204 

Copper-arsenic  greens  .     .     .  204 

Scheele's  and  Paris  greens  .  205 

Terra  verde 105 

Yellow  pigments 205 

Chrome  yellows 205 

Yellow  ochre  and  Sienna  .     .  207 

Cadmium  yellow 207 

Orpiment 207 

Litharge 207 

Gamboge 208 

Indian  yellow  or  purree    .     .  208 

Orange  pigments 208 

Orange  mineral 208 

Chrome  orange 208 

Antimony  orange     ....  208 

Red  pigments  ....  209-212 
Bed  lead,  chrome  red  .  .  .  209 
Red  ochre,  vermilion  .  .  .210 
Iron  reds,  Venetian  red,  etc.  210 
Realgar,  antimony  red  .  .  .  212 
Carmine  and  "lakes"  .  .  .  212 

Brown  pigments 213 

Umber,  Vandyke  brown,  and 
sepia 213 

Black  pigments 213 

Lampblack,  ivory  -  black, 
bone-black,  charcoal,  graph- 
ite, manganese  blacks,  etc. 


BROMINE. 

Methods  of  extraction 
"  Solidified  bromine  " 
Bromides    . 


PAGE 

215 
217 

218 


IODINE. 

Extraction  from  kelp  and  varec  218 
Extraction    from    the    mother- 
liquors  of  sodium  nitrate    .219 
Potassium  iodide 220 

PHOSPHORUS. 

Preparation  from  bone-ash  .     .  221 
Preparation  from  mineral  phos- 
phates       222 

Yellow  and  amorphous  phos- 
phorus      223 

Matches     .     ."..'....     .     .     .  224 

BORIC  ACID. 

Sources  and  preparation  .     .     .  225 
Borax 226 

ARSENIC  COMPOUNDS. 
Arsenious  acid,  white  arsenic    .  229 

Arsenic  acid 229 

Sodium  arsenate 230 

Sodium  arsenite  .  .     .  230 


WATER-GLASS 


230 


PEROXIDES. 

Barium,  sodium,  and  hydrogen 
peroxides 231 

OXYGE-N. 

From  potassium  chlorate  .     .     .  283 

Deville's  process 234 

Boussingault's  process      .     .     .  234 

Brin's  modification  .     .    .     .234 

Tessie  du  Motay's  process     .     .  235 

Linde"  refrigeration  process  .     .  236 

SULPHATES. 

Ferrous  sulphate,  green  vitriol .  237- 
Copper  sulphate,  blue  vitriol  .  239 
Zinc  sulphate,  white  vitriol  .  .  240 
Aluminum  sulphate  ....  240 
From  clay  and  bauxite  .  .  241 


TABLE   OF   CONTENTS 


xin 


Bayer's  method  for  pure  alu- 
mina   242 

Aluminum  sulphate  from  cry- 
olite     243 

Alum          244 

Preparation  from  alunite  .     .  244 
Preparation  from  clay,  cryo- 
lite, or  bauxite      ....  245 
"Neutral  alum"      .     .     .     .246 
Potassium,     ammonium,    so- 
dium,   iron,    and    chrome 
alums.  .  246 


CYANIDES. 

Bunsen  and  Playfair  process     .  247 

Ammonium  sulphocyanide   .     .  248 

Gelis'  process 248 


PAGE 

Recovery  from  the  spent  ox- 
ides of  the  illuminating  gas 

purification 248 

Potassium  ferrocyanide  .  .  .  249 
Potassium  ferricyanide  .  .  .  250 
Barium  sulphocyanide  .  .  .  250 
Potassium  cyanide 251 

CARBON  BISULPHIDE 253 

CARBON  TETRACHLORIDE     .     .     .  255 

MANGANATES  AND  PERMANGA- 
NATES. 

Sodium  and  potassium  manga- 
nates 255 

Sodium  and  potassium  perman- 
ganates   255 


PART  II 

ORGANIC  INDUSTRIES 


DESTRUCTIVE     DISTILLATION     OF 

WOOD. 

Pyroligneous  acid 257 

Methyl  alcohol 259 

Acetone 260 

Acetic  acid 261 

Acetates 262 

Wood-tar 263 

DESTRUCTIVE     DISTILLATION     OF 
BONES. 

Bone  oil 265 

Bone-black 265 

ILLUMINATING  GAS. 
Carburetted  water  gas  .    .    .    .  266 

Coal  gas 268 

Purification  of  gas 274 

Oil  gas 276 

Acetylene 277 

Air  gas 277 


COAL  TAR. 
Properties  of  tar 


278 


PAGE 

Distillation  of  tar 279 

First  runnings 282 

Light  oil 282 

Naphtha 282 

Carbolic  oil 283 

Creosote  oil 283 

Naphthalene 284 

Anthracene  oil 284 

Pitch 285 

^MINERAL  OILS. 

Petroleum  industry. 
Distribution    and    origin    of 

petroleum 285 

Oil-well  drilling     .    .    .    .     .  287 

Crude  petroleum 290 

Refining" 290 

"  Cracking  "  of  crude  oil    .    .  292 
Purification  of  distillates    .    .  293 

Paraffine  oils 294 

"Neutral"  oils.    ....  294 

Reduced  oils 295 

Vaseline 295 

Russian  petroleums   ....  295 


XIV 


TABLE  OF   CONTENTS 


Oil  testing 295 

Use  of  petroleum  oils  to  pre- 
vent spontaneous  combus- 
tion of  animal  and  vegetable 

oils 297 

Shale  oil  industry. 

Distillation     of     bituminous 
shale      .........  298 

Ozokerite. 

Purification  of  mineral  wax    .  299 
Asphalt. 

Occurrence  and  uses  of  min- 
eral pitch 299 

VEGETABLE    AND    ANIMAL    OILS, 
FATS  AND  WAXES. 

Properties  of  the  fatty  oils    .    .301 

Hydrolysis  of  fats 303 

Occurrence    and    extraction  of 

vegetable  oils 304 

Occurrence    and    extraction  of 
animal  oils    .    .     .    «   ".  -  .    .  305 

Testing  of  fatty  oils 306 

Classification  of  oils 307 

Vegetable  drying  oils  .  .  .  308 
Vegetable  semi-drying  oils  .  310 
Vegetable  non-drying  oils  .  .  313 
Marine  animal  oils  ....  314 
Terrestrial  animal  oils  .  .  .315 
Solid  vegetable  fats  ....  316 

Solid  animal  fats 317 

Waxes. 

Liquid  waxes 318 

Solid  animal  waxes  ....  319 
Solid  vegetable  wax  ....  320 

SOAP. 

Saponification 321 

Cold  process  soap 324 

Boiled  soaps 324 

Yellow  (rosin)  soaps      .    .    .  325 

White  soaps .    .  ' 325 

Toilet  soaps 327 

Milled  soaps 328 

Kemelted  soaps 328 

Transparent  soap  ....  328 
Scouring  soaps 328 


CANDLES. 
Dipped,   poured,   and  moulded 

candles 329 

Saponification  of  fats  for  candle 
stock 330 

GLYCERINE. 

Van  Ruymbeke  process  for  the 
recovery  of  glycerine  from 
spent  soap  lyes  .  «  .  .  .  332 

Glycerine  from  candle  stock  .    .  333 

Glatz  process  for  recovery  of 
glycerine  from  soap  lyes  .  .  333 

Properties  and  uses  of  glycerine  334 

ESSENTIAL  OILS. 

Properties  and  methods  of  ex- 
traction .  '.  ...  .  -  .  .  335 

Characteristics  of  the  individual 
oils 336-340 

RESINS  AND  GUMS. 

Resins 341-345 

Varnishes. 

Spirit,  turpentine,  and  lin- 
seed oil  varnishes    .    .    .  345 
Oleo-resins. 

Balsams 346 

Caoutchouc  (India  rubber)    .     .  346 

Guttapercha 350 

Gum  resins. 
Properties  of  individual  gum 

resins 350-351 

Gums. 
Properties  of  the  gums  .    .    .  351 

STARCH,  DEXTRIN,  AND  GLUCOSE. 
Occurrence    and   properties   of 

starch 353 

Corn  starch 354 

Wheat  starch 358 

Potato  starch 359 

Rice  starch 360 

Sago 361 

Arrowroot 361 

Cassava    ..•.-.•.".    .    .  362 
Dextrin. 

Manufacture  and  properties  of 
dextrin  and  of  British  gum  363 


TABLE  OF   CONTENTS 


xv 


PAGE 

Glucose. 

Dextrose 364 

Lsevulose 364 

Commercial  glucose  ....  364 

Conversion 364 

Neutralization 366 

Bone-char  filtration    .    .     .  367 

CANE  SUGAR. 
Occurrence    and    properties   of 

cane  sugar 370 

Raw  sugar  manufactured  from 

sugar  cane 372 

Raw  sugar  manufactured  from 

sugar  beets 376 

M  Sugar  refining 378-382 

FERMENTATION  INDUSTRIES. 
Fermentation. 

Organized  ferments    ....  384 

Mould  growths 385 

Bacteria 385 

Yeast  plants 386 

Wine. 

Composition  of  grape  juice  .  389 
Extraction  of  the  must  .  .  .390 
Fermentation  of  the  must .  .  390 
Preservation  of  wine ....  392 

Champagne 393 

Other  wines 393 

Brewing. 

Malting 394 

Steeping,     couching,     and 

flooring 395 

Pneumatic  malting     .     .     .  396 

Mashing 398 

Infusion  method     ....  398 

Decoction  method  ....  399 

Boiling  of  the  wort    ....  400 

Hops 400 

Cooling  the  hot  wort ....  401 

Fermenting 401 

Pitching 401 

Bottom  fermentation  .     .     .  402 
Top  fermentation   ....  403 

Extract  in  beer 403 

Bottling  or  barrelling  .  .  .  403 
Brewed  liquors 404 


Distilled  liquors. 

Alcohol,  manufacture    .    .    .  405 
Distillation,  of  the  mash     .  407 
Purification    and    rectifica- 
tion of  raw  spirit     .     .    .  408 

Silent  spirit 409 

Methylated  spirit  ....  409 

Fusel  oil 410 

Whiskey 410 

Gin  .     .    .    ...  ./>    ;    .    .    .411 

Brandy     .  ;.  ..>..>.  .* ..!.    .  411 

Rum 411 

Liqueurs  and  arrack .    .     .    .411 
Vinegar. 

Orleans  process 412 

Quick  vinegar  process    .     .    .  413 
Cider,  wine,  and  malt  vine- 
gars   414 

Lactic  fermentation 415 

Lactic  acid    .  .  416 


EXPLOSIVES. 

Characteristic  properties  of  ex- 
plosives      417 

Gunpowder 418 

Pebble  and  prismatic  powders  421 
Brown  or  cocoa  powder  .  .  422 
Mining  powders 422 

Nitrocellulose  .    .    .<....    .    .423 

Guncotton 423 

Pyroxyline 425 

Smokeless  powders    .    .   425,  430 

Nitroglycerine 425 

Preparation  and  purification  .  426 

Dynamite 428 

Mica  powder     ......  429 

Forcite 430 

Blasting  gelatine 430 

Gelatine  dynamite  and  cordite  430 

Picrates 431 

Melinite 431' 

Fulminates 431 

Sprengel  explosives 432 

Roburite,  romite,  bellite,  and 
ammonite 432 

Lime  cartridges 432 


XVI 


TABLE   OF  CONTENTS 


TEXTILE  INDUSTRIES. 
Fibres. 

Vegetable  fibres 434 

Cotton 434 

Linen 435 

Hemp 436 

Jute 437 

China  grass  (ramie)   .    .     .  437 

Esparto 437 

Manilla,    sisal,    and    sunn 

hemp 437 

Animal  fibres 438 

Silk 438 

Wool 442 

Wool  scouring  and  recov- 
ery of  wool  grease    .    .  444 
Bleaching. 

Cotton  bleaching 446 

Market,  madder,  and  Tur- 
key-red bleach    ....  448 
Mather-Thompson  process  .  452 
Hermite  bleaching  process  .  453 
Hydrogen  peroxide  and  po- 
tassium permanganate  as 
cotton  bleaches  ....  453 

Linen  bleaching 453 

Irish  process 453 

Jute  bleaching 454 

Hemp  bleaching 454 

Wool  bleaching 455 

Stretching  of  yarn ....  455 
"Crabbing"  of  union  goods  455 

Stoving 456 

Hydrogen  peroxide     .    .    .  456 

Silk  bleaching 457 

Mordants. 

Action  of  mordants  ....  457 
Metallic  mordants  .  .  458-462 
Organic  mordants .  .  .  462-466 

Tannins 463 

Coloring  matters. 

Natural  dyestuffs 466 

Indigo 466 

Logwood 467 

Bed  woods 468 

Madder 468 

Archil  .  469 


PAGE 

Litmus,  cochineal  ....  469 
Lac  dye,  kermes  ....  469 
Fustic,  quercitron  ....  470 

Persian  berries 470 

Curcuma,  annatto  ....  470 
Artificial  dyestuffs    ...    .470 

Rosaniline  dyes 471 

Safranines  and  indulines     .  472 

Oxazines 472 

Thionines  .....    .     .    .     .  473 

Aniline  black 473 

Nitro  dyes 473 

Nitroso  dyes 473 

Phthaleins 473 

Eosins    .......  474 

Bosolic  acids 474 

Amidoazo  dyes 474 

Amidoazosulphonic  acids    .  475 

Oxyazo  dyes 475 

Quinoline  and  acridine  dyes  477 

Anthracene  dyes    .     .     .     .477 

Artificial  indigo      ....  479 

Dyeing. 

Properties  of  dyestuffs  .    .    .479 

Theory  of  dyeing 480 

Methods  of  dyeing     .    .    .     .481 

Direct  dyes 482 

Basic  dyes 483 

Acid  dyes 484 

Mordant  dyes 486 

Colors    developed    on    the 

fibre 489 

Indigo 489 

Aniline  black      .    .    .    .491 
Azo  dyes    developed    on 

the  fibre 492 

Mineral  dyes 492 

Textile  printing. 

Block  printing 494 

Machine  printing 495 

Color  mixing 496 

Styles 497 

Pigment  style 497 

Steam  style 497 

Madder  or  dyeing  style  .     .  498 

Oxidation  style 498 

Discharge  style 498 


TABLE   OF  CONTENTS 


xvii 


Resist  style 499 

Wool  printing 499 

Silk  printing 499 

PAPER. 

Materials  for  paper 501 

Wood  pulp    .     .     .     .    .    .    .  502 

Mechanical  pulp     ....  502 

Chemical  pulp 502 

Soda  process 502 

Sulphite  process ....  503 
Sulphate  process     .     .     .  506 

Rags 508 

Esparto 508 

Jute 509 

Bleaching  paper  pulp    ....  509 

Paper  making 509 

Sizing 510 

Hand-made  paper      .     .     .    .511 

Cylinder  machine 511 

Fourdrinier  machine .     .     .     .  511 

Printing  paper   ......  512 

Wrapping  paper     ....  512 

Writing  paper 512 

Blotting  paper 512 

Parchment  paper    .     .     .     .513 
Willisden  paper      ....  513 

LEATHER. 

Structure  of  skin 514 

Classification  of  pelts    .     .     .    .515 

Preparation  of  the  skins    .     .     .  516 

Depilation  processes  ....  516 

Liming 516 


PAGK 

Sweating 517 

Beaming 517 

Bating 517 

Tanning  processes 618 

With  tannin.     .     .     ...    .  618 

Sole  leather   .     .    .    .     .     .519 

Upper  leather     .    .    .     .     .  520 

Currying  .  .  .  .  .  .620 

Colored  leather 520 

Split  leathers 520 

Tawing  (mineral  tannage)  .  521 
Combination  tannage .  .  .521 
Chrome  tannage  ....  521 

Oil  tanning 522 

Degras 523 

Sod-oil 523 

Morocco  leather  ....  523 

Russia  leather 523 

Patent  leather 523 

Parchment 524 

Artificial  leather  .  .  .  .524 

Theory  of  tanning     ....  524 

GLUE. 

Sources  of  glue 525 

Constituents  of  glue      ....  525 
Preparation  of  glue    .     .     .     .525 

Hide  glue 525 

Bone  glue 527 

Fish  glue 527 

Liquid  glue 527 

Gelatine 627 

Isinglass 528 


GENERAL   REFERENCES    ON    INDUSTRIAL 
CHEMISTRY 

Chimie  Industrielle.    A.  Payen.     Paris,  1867. 
Grundriss  der  chemischen  Technologie.     H.  Post. 

Abriss  der  chemischen  Technologie.     Chr.    Heinzerling.     Berlin,   1888.     (T. 
Fischer. ) 

Traite"  de  Chiinie  applique'e  a  Plndustrie.    Adolphe  Renard.     Paris,  1890. 

A  Dictionary  of  Applied  Chemistry.    T.  E.  Thorpe.    3  Vols.     London,  1891- 
1893.     (Longmans,  Green  and  Co.) 

Lehrbuch  der  technischen  Chemie.      Dr.  H.  Ost.    3d  Ed.     Berlin,  1898.     (R. 
Oppenheiiner.) 

Handbook  of  Industrial  Organic  Chemistry.      S.  P.  Sadtler.     Philadelphia.     2d 
Ed.     1895.     (J.  B.  Lippincott.) 

Handbuch  der  chemischen  Technologie.     Dr.   O.  Dammer.     5  Vols.     Vol.  I, 

1895.  Vol.  II,  1895.     Vol.  Ill,  1896.     Stuttgart.     (F.  Enke.) 

Chemistry  for  Engineers  and  Manufacturers.     Bertram  Blount  and  A.  G.  Bloxam. 
2  Vols.     London,  1896.     (Griffin  and  Co.) 

Chemical  Technology.     R.  Wagner.     Translated  by  Wm.  Crookes.    New  York, 
1897.     (D.  Appleton  and  Co.) 

Encyclopaedisches  Handbuch  der  technischen  Chemie.    F.  Stohmann  und  Bruno 
Kerl.     Vol.  I,  1888.    Vol.  II,  1889.     Vol.  Ill,  1891.     Vol.  IV,  1893.    Vol.V, 

1896.  Braunschweig.     (F.  Vieweg.) 

Chemical  Technology.    Edited  by  C.  E.  Groves  and  William  Thorp. 
Vol.  I,  Fuel,  1889. 
Vol.  II,  Lighting,  1895. 
V^l.  Ill,  Gas  and  Electric  Lighting,  etc. 

xix 


ABBREVIATIONS   OF  THE   NAMES    OF    JOURNALS, 

FREQUENTLY   OCCURRING   IN   THE    LITERATURE    OF    INDUSTRIAL    CHEMISTRY. 

A.  or  Ann.  =  Annalen  der  Chemie  und  Pharmacie,  by  Liebig  and  others, 

1832-98+. 
Ann.  chim.  phys.  =  Annales  de  Chimie  et  de  Physique.     Paris,  7  series,  1789- 

1898 +. 

Ber.  =  Berichte  der  deutschen  chemischen  Gesellschaf t.     Berlin,  1868-98  + . 
Bull.  Soc.  Chim.  =  Bulletin  des  Seances  de  la  Socie'te'  chimique  de  Paris.     2 

series,  1804  +  . 

Chem.  Centralb.  =  Chemisches  Centralblatt.    4  series,  1829-98  -f . 
Chem.  Ind.  =  Zeitschrift  fur  die  chemische  Industrie.     1887  +. 
C.  N.  or  Chem.  N  =  Chemical  News.     1860-98  + . 
C.  R.  or  Compt.  rend.  =  Comptes-rendus  hebdomadaires  des  Seances  de  1'  Acade- 

mie  des  Sciences.     Paris,  1835-98  +  . 
Chem.  Zeit.  =  Chemiker-Zeitung.     1877-1898  +  . 
Dingl.  J.  =  Dingler's  polytechnisches  Journal.     1820-98  +. 
Eng.  Min.  Jour.  =  Engineering  and  Mining  Journal.     1866-98  +  . 
Jahresb.  =  Jahresbericht  tiber  die  Fortschritt  der  Chemie,  u.  s.  w. 
J.  Am.  Chem.  Soc.  =  Journal  of  the  American  Chemical  Society.    New  York, 

1879-98  +  . 

J.  Chem.  Soc.  =  Journal  of  the  Chemical  Society  of  London.     1849-98  + . 
J.  Soc.  Chem.  Ind.  ==  Journal  of  the  Society  of  Chemical  Industry.     London, 

1882-98  +  . 

W.  J.  =  Wagner's  Jahresbericht  der  chemischen  Technologic.     1855-98  +. 
Zeitschr.  angew.  Chem.  =  Zeitschrift  fur  angewandte  Chemie.     Berlin,   1887- 

98+. 

Zeitschr.  anorg.  Chem.  =  Zeitschrift  fur  anorganische  Chemie.     1892-98  +. 
Zeitschr.  Chem.  Ind.  =  Zeitschrift  fur  die  chemische  Industrie.     1887  + . 


OUTLINES  OF  INDUSTRIAL  CHEMISTRY 


PART   I 
INORGANIC  INDUSTRIES 


INTRODUCTION 

INDUSTRIAL  chemistry  deals  with  the  preparation  of  products 
from  raw  materials,  through  the  agency  of  chemical  change.  But 
there  is  an  occasional  exception  to  this  definition ;  for  a  few  indus- 
tries, depending  on  strictly  mechanical  changes,  are  classed  among  the 
chemical  industries.  Since  a  sharp  line  cannot  be  drawn  between 
chemical  and  mechanical  technology,  a  study  of  the  former  neces- 
sarily involves  some  consideration  of  the  mechanical  appliances  and 
apparatus,  by  means  of  which  the  chemical  reactions  are  carried  out. 

The  products  of  chemical  industry  are  exceedingly  numerous  and 
varied  in  character,  but  comparatively  few  come  into  the  hands  of 
the  mass  of  the  people  for  direct  consumption.  Many  of  them  are 
used  only  in  making  other  substances,  for  it  is  often  the  case  that 
the  finished  product,  by-product,  or  waste-  from  one  industry,  be- 
comes the  raw  material  for  another,  and  it  rarely  happens  that 
one  manufacturer,  starting  with  the  raw  materials  found  in  nature, 
produces  from  them  articles  for  popular  use.  Thus  the  chemical 
industries  become  a  network  of  interlacing  processes,  and  in  con- 
sidering one  it  is  often  difficult  to  separate  it  from  others  which 
have  a  more  or  less  direct  bearing  upon  it.  Furthermore,  as  com- 
petition has  become  very  close  in  many  lines,  the  use  which  may 
be  made  of  by-products  and  waste  is  so  important,  that  processes 
are  often  carried  out  with  the  view  of  obtaining  larger  yields  or 
better  quality  of  the  by-products,  which  may  have  become  a  source 
of  considerable  profit.  In  a  few  instances,  it  might  be  said  that 
B  1 


2  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

what  were  originally  the  by-products  are  now  the  chief  products 
and  main  support  of  these  particular  industries.  This  is  especially 
true  in  the  case  of  the  Leblanc  Soda  Industry,  which  would  long 
since  have  been  abandoned  were  it  not  for  its  production  of  hydro- 
chloric acid.  The  utilization  of  waste  materials  furnishes  an  almost 
inexhaustible  subject  for  investigation  by  the  industrial  chemist. 

The  manipulations  of  most  frequent  occurrence  in  the  various 
processes  are  here  defined  and  explained  for  the  sake  of  brevity  in 
the  text. 

LIXIVIATION 

Lixiviation  is  the  process  of  separating  soluble  from  insoluble 
substances  by  dissolving  the  former  in  water  or  some  other  solvent. 
The  mixture  of  substances  is  put  into  a  suitable  vessel,  the  solvent 
poured  over  it,  and  the  whole  allowed  to  stand  until  a  strong  solu- 
tion is  obtained,  which  is  then  drawn  off  from  the  residue.  This 
process  is  repeated  as  often  as  necessary,  until  the  desired  amount 
of  soluble  matter  has  been  removed.  Sometimes  the  mixture  is  put 
into  baskets,  or  on  gratings,  which  are  suspended  in  tanks  of  water. 
The  solution  being,  denser  than  the  solvent,  sinks  to  the  bottom  as  it 
forms,  and  water  comparatively  free  from  dissolved  material  is  thus 
constantly  brought  into  contact  with  the  substance  to  be  lixiviated. 
The  insoluble  substance  remains  on  the  grating  or  in  the  baskets. 
When  desired,  the  soluble  material  may  be  recovered  from  the  solu- 
tion by  evaporation  or  precipitation.  Extraction  is  the  term  usually 
employed  when  some  solvent  other  than  water  is  used  in  lixiviating. 
Thus  we  speak  of  extraction  by  steam,  alcohol,  carbon  disulphide, 
etc. 

LEVIGATION 

Levigation  is  the  process  of  grinding  an  insoluble  substance  to  a 
fine  powder,  while  wet.  The  material  is  introduced  into  the  mill 
together  with  water,  in  which  the  powdered  substance  remains  sus- 
pended, and  flows  from  the  mill  as  a  turbid  liquid  or  thin  paste, 
according  to  the  amount  of  water  employed.  There  is  no  loss  of 
material  as  dust,  nor  injury  or  annoyance  to  the  workmen.  Further, 
any  soluble  impurities  in  the  substance  are  dissolved,  and  the  prod- 
uct thereby  purified.  The  greatest  advantage  of  this  process  is  the 
facility  it  affords  for  the  subsequent  separation  of  the  product  into 
various  grades  of  fineness,  because  of  the  slower  subsidence  of  the  finer 
particles  from  suspension.  The  turbid  liquid,  flows  into  the  first  of 


INTRODUCTION  8 

a  series  of  tanks,  and  is  allowed  to  stand  for  a  certain  time.  The 
coarsest  and  heaviest  particles  quickly  subside,  leaving  the  finer 
material  suspended  in  the  water,  which  is  drawn  from  above  the 
sediment  into  the  next  tank.  The  liquid  is  passed  from  tank  to 
tank,  remaining  in  each  longer  than  it  remained  in  the  preceding, 
since  the  finer  and  lighter  the  particles,  the  more  time  is  necessary 
for  their  deposition.  In  some  cases  a  dozen  or  more  tanks  may  be 
used,  and  the  process  then  becomes  exceedingly  slow,  as  very  fine 
slimes  or  muds  may  require  several  weeks  for  the  final  settling. 
But  as  a  rule,  from  three  to  five  days  is  sufficient. 

The  term  "  levigation  "  is  now  often  applied  to  mere  sedimenta- 
tion, a  substance  being  simply  stirred  up  in  water,  without  previous 
wet-grinding,  in  order  to  separate  the  finer  from  the  coarser  parti- 
cles, as  above. 

EVAPORATION 

Evaporation,  in  a  technical  sense,  denotes  the  conversion  of  a 
liquid  into  a  vapor  for  the  purpose  of  separating  it  from  another 
liquid  of  higher  boiling  point,  or  from  a  solid  which  is  dissolved  in 
it.  In  the  great  majority  of  cases,  the  liquid  evaporated  is  water. 
If  the  liquid  evaporated  is  to  be  recovered,  the  vapors  are  con- 
densed, and  the  process  then  becomes  one  of  Distillation  (see  p.  7). 

There  are  four  general  methods  of  evaporation :  — 

1.  Spontaneous  evaporation  in  the  open  air. 

2.  Evaporation  by  application  of  heat  directly  from  a  fire  to 
the  vessel  containing  the  liquid. 

3.  Evaporation  by  indirect  application  of  heat  from  the  fire,  as 
by  means  of  steam,  with  or  without  pressure. 

4.  Evaporation  under  reduced  pressure. 

The  first  method,  by  spontaneous  evaporation  in  the  open  air,  is 
comparatively  slow,  and  requires  exposure  of  very  large  surfaces  of 
liquid.  The  time  necessary  depends  upon  the  temperature  and 
humidity  of  the  air,  and  the  completeness  with  which  the  vapors 
are  removed  from  the  surface  of  the  liquid;  hot,  dry  weather,  es- 
pecially if  a  brisk  wind  is  blowing,  evaporates  water  quite  rapidly. 
This  process  is  only  used  for  the  manufacture  of  salt  from  sea 
water,  or  from  natural  brines.  In  certain  warm  countries  con- 
siderable quantities  of  salt  are  thus  prepared,  and  in  this  country 
some  is  made  from  a  brine  found  near  Syracuse,  N.Y.  Sometimes 
weak  brines  are  allowed  to  trickle  in  fine  streams  over  tall  piles 
or  " ricks"  of  brushwood  in  the  open  air.  The  liquid  being  so 
exposed  in  thin  layers,  to  the  air  and  wind,  is  concentrated  to  such 


4  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

a  degree  that  it  will  pay  to  complete  the  evaporation  by  artificial 

heat. 

The  second  method,*  by  direct  application  of  heat  from  a  fire,  is 

very  largely  used  in  the  arts.     This  may  be  done  in  two  general 

ways :  — 

(a)  The  flames,  or  hot  gases  from  the  fire,  are  generally  allowed 

to  play  directly  on  the  bottom  of  the  vessel  containing  the  liquid ; 

or  they  may  pass  through 
flues  or  pipes,  set  into 
the  vessel,  so  that  the 
liquid  surrounds  them  on 
all  sides  (Fig.  1).  Such 


FIG.  1. 


pans  are  often  several 
yards  in  length,  and  may 
contain  one  large  flue,  or 

several  small  ones,  according  to  the  work  desired ;  but  this  form  of 
apparatus  is  expensive  to  build,  and  difficult  to  keep  in  repair. 

(b)  The  flames  and  hot  gases  may  be  conducted  over  the  surface 
of  the  liquid  to  be  evaporated.  This  mode  is  only  used  for  coarse 
and  common  products,  or  in  the  concentration  or  recovery  of  waste 
materials.  But  it  has  the  advantage,  that  the  bottom  of  the  pan  is 
less  liable  to  be  injured  by  the  crusting  of  a  precipitate  upon  it. 
Another  point  often  in  favor  of  surface  heating,  is  that  the  liquid  is 
evaporated  in  a  reducing  atmosphere.  But  as  flue  dust  and  ashes 
are  liable  to  fall  into  the  pans,  the  product  is  usually  impure.  Large 
shallow  pans  are  used,  which  are  generally  arched  over  with  brick, 
in  order  that  the  heat  may  be  better  utilized,  through  radiation  from , 
the  brick  walls.  There  are 
various  ways  of  setting  the 
pans  for  this  process ;  a  sim- 
ple method  is  shown  in 
Fig.  2.  A  modification  of 
this  method  is  the  use  of  a 
long  cylinder,  set  at  a  slight 
incline,  an^  revolving  about  its  longitudinal  axis  (Fig.  3).  The 
lower  end  is  open  for  the  entrance  of  the  flames  and  gases  from  the 
grate  (A),  which  pass  through  the  cylinder  (B),  on  their  way  to  the 
chimney  (D).  The  hot  gases  are  often  passed  through  the  flues  of  a 
boiler  (C),  to  utilize  the  waste  heat.  The  solution  to  be  evaporated 


FIG.  2. 


*  To  save  expense,  the  waste  heat  from  calcination  or  furnacing  operations  is 
frequently  utilized. 


INTRODUCTION  5 

is  fed  into  the  cylinder  at  the  upper  end  in  a  small  stream,  and 
comes  in  direct  contact  with  the  flame.  The  water  is  evaporated, 
and  the  solid  matter  is  delivered  into  the  pit  or  wagon  (E)  at  the 
lower  end  of  the  furnace,  in  a  dry  and  calcined  state.  Such  fur- 
naces are  frequently  used  for  evaporating  waste  liquors  to  recover 


FIG.  3. 


the  salts  which  they  contain ;   and  for  the  treatment  of  sewage  and 
other  liquid  refuse. 

The  third  method  of  evaporation,  by  the  use  of  steam  heat,  is 
very  often  employed  where  there 'is  danger  of  injury  to  the  product 
by  overheating. 

(a)  Jacketed  pans  or  kettles  may  be  used.     These  are  simply 
double-walled  vessels,  the  steam  being  admitted  between  the  walls. 

(b)  The  steam  may  be  allowed  to  circulate  through  coils  of  pipe, 
placed  inside  the  vessel,  which  is  sometimes  made  of  wood.     The 
temperature  of  the  liquid  depends  on  the  steam  pressure ;  very  often 
exhaust  steam  is  employed. 

The  fourth  method,  evaporation  in  vacuo,  is  merely  a  modifica- 
tion of  either  the  second  or  third  method,  but  is  considered  sepa- 
rately for  convenience.  The  boiling  point  of  a  liquid  may  be  very 
materially  lowered  by  reducing  the  pressure  within  the  vessel. 
Hence,  solutions  containing  substances  which  would  be  injured  by 
the  heat  necessary  to  boil  them  under  the  atmospheric  pressure, 
or  liquids  boiling  at  very  high  temperatures,  are  evaporated  in 
vacuum  pans. 

The  different  forms  of  apparatus  used  for  vacuum  evaporation 
vary  much  in  their  details,  but  all  depend  on  the  principle  of 
reduced  pressure.  The  essential  parts  of  the  plant  are  the  vacuum 
pan  or  still,  the  pump  for  exhausting  the  air  and  steam  from  the 
pan  and  sending  them  to  the  condenser,  and  the  heating  apparatus. 
The  vacuum  pan  is  usually  a  globular  copper  or  iron  vessel,  pro- 
vided with  a  manhole,  a  pressure  gauge,  and  a  discharging  valve. 
Very  often  a  piece  of  heavy  plate  glass  is  set  in  the  side  to  afford  a 


6  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

view  of  the  interior  during  evaporation.  On  the  top  of  the  pan  is 
a  dome  or  short  tower,  from  which  a  pipe  leads  to  a  receptacle, 
called  the  "  catch-all/7  that  retains  any  liquid  which  may  escape  from 
the  pan.  A  small  pipe  returns  this  liquid  to  the  pan,  and  a  larger 
one  connects  the  "  catch-all "  with  the  vacuum  pump,  which  is  an 
ordinary  double-cylinder  air  pump  of  large  size,  driven  by  an  engine. 
An  injector  pump,  which  condenses  the  steam  directly,  may  be  used. 
The  pan  is  generally  heated  by  steam  coils  within  it,  or  by  a  steam 
jacket,  or  by  both. 

A  very  efficient  method  of  vacuum  evaporation  is  that  obtained 
by  the  use  of  Multiple  Effect  Systems.  In  these  greater  economy  of 
fuel  for  heating  is  secured.  The  apparatus  consists  usually  of  three 
or  four  simple  vacuum  pans,  so  joined  together  that  the  steam  from 
the  boiling  liquid  in  the  first  pan  is  made  to  pass  through  the  coils 
and  jacket  of  the  second  pan,  and  the  steam  generated  in  the  second 
pan  goes  through  the  coils  and  jacket  of  the  third,  and  so  on 
through  the  system.  The  vacuum  maintained  in  each  pan  of  the 
series  is  greater  than  in  the  one  preceding.  Hence,  notwithstand- 
ing its  increased  concentration,  the  boiling  point  of  the  liquid  in  the 
second  pan  is  so  low,  that  the  steam  from  the  first  pan  is  sufficiently 
hot  to  boil  it.  Similarly  the  steam  from  the  second  pan  is  made  to 
boil  the  liquid  in  the  third,  in  which  there  is  still  less  pressure,  and 
so  on  to  the  fourth  pan,  in  which  the  highest  vacuum  is  maintained. 
As  a  rule  only  four  pans  are  used,  for  it  is  very  difficult  to  sustain 
the  vacuum  sufficiently  to  work  another  pan  in  the  series.  In  many 
plants  only  three  pans  (triple  effects)  are  used. 

An  effective  modification  of  this  method  is  the  apparatus  known 
as  the  Yaryan  Evaporator  (Fig.  4).  It  is  made  in  triple  and  quad- 
ruple effects,  and  each  pan  is  exactly  like  its  neighbors.  It  consists 
of  an  outside  shell  of  iron,  within  which  is  a  system  of  small  tubes 
(A,  A),  joined  together  in  groups  of  five  or  six,  each  group  constitut- 
ing a  section  or  unit.  The  tubes  in  each  unit  are  so  connected  at 
the  ends  as  to  form  one  continuous  coil.  The  liquor  to  be  evaporated 
is  run  through  the  several  coils  thus  constructed  in  each  pan.  The 
tubes  in  the  first  pan  are  heated  by  steam,  introduced  into  the  shell 
directly  from  a  boiler.  As  the  liquid  flows  through  the  tubes,  it  is 
brought  to  boiling,  and  the  steam  generated  mingles  with  it,  convert- 
ing the  whole  mass  into  foam,  which  runs  through  the  coil  and 
spurts  against  a  baffle  plate  in  the  "separator"  (B,  B),  which  is  an 
enlarged  chamber  at  the  end  of  the  shell.  The  steam  and  liquid  are 
separated,  the  liquid  falling  to  the  bottom  and  running  off  into  the 
receiver  (C),  to  be  passed  through  the  tubes  of  the  next  pan.  The 


INTRODUCTION  7 

steam  rises,  passing  through  the  steam  dome  and  "catch-all"  (D), 
and  then  into  the  shell  of  the  next  "  effect,"  through  the  coils  of 
which  the  liquid  is  passing  under  still  greater  vacuum,  and  so  on 
through  the  system.  The  apparatus  is  very  economical  in  its  use  of 
fuel,  and  as  the  liquid  is  exposed  in  thin  layers  to  the  action  of  the 
heat,  the  evaporation  is  very  rapid;  hence  the  liquid  is  subjected  to 
a  high  temperature  for  only  a  short  time.  The  apparatus  is  nearly 


automatic  in  its  action,  and  needs  but  little  attention.  It  can  be 
stopped  and  started  very  quickly,  since  it  contains  only  a  small 
quantity  of  liquid  at  one  time,  and  it  occupies  but  little  floor  space 
when  the  several  "  effects  "  are  placed  one  over  the  other. 

The  ordinary  form  of  vacuum  pan  evaporates  about  8 \  Ibs.  of  water 
per  pound  of  coal,  but  it  is  said  that  the  best  forms  of  Yaryan  appa- 
ratus evaporate  from  23|-  to  25  Ibs.  of  water  per  pound  of  coal  in  a 
triple  effect,  and  30J-  Ibs.  in  a  quadruple  effect.* 

DISTILLATION 

Distillation  is  the  process  of  vaporizing  a  liquid  and  recovering  it 
by  condensing  the  vapors.  The  liquid  formed  by  this  condensation 
is  called  the  distillate.  Distillation  is  chiefly  employed  to  separate 
a  liquid  from  non-volatile  matter  dissolved  or  suspended  in  it ;  or  to 
separate  one  liquid  from  a  mixture  of  liquids  of  different  boiling 
points ;  that  one  having  the  lowest  boiling  point  being  the  first  to 
begin  to  pass  off  as  vapor. 

But  the  separation  of  two  liquids  which  are  miscible  with  each 

*  J.  Soc.  Chem.  Ind.,  1895, 112. 


8 


OUTLINES  OF  INDUSTRIAL  CHEMISTRY 


other  is  never  complete  by  this  means,  and  is  less  perfect  the  nearer 
their  boiling  points  are  together.  Liquids  which  are  miscible  in  all 
proportions,  may  be  separated  quite  completely,  provided  there  are 
a  few  degrees  difference  in  their  boiling  points,  by  employing  the 
principle  of  fractional  condensation  of  the  vapors.  This  consists  in 
passing  the  mixed  vapors  through  a  condenser  which  is  kept  at  a 
constant  temperature  between  the  boiling  points  of  the  liquids.  Thus 
the  vapors  of  the  high-boiling  liquid  being  cooled  below  the  boiling 
point  of  that  liquid  are  condensed,  while  the  vapors  of  the  low-boiling 
liquid  being  still  hotter  than  its  boiling  point,  cannot  condense,  but 
pass  on  to  another  part  of  the  apparatus,  where  they  are  condensed 
separately.  When  the  high-boiling  distillate  condenses,  it  carries 
with  it  more  or  less  of  the  low-boiling  liquid,  and  hence  should  usu- 
ally be  returned  to  the  boiler  and  redistilled.  In  such  mixtures  as 
this,  there  is  a  gradual  rise  in  the  boiling  point  during  the  entire 
distillation. 

The  chief  parts  of  every  distilling  apparatus  are  the  boiler  or  still 
and  the  condenser.  In  practical  work  the  appliance  for  fractional 
condensation  is  placed  between  the  still  and  the  condenser.  It  may 
be  an  apparatus,  called  a  "  dephlegmator,"  in  which  the  vapors  are 
forced  to  bubble  through  a  layer  or  column  of  the  condensed  higher- 
boiling  liquid ;  or  the  mixed  vapors  may  pass  through  a  tower  or 

pipe,  kept  at  a  constant 
temperature,  just  above  the 
boiling  point  of  the  low- 
boiling  liquid.  The  still 
is  usually  iron,  copper,  or 
other  metal,  heated  directly 
by  a  furnace,  a  steam  jacket, 
or  a  coil. 

In  Coupler's  still  (Fig.  5) 
a  tower  (A)  is  placed  on  top 
of  the  boiler  (B);  between 
the  tower  and  the  con- 
denser is  a  series  of  bulbs 

(C,  C)  surrounded  by  a  water  bath,  which  may  be  kept  at  any  de- 
sired temperature.  While  the  mixed  vapors  are  passing  through 
the  bulbs,  the  high-boiling  constituents  are  condensed,  and  only  the 
vapor  of  the  more  volatile  liquid  passes  through  (E)  to  the  con- 
denser (F).  From  each  bulb  a  pipe  (D)  leads  back  to  the  tower, 
into  which  the  condensed  heavy  liquid  is  delivered,  to  be  redis- 
tilled or  dephlegmated. 


INTRODUCTION 


The  French  column  (Fig.  6)  is  very  similar  to  the  Coupler's  appa- 
ratus, but  instead  of  bulbs,  a  series  of  U-tubes  (C)  surrounded  by  a 
water  bath  is  used.  The  column 
or  dephlegmator  (B)  is  divided  into 
chambers  by  plates,  each  of  which 
has  a  central  opening  covered  by 
a  dome;  a  small  overflow  pipe 
passes  from  each  plate  to  the  next. 
The  vapors  from  the  boiler  (A)  pass 
up  through  the  central  openings 
and  bubble  out  under  the  edges 
of  the  domes  through  the  layer 
of  liquid  on  each  plate.  The  liquid 
thus  condensed  flows  down  through 
the  overflow  pipes,  and  returns  to 
the  boiler. 

The  Coffey  still  (Fig.  7)  is  much 
used  for  alcohol  and  gas  liquor  dis- 
tillation. This  consists  of  two 
towers,  one,  called  the  "analyzer" 

(E),  receiving  free  steam  from  the  boiler,  and  the  other,  called  the 
"  rectifier  "  (G),  containing  a  long  coil  of  pipe  (C,  C),  through  which 


FIG.  6. 


FIG.  7. 


the  liquid  to  be  distilled  flows  on  its  way  to  the  analyzer.      The 
analyzer  is  divided  into  a  series  of   chambers  by  horizontal,  per- 


10  OUTLINES  OF  INDUSTRIAL   CHEMISTRY 

f orated  plates  (A) ;  from  each  plate  an  overflow  pipe  (F)  passes 
down  and  dips  into  a  shallow  cup  (H)  on  the  next  plate  below 
and  holding  liquid  enough  to  form  a  hydraulic  seal  at  the  lower 
end  of  each  overflow  pipe.  These  pipes  project  about  an  inch,  or  an 
inch  and  a  half  above  the  plate  in  which  they  are  set,  thus  determin- 
ing the  depth  of  the  liquid  layer  on  each  plate.  The  rectifier  is  also 
divided  into  chambers  by  perforated  plates,  but  it  has  overflow  pipes 
in  its  lower  half  only.  In  the  chambers  lie  the  coils  of  pipe  (C) 
through  which  the  liquid  to  be  distilled  passes  on  its  way  to  the 
analyzer.  This  still  works  as  follows:  Steam  from  the  boiler  is 
blown  through  (K)  into  the  analyzer,  and  passes  from  the  top  of  the 
analyzer  through  the  pipe  (L)  to  the  rectifier.  The  liquid  to  be  dis- 
tilled is  pumped  through  the  pipe  (B)  and  the  coil  (C)  in  the  recti- 
fier, and  is  delivered  at  the  top  of  the  analyzer  through  the  pipe  (D). 
The  cold  liquid  is  heated  by  the  steam  surrounding  the  coils,  and  is 
delivered  hot  at  the  top  of  the  analyzer. 

Since  steam  is  being  forced  up  through  the  perforations,  the  liquid 
cannot  pass  down  through  them,  but  is  forced  to  spread  out  over 
the  plate,  and  run  down  the  overflow  pipe  (F)  to  the  next  plate, 
and  so  through  the  analyzer.  The  steam,  bubbling  up  through  the 
thin  layers  of  liquid,  heats  it  very  hot,  and  causes  the  volatile  sub- 
stances to  distill  off  with  the  steam.  This  mixture  of  steam  and  vola- 
tile matter  passes  from  the  top  of  the  analyzer,  through  (L),  to  the 
bottom  of  the  rectifier.  During  its  passage  up  the  rectifier,  the  steam 
is  condensed  by  coming  into  contact  with  the  cold  pipes  (C,  C), 
through  which  the  liquid  is  flowing  to  the  analyzer.  Thus  only  the 
more  volatile  matters  pass  out  at  the  top  of  the  rectifier,  and  go  to 
the  condenser  (0).  The  water  condensed  in  the  rectifier  contains 
some  volatile  matter,  so  it  is  pumped  to  the  top  of  the  analyzer  and 
mixes  with  the  fresh  liquor  to  be  distilled.  From  the  bottom  of  the 
analyzer  a  waste  pipe  (J)  carries  off  the  spent  liquor  which  has 
been  deprived  of  its  volatile  matter. 

Distillation  in  vacuum  is  sometimes  employed,  and  will  be  de- 
scribed in  connection  with  the  industries  in  which  it  is  used. 


SUBLIMATION 

Sublimation  is  the  process  of  vaporizing  a  solid  substance  and 
condensing  the  vapors  to  again  form  the  solid  directly,  without 
passing  through  an  intermediate  liquid  state.  There  are  very  few 
substances  which  vaporize  without  melting,  but  in  all  cases  of  sub- 
limation, the  change  from  the  vapor  to  the  solid  state,  is  direct,  and 


INTRODUCTION  11 

without  any  formation  of  liquid.  The  sublimed  body  is  recovered 
unchanged  chemically,  but  its  physical  properties  are  often  more 
or  less  altered. 

Sublimation  is  influenced  by  the  pressure  within  the  vessel,  and 
is  generally  carried  on  under  atmospheric  pressure  only.  The 
process  is  employed  as  a  means  of  purification  of  certain  substances, 
which  are  heated  in  closed  pans  or  retorts. .  In  most  cases,  the 
temperature  does  not  exceed  a  low  red  heat.  Dissociation  often 
occurs  in  the  process. 

FILTRATION 

Filtration  is  the  process  of  separating  suspended  solid  matter 
from  a  liquid,  by  causing  the  latter  to  pass  through  the  pores  of 
some  substance,  called  a  filter.  The  liquid  which  has  passed 
through  the  filter  is  called  the  filtrate.  The  filter  may  be  paper, 
cloth,  cotton-wool,  asbestos,  slag-  or  glass-wool,  unglazed  earthen- 
ware, sand,  or  other  porous  material. 

Filtration  is  very  frequently  employed  in  chemical  technology, 
and  it  often  presents  great  difficulties.  In  most  technical  opera- 
tions, cotton  cloth  is  the  filtering  material,  but  occasionally  woollen 
or  hair  cloth  is  necessary.  The  cloth  may  be  fastened  on  a  wooden 
frame  in  such  a  way  that  a  shallow  bag  is  formed,  into  which  the 
turbid  liquid  is  poured.  The  filtrate,  in  this  case,  is  cloudy  at  first, 
but  soon  becomes  clear,  and  then  the  turbid  portion  is  returned  to 
the  filter.  Filtration  is  often  retarded  by  the  presence  of  fine, 
slimy  precipitates,  or  by  the  formation  of  crystals  in  the  interstices 
of  the  cloth,  from  the  hot  solution.  Any  attempt  to  hasten  filtra- 
tion, by  scraping  or  stirring  the  precipitate  on  the  cloth,  will  always 
cause  the  filtrate  to  run  turbid. 

A  better  form  is  the  "  bag-filter,"  which  is  a  long,  narrow  bag 
of  twilled  cotton,  supported  by  an  outside  cover  of  coarse,  strong 
netting,  capable  of  sustaining  a  considerable  weight  and  hydrostatic 
pressure.  These  bags  are  often  five  or  six  feet  long,  and  eight 
inches  or  more  in  diameter.  The  open  end  of  the  bag  is  tied  tightly 
around  a  metallic  ring  or  a  nipple,  by  which  the  whole  is  suspended, 
and  through  which  the  liquor  to  be  filtered  is  introduced.  When 
hot  liquids  are  filtered,  the  bags  are  often  hung  in  steam-heated 
rooms,  the  temperature  being  nearly  that  of  the  liquid. 

In  pressure  filtration,  the  liquid  is  forced  through  the  interstices 
of  the  filter  by  direct  atmospheric  pressure,  the  air  being  exhausted 
from  the  receiver;  or  by  hydrostatic  pressure,  obtained  either  by 
means  of  a  high  column  of  the  liquid,  or  by  a  force  pump.  By  the 


12  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

first  method,  called  suction  filtration,  the.  liquid  may  be  forced 
downward  through  the  filter  into  a  receiver ;  the  precipitate  collects 
on  the  top  of  the  filter  and  becomes  a  part  of  the  filtering-  layer. 
This  sometimes  causes  difficulty,  for  the  particles  of  certain  precipi- 
tates unite  to  form  an  impervious  layer.  Or  the  filtrate  may  be 
drawn  upward  through  the  filter,  which  is  suspended  in  the  liquid 
to  be  filtered;  thus  clogging  does  not  occur  so  easily,  as  a  large 
part  of  the  precipitate  settles  to  the  bottom  of  the  vessel  and  does 
not  come  in  contact  with  the  filter  until  most  of  the  liquid  has  been 
drawn  off. 

In  technical  work,  pressure  is  usually  obtained  by  the  filter  press 
(Figs.  8  and  8  a).    This  is  a  strong  iron  frame,  in  which  a  number  of 


cast-iron  or  bronze  filter  cells  are  supported.  Each  cell  is  made  up  of 
two  flat  metal  plates  with  raised  edges,  separated  by  a  hollow  "  dis- 
tance frame  "  of  the  same  metal.  There  is  a  hole  in  the  centre  of 
each  plate,  and  grooves  on  each  surface  leading  to  an  opening  at  the 
lower  edge  of  the  plate.  A  filter  is  made  of  two  pieces  of  cloth, 
slightly  larger  than  the  plates,  sewed  together  along  the  margin  of 
a  small  circular  opening  cut  in  the  centre  of  each.  One  piece 
of  the  cloth  is  passed  through  the  hole  in  the  plate,  and  then  both 
pieces  are  spread  out  smoothly,  one  on  either  side  of  the  plate. 
Another  plate  is  prepared  in  the  same  way,  and  a  distance  frame 
having  been  placed  between  them,  the  cell  thus  formed  is  set  verti- 
cally in  the  press  frame,  where  it  is  supported  by  lugs  on  each 
plate  and  distance  frame.  When  the  desired  number  of  cells  are 
ready,  they  are  tightly  clamped  together  by  means  of  a  heavy 
screw,  which  passes  through  one  end  of  the  press  frame.  Thus  a 


INTRODUCTION 


13 


series  of  cells,  lined  with  filter  cloth  and  connected  by  a  straight 
channel  through  the  central  holes,  is  formed.  A  powerful  force 
pump  drives  the  liquid  to  be  filtered  into  the  cells,  where  it  passes 
from  one  to  the  other  until  they  are  all  filled.  The  hydrostatic 
pressure  forces  the  liquid  through  the  filters  into  the  grooves  in  the 
plates,  along  which  it  flows,  and  escapes  through  the  openings  at 
the  lower  side  of  the  plate.  The  sediment  retained  by  the  cloth 
collects  in  the  cell  and  forms  a  solid  cake,  which  finally  fills  each 


FIG.  8 a. 

cell  completely.  The  process  is  then  stopped,  the  cells  taken  apart, 
and  the  cake  of  sediment  having  been  removed,  the  cells  are 
returned  to  the  press  frame,  to  be  again  put  into  operation.  The 
filtrate  is  caught  in  a  trough. 

In  another  form  of  press,  instead  of  the  central  opening,  there 
is  a  hole  in  the  corner  of  each  plate  and  distance  frame  in  such  a 
position  that,  when  placed  in  the  press,  the  holes  form  a  continuous 
channel  through  the  corner  of  the  whole  series  of  cells.  A  small 
hole  drilled  on  the  inside  of  each  distance  frame,  at  right  angles 
to  the  direction  of  the  channel,  admits  the  liquid  into  each  cell. 
The  filter  is  a  piece  of  cloth  hung  over  the  distance  frame  in  such 
a  way  that  both  sides  of  the  frame  are  covered.  A  frame  so 
covered  is  put  between  each  pair  of  grooved  plates.  Small  holes 


14 


OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


are  cut  in  the  cloth  to  correspond  to  the  channel  in  the  corners 
of  the  cells.  The  method  of  nitration  is  the  same  as  in  the  central 
feed  machines. 

The  pressure  obtained  by  the  force  pump  may  be  only  a  few 
pounds,  or  it  may  rise  to  several  hundred  pounds  per  square  inch. 
The  filter  press  may  contain  from  a  dozen  to  fifty  or  more  cells,  and 

these  cells  may  be  as  large  as 
four  feet  in  diameter.  For 
many  purposes  the  press  is  sur- 
rounded by  coils  or  jackets, 
through  which  steam  or  refrig- 
erating solutions  may  be  circu- 
lated, according  as  hot  or  cold 
filtration  is  desired. 

The  filter  press  is  very  rapid 
in  its  action  and  is  extensively 
employed  in  industrial  chemi- 
c:il  work.  For  use  with  acid 
or  corrosive  liquids,  the  plates 
and  distance  frames  are  often 
covered  with  lead  or  some  alloy 
which  is  not  easily  corroded. 

The  centrifugal  machine 
(Fig.  9)  is,  to  a  great  extent, 
replacing  the  filter  press  and 
other  filters,  especially  when 
crystals  are  to  be  removed. 

This  furnishes  the  most  rapid  method  and  leaves  the  substance 
almost  dry.  The  centrifugal  machine  is  a  cylindrical  box  or  basket 
(A)  of  wire  gauze  or  perforated  sheet  metal,  fixed  on  a  vertical 
shaft  (B),  which  rotates  at  a  very  high  speed.  The  contents  of  the 
box  are  driven  to  the  outer  wall  by  the  centrifugal  force,  the  solid 
matter  being  retained  by  the  gauze  or  screen.  The  liquid  passes 
through  and  is  caught  in  a  fixed  shell  (C),  surrounding  the 
rotating  basket.  These  machines  are  of  various  sizes  from  12  to  60 
inches  diameter,  and  8  to  36  inches,  depth  of  basket.  Two  general 
forms  are  in  use :  the  over-driven  type,  in  which  the  driving  pulley 
(P)  is  fixed  at  the  upper  end  of  the  shaft,  above  the  basket ;  and 
the  under-driven  type,  in  which  the  basket  is  placed  on  the  upper 
end  of  the  shaft,  and  the  pulley  below.  In  the  over-driven  type  it 
is  frequently  customary  to  suspend  the  shaft  in  flexible  bearings. 
Thus  the  basket  is  enabled  to  adjust  itself  to  any  change  in  the 


FIG.  9. 


INTRODUCTION  15 

centre   of   gravity,  caused   by  unequal   loading,  and   runs  without 
vibration. 

Sand  filters  are  sometimes  used  for  work  on  a  large  scale.  These 
are  made  as  follows :  Into  a  box  having  a  perforated  bottom,  is  put 
a  layer  of  coarse  gravel ;  this  is  covered  with  finer  pebbles ;  these 
by  sand,  and  a  jute  or  canvas  cloth  covers  the  whole.  A  wooden 
or  iron  grating  is  added  to  protect  the  filter,  when  the  sediment  is 
shovelled  out.  The  filter  is  often  placed  over  a  receptacle  from 
which  the  air  may  be  exhausted,  thus  affording  pressure  filtration 
if  necessary. 

CRYSTALLIZATION 

Crystals  are  chemically  homogeneous  bodies,  usually  having 
regular  polyhedral  forms,  and  whose  molecules  have  arranged  them- 
selves regularly  according  to  definite  laws.  The  tendency  to  form 
crystals  is  common  to  almost  all  chemical  compounds  under  certain 
conditions,  the  forms  of  the  crystals  being  characteristic  of  the 
substance. 

Crystals  may  form  from  a  fusion,  or  by  sublimation;  but  crys- 
tallization almost  always  takes  place  from  solution. 

In  the  majority  of  cases,  the  solubility  of  a  substance  increases 
as  the  temperature  of  the  liquid  rises,  until  a  point  is  reached  at 
which  no  more  of  the  substance  will  dissolve,  even  though  the 
solution  is  boiling.  When  a  liquid  has  dissolved  all  of  a  solid  that 
it  can  hold  in  solution  at  a  certain  temperature  and  pressure,  it  is 
said  to  be  saturated  for  that  temperature.  Any  decrease  in  the 
temperature  results  in  the  separation  of  a  part  of  the  substance, 
usually  as  crystals.  There  are  a  few  instances  where  the  maximum 
solubility  is  reached  at  temperatures  much  below  the  boiling  point 
of  the  solution,  the  most  notable  of  these  salts  being  sodium  car- 
bonate and  sodium  sulphate,  both  reaching  the  maximum  solubility 
below  35°  C.  During  the  formation  of  the  crystal,  there  is  a  ten- 
dency to  exclude  from  it  all  matter  not  homogeneous  with  it;  hence 
this  is  an  excellent  method  of  purifying  salts.  But  if  a  concentrated 
solution,  which  is  very  impure,  is  allowed  to  crystallize,  the  impuri- 
ties may  become  enclosed  in  or  entangled  among  the  crystals  as 
they  form,  producing  an  impure  product.  This  can  often  be  pre- 
vented by  stirring  the  solution  while  crystallizing,  thus  causing  the 
formation  of  very  fine  crystals  or  "crystal  meal,"  which  may  be 
more  readily  washed  free  from  mother-liquor  and  impurities.  The 
liquid  from  which  the  crystals  have  deposited,  is  called  the  mother- 
liquor  ;  it  contains  the  greater  part  of  the  soluble  impurities  present 


16  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

in  the  original  solution,  and  also  a  considerable  quantity  of  the  salt, 
which  has  not  deposited  as  crystals.  The  amount  of  the  latter 
depends  upon  the  temperature  at  which  the  crystallization  took 
place.  By  further  evaporation  more  crystals  may  be  obtained,  but 
they  are  less  pure  than  those  first  separated.  Thus  the  impurities 
accumulate  in  the  mother-liquor,  and  in  many  cases,  being  valuable 
salts  themselves,  are  recovered,  and  add  to  the  profits  of  the  indus- 
try. On  the  other  hand,  the  mother-liquors  from  some  processes 
are  the  cause  of  much  annoyance  and  expense  to  the  manufacturer, 
since  from  their  corrosive,  poisonous,  or  offensive  nature,  they  can- 
not be  run  into  the  streams  or  sewers,  and  their  disposal  in  some 
other  way  becomes  necessary. 

If  a  concentrated  solution  is  allowed  to  stand  quietly  while 
crystallizing,  especially  if  there  is  a  considerable  quantity  of  the 
liquid  and  the  temperature  falls  very  slowly,  the  crystals  formed 
are  usually  large  and  well  defined;  on  the  other  hand,  if  it  be 
stirred,  the  crystals  are  small  and  imperfectly  developed,  constitut- 
ing the  crystal  meal  above  mentioned.  Since  large  crystals  are  very 
compact  and  offer  a  relatively  small  surface  to  the  action  of  water, 
they  dissolve  very  slowly,  unless  pulverized.  Crystal  meal  dissolves 
more  readily,  and  for  this  reason  is  becoming  more  and  more  popular 
with  manufacturers. 

CALCINATION 

Calcination  is  the  process  of  subjecting  a  substance  to  the  action 
of  heat,  but  without  fusion,  for  the  purpose  of  causing  some  change 
in  its  physical  or  chemical  constitution.  The  objects  of  calcination 
are  usually:  (1)  to  drive  off  water,  present  as  absorbed  moisture, 
as  "  water  of  crystallization,"  or  as  "  water  of  constitution  " ;  (2)  to 
drive  off  carbon  dioxide,  sulphur  dioxide,  or  other  volatile  constit- 
uent ;  (3)  to  oxidize  a  part  or  the  whole  of  the  substance.  There 
are  a  few  other  purposes  for  which  calcination  is  employed  in 
special  cases,  and  these  will  be  mentioned  in  their  proper  places. 
The  process  is  often  called  "  roasting,'7  "  firing,"  or  "  burning,"  by 
the  workmen.  It  is  carried  on  in  furnaces,  retorts,  or  kilns,  and 
very  often  the  material  is  raked  over  or  stirred,  during  the  process, 
to  secure  uniformity  in  the  product. 

The  furnaces  used  for  calcining  substances  vary  much  in  their 
construction,  but  there  are  three  general  classes:  muffle,  reverber- 
atory,  and  shaft  furnaces  or  kilns. 

Muffle  furnaces  (Fig.  10)  are  so  constructed  that  neither  the  fuel 
nor  the  fire  gases  come  in  direct  contact  with  the  material  to  be 


INTRODUCTION 


17 


calcined.  A  retort  (A)  of  iron,  brickwork,  or  fire-clay,  is  placed 
over  the  fire  grate  (G).  Flues  (F,  F)  are  built  around  the  retort, 
and  through  these  the  hot  gases  from  the  fire  pass  on  their  way  to 
the  chimney  (E). 


*      G 

•        i 

F 

U                                A 

ItF 

</ 

FIG.  10. 

Reverberatory  furnaces  are  built  in  many  forms,  but  in  all  cases 
the  flames  and  hot  gases  from  the  fire  come  in  direct  contact  with 
the  material  to  be  calcined,  but  the  fuel  is  separated  from  it.  The 
simplest  and  most  common  form  is  shown  in  Fig.  11.  The  fire 
burns  on  the  grate  at  (G),  and  the  flames,  passing  over  the  bridge  at 
(E),  are  deflected  downward  by  the  low  sloping  roof  of  the  furnace, 
and  pass  directly  over  the  surface  of  the  charge  in  the  bed  of  the 


FIG.  11. 


furnace  at  (B),  finally  escaping  through  the  throat  (F)  into  the 
chimney.  The  charge  is  spread  out  in  a  thin  layer  on  the  bed  (B), 
and  may  be  either  oxidized  or  reduced  according  to  the  method  of 
firing  and  the  amount  of  air  admitted. 

The  revolving  furnace  (Figs.  3  and  39)  is  a  very  important  modi- 
fication of  the  reverberatory  furnace.  This  consists  of  a  horizontal 
or  slightly  inclined  cylinder  (B)  of  iron  or  steel  plates,  lined  with 
fire-brick  or  other  suitable  fire-resisting  material,  and  open  at  each 
end.  The  flames  from  a  grate  (A)  at  one  end  pass  through  it  on 
their  way  to  the  chimney  (D).  The  cylinder  is  revolved  about  its 
longitudinal  axis  by  means  of  a  gear.  It  is  turned  until  a  man- 


18  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

hole  in  the  side  is  brought  directly  under  a  hole  in  the  floor  above, 
the  bolted  cover  is  removed,  and  the  charge  dumped  in.  The  revo- 
lution of  the  cylinder  stirs  the  charge  thoroughly,  and  brings  it  into 
intimate  contact  with  the  flame.  To  discharge  the  contents,  the 
cylinder  is  stopped  when  the  manhole  is  on  the  under  side,  the  cover 
is  removed,  and  the  material  drops  out  upon  the  floor  or  into  a  car 
placed  for  it.  To  facilitate  discharging,  the  lining  usually  slopes 
from  all  sides  towards  the  manhole.  The  speed  varies  from  about 
two  revolutions  a  minute  to  one  revolution  in  five  or  ten  minutes. 
These  furnaces  are  now  extensively  used,  their  advantages  being  the 
intimate  mixing  and  even  heating  of  the  charge,  and  the  large  quan- 
tities, amounting  often  to  several  tons,  which  can  be  worked  at  one 
time. 

Shaft  furnaces  and  kilns  are  of  two  general  classes,  periodic  and 
continuous.  After  a  charge  has  been  calcined,  the  periodic  furnace 
(p.  149)  or  kiln  is  allowed  to  cool  before  it  is  emptied  and  recharged. 
In  the  continuous  variety  (p.  148)  this  is  not  necessary,  and  the  cal- 
cined substance  is  withdrawn  and  fresh  material  added  without  loss 
of  time  or  waste  of  heat.  The  furnaces  may  be  charged  with  alter- 
nate layers  of  fuel  and  material  to  be  calcined.  By  this  method, 
known  as  "  burning  with  short  flame,"  the  material  to  be  calcined  is 
in  close  contact  with  the  fuel,  and  is  of  course  more  or  less  contami- 
nated with  ashes.  In  other  forms  of  shaft  furnaces  (Fig.  56)  the 
fuel  is  burned  on  a  separate  grate,  and  only  the  flames  and  hot  gases 
pass  into  the  shaft ;  consequently,  no  ashes  are  left  in  the  product. 
This  process  is  called  "  burning  with  long  flame.'7 

Any  of  the  various  forms  of  furnace  here  mentioned  may  be 
heated  by  natural  gas,  generator  gas,  or  oil.  This  is  very  advanta- 
geous in  the  matter  of  cleanliness  and  of  regularity  of  temperature. 
(See  Fuels.) 

REFRIGERATION 

Since  refrigerating  machines  have  made  artificial  cooling  of 
rooms  and  of  material  possible,  industries  which  were  formerly  only 
carried  on  in  cold  weather  are  now  operated  at  all  seasons.  The 
manufacture  of  ice  is  also  a  large  and  increasing  industry,  and  is 
apparently  forcing  the  natural  product  from  the  market  more  and 
more  each  year. 

The  principle  involved  in  a  refrigerating  machine  is  the  rapid 
absorption  of  heat  by  the  rapid  evaporation  of  a  volatile  liquid. 
The  substances  most  used  are  liquefied  ammonia,  sulphur  dioxide, 
carbon  dioxide,  and  the  very  volatile  liquids  derived  from  petroleum, 


INTRODUCTION 


19 


chiefly  cymogene  and  rhigolene.     In  this  country  at  least  by  far  the 
greatest  number  of  machines  employ  liquid  ammonia. 

The  gas  is  heavily  compressed  and  then  liquefied  by  passing  it 
into  a  coil  over  which  a  large  amount  of  cold  water  flows  ;  the  liquid 
is  then  forced  through  a  small  opening  into  a  large  chamber  or  coil 
of  pipe,  from  which  the  gas  formed  may  be  rapidly  exhausted  by  a 
pump.  The  rapid  expansion  and  conversion  of  the  liquid  to  a  vapor 
here  absorbs  much  heat  from  the  walls  of  the  coil  or  chamber, 
whose  temperature  consequently  falls  considerably  below  the  freez- 
ing point  of  pure  water.  In  order  to  increase  the  external  surface 


EXPANSION 
COCK* 


FIG.  12. 


of  the  expansion  coils,  cast-iron  disks  are  placed  at  frequent  inter- 
vals on  the  pipe  perpendicular  to  its  line  of  direction.  Only  a 
comparatively  small  amount  of  ammonia  or  other  volatile  liquid  is 
necessary  for  the  continuous  working  of  the  machine.  Since  the  gas 
is  returned  to  the  compressor,  it  is  only  necessary  to  supply  that  lost 
by  leakage. 

It  is  often  customary  to  surround  the  expansion  coils  with  a 
brine  or  calcium  chloride  solution,  which  is  then  pumped  through 
coils  or  pipes  in  rooms  to  be  cooled.  For  making  ice,  galvanized  iron 
boxes  are  filled  with  water  and  immersed  in  the  cold  brine. 

In  the  system  shown  in  the  diagram  (Fig.  12)  a  certain  amount 
of  oil  is  injected  into  the  compressor  along  with  each  charge  of 


20  OUTLINES  OF   INDUSTRIAL   CHEMISTRY 

ammonia.  This  insures  complete  emptying  of  the  compressor  at 
each  stroke,  lubricates  the  piston,  prevents  the  gas  escaping  behind 
the  piston,  and  absorbs  part  of  the  heat  evolved  in  the  cylinder  by 
the  compression  of  the  gas.  This  oil  is  separated  from  the  liquefied 
ammonia  by  gravity  in  separating  tanks  and  returned  to  the  com- 
pressor. 

The  machines  above  described  are  called  "compression  ma- 
chines," because  the  volatile  substance  is  compressed  directly  to  be 
used  again.  Another  class  of  refrigerating  apparatus  depends  for 
the  recovery  of  the  volatile  substance  upon  absorption  of  the  vapors 
in  some  liquid  from  which  they  can  again  be  set  free.  The  cooling 
effect  in  this  case  is  also  produced  by  rapid  evaporation  of  the 
liquefied  gas,  the  difference  in  the  two  classes  of  machines  being  in 
the  method  of  recovering  the  vaporized  liquid  for  use  again.  In 
the  Carre  ammonia  absorption  apparatus  very  concentrated  aqua 
ammonia  is  heated  in  a  closed  iron  retort,  connected  with  another 
iron  vessel  which  is  surrounded  by  cold  water.  The  ammonia  vapor 
driven  out  of  solution  by  the  heat  passes  into  this  vessel,  where  it  is 
liquefied  by  its  own  pressure.  The  retort  containing  the  water  from 
which  the  ammonia  has  been  expelled  is  then  rapidly  cooled  by  sub- 
merging in  a  tank  of  cold  water.  A  reabsorption  of  the  ammonia 
vapors  by  the  water  in  the  retort  then  takes  place,  and  owing  to  the 
decrease  of  pressure  the  liquefied  ammonia  in  the  receiver  is  evapo- 
rated rapidly ;  heat  is  absorbed  from  substances  in  contact  with  the 
receiver  walls,  and  thus  water  may  be  frozen.  Another  style  of 
absorption  machine  evaporates  water  in  a  vacuum  apparatus,  and 
absorbs  the  vapor  in  concentrated  sulphuric  acid.  The  dilute  acid 
thus  produced  is  concentrated  in  open  pans  by  evaporating  the 
water,  and  is  used  again. 

The  absorption  machines  are  not  readily  adaptable  to  the  cooling 
of  salt  solutions,  and  hence  are  not  used  for  chilling  rooms.  They 
also  require  a  larger  quantity  of  cooling  water,  and  are  generally 
more  complicated  and  expensive  than  the  compression  machines. 

A  third  class  of  machines  are  those  depending  on  the  sudden  ex- 
pansion of  highly  compressed  air  or  other  gas,  which  does  not  liquefy 
at  the  temperature  and  pressure  used.  These  machines  are  large 
and  complicated  and  are  not  adapted  to  making  ice,  but  find  limited 
use  for  cooling  and  ventilating  storage  buildings,  especially  where 
any  traces  of  ammonia  or  other  vapor  would  injure  the  contents. 


INTRODUCTION  21 


DENSITY 

By  density  or  specific  gravity  of  a  liquid  is  meant  its  relative 
weight  compared  with  the  weight  of  an  equal  volume  of  pure  water 
at  a  definite  temperature.  The  determination  of  density  is  one  of 
the  most  frequent  operations  in  chemical  work.  This  may  be  done 
with  a  pykiiometer  when  very  exact  results  are  required,  but  in 
technical  operations,  sufficient  accuracy  for  all  practical  purposes 
may  be  attained  by  the  hydrometer.  This  is  usually  a  glass  instru- 
ment, consisting  of  a  cylindrical  bulb,  weighted  at  the  lower  end, 
and  drawn  out  at  the  upper  end  to  a  long,  slender  tube,  carrying  a 
scale.  The  gradations  of  the  scale  begin  at  the  top  and  read  down- 
ward, the  numerically  greater  reading  being  at  the  bottom,  except  in 
one  instance,  —  that  of  Baume's  scale  for  liquids  lighter  than  water. 
Since  the  density  of  a  liquid  varies  as  its  temperature  changes,  the 
scale  is  adjusted  to  a  certain  temperature,  usually  about  15°  C.,  at 
which  determinations  must  be  made. 

When  the  hydrometer  is  placed  in  a  liquid,  it  sinks  sufficiently 
to  displace  a  volume  of  the  liquid  equal  in  weight  to  the  weight 
of  the  instrument,  and  floats  in  an  upright  position.  Should  the 
hydrometer  sink  so  deeply  into  the  liquid  that  the  scale  is  entirely 
below  the  surface,  the  density  is  less  than  the  spindle  is  intended  to 
measure,  and  one  having  lower  *  numerical  readings  should  be  used. 
If,  on  the  contrary,  the  spindle  does  not  sink  deep  enough  to  bring 
the  scale  into  the  liquid,  an  instrument  having  higher  numerical 
scale  readings  is  necessary. 

Three  systems  of  hydrometer  scales  are  in  common  use,  besides 
a  great  number  of  special  scales  intended  to  give  one  particular 
factor  in  the  density  of  a  liquid ;  e.g.  the  per  cent  of  alcohol  in  a 
mixture  of  alcohol  and  water,  or  the  amount  of  sugar  in  a  syrup,  etc. 

The  direct  specific  gravity  hydrometer  is  so  constructed  that 
the  reading  on  its  scale  shows  the  density  of  the  liquid  directly  as 
compared  with  pure  water  at  the  same  temperature  (15°  C.).  Its 
scale  is  adapted  to  liquids  heavier  or  lighter  than  water.  The  point 
to  which  it  sinks  in  pure  water  at  15°  C.  is  marked  1.000.  As  usually 
furnished,  a  set  of  these  hydrometers  consists  of  four  spindles,  the 
scale  being  thus  divided  into  four  sections.  The  first  spindle,  with 
gradations  from  0.700  to  1.000,  is  for  liquids  lighter  than  water,  and 
the  others  are  for  those  heavier  than  water.  The  scale  is  usually 

*  Baume's  hydrometer  for  liquids  lighter  than  water  is  an  exception  (p.  22). 


22  OUTLINES   OF  INDUSTRIAL   CHEMISTRY 

divided  about  as  follows :  1.000  to  1.300  on  the  second  spindle,  1.300 
to  1.600  on  the  third,  and  1.600  to  2.000  on  the  fourth. 

The  gradations  at  the  top  of  each  spindle  are  further  apart  than 
those  at  the  bottom  of  the  stem,*  rendering  the  reading  somewhat 
more  difficult  in  dense  liquids  than  in  those  of  lighter  gravity. 

Twaddell's  hydrometer  is  also  a  direct  reading  instrument.  The 
system  consists  of  a  series  of  spindles  (usually  six  in  number)  car- 
rying gradations  from  0  to  174.  The  reading  in  pure  water,  at 
15.5°  C.,  is  taken  as  0,  and  each  subsequent  rise  of  0.005  sp.  gr.  is 
recorded  on  the  scale  as  one  additional  division.  Thus  10  Twaddell 
becomes  1.050  sp.  gr.  The  gradations  on  this  scale  are  also  closer 
together  as  the  density  increases,  but  as  its  total  length  is  divided 
among  six  spindles,  the  readings  are  not  so  difficult  even  at  the 
highest  densities.  The  instruments  are  small,  the  gradations  on 
each  stem  occupying  about  three  linear  inches,  so  that  it  may  easily 
be  used  in  an  ordinary  100  cc.  measuring  cylinder.  For  the  reasons 
that  it  is  easy  to  read,  requires  but  a  small  quantity  of  liquid  to  be 
tested,  and  permits  a  ready  conversion  of  its  readings  into  specific 
gravity  by  a  very  simple  calculation,  this  is  the  most  convenient 
hydrometer  for  ordinary  factory  or  laboratory  use.  It  is,  however, 
not  adapted  to  liquids  lighter  than  water. 

Twaddell'readings  are  converted  into  specific  gravity  as  follows: 
Multiply  the  reading  by  .005,  and  add  1.000  to  the  product.  Thus  15 
Twaddell  becomes  1.075  sp.  gr.  (1.000  +  [15  x  .005]  =  1.075.) 

Baume's  hydrometer  is  a  very  unscientific  instrument,  but  is 
largely  used  in  technical  work.  Its  readings  bear  no  very  direct 
relation  to  true  specific  gravity.  Baume  dissolved  15  parts"of  pure 
salt  in  85  parts  of  pure  water  at  12.5°  C.  The  point  to  which  his 
instrument  sank  in  this  solution  was  marked  15 ;  the  point  to  which 
it  sank  in  pure  water  was  marked  0.  The  distance  between  these 
points  was  divided  into  fifteen  equal  parts,  and  the  entire  stem  marked 
off  in  divisions  of  this  width.  This  produced  an  instrument  for 
liquids  heavier  than  water. 

For  liquids  lighter  than  water,  the  point  to  which  the,  instrument 
sank  in  a  10  per  cent  solution  of  salt  was  marked  0,  and  that  to 
which  it  sank  in  distilled  water  was  marked  10,  the  distance  between 
these  points  was  divided  into  10  equal  parts,  and  this  gradation  con- 
tinued the  entire  length  of  the  spindle.  The  0  thus  being  placed  at 
the  bottom  of  the  stem,  the  lighter  the  gravity  of  the  liquid  tested, 

*  For  the  explanation  of  this  fact  consult  any  of  the  larger  works  on  physics. 


INTRODUCTION  23 

the  greater  numerically  is  the  reading  of  the  scale.  For  instance,  a 
liquid  reading  70  Be.  is  of  less  density  than  one  of  50  Be.,  which  in 
turn  is  lighter  than  water  at  10  Be. 

To  further  complicate  matters,  the  instrument  makers  appear  to 
have  become  confused,  and  produced  instruments  with  erroneous 
scales.  A  test  made  a  few  years  ago  disclosed  thirty-four  different 
scales,  none  of  which  were  correct !  * 

The  conversion  of  Baume  readings  to  specific  gravity  involves 
some  calculation  and  is  usually  accomplished  by  reference  to  tables. 
The  formulae  for  this  conversion  are  as  follows :  — 

«  _        144.3       (for  liquids  heavier  than  water.     Tempera- 

~  144.3  -  Be.      ture  15°  C.).f 

ST>  PT  =        140          (for  liquids  lighter  than  water.     Tempera- 
"130  + Be.        ture  17.5°  C.). 

The  pyknometer  is  not  very  often  used  in  technical  work,  but 
a  brief  description  of  it  may  not  be  out  of  place  here.  It  consists 
of  a  small  bottle,  having  ground  into  its  neck  a  capillary  tube 
enlarged  at  its  upper  end,  to  form  a  reservoir  which  is  closed  by  a 
stopper.  The  tube  is  removed  and  the  bottle  filled  with  the  liquid 
to  be  tested;  the  tube  is  then  inserted  tightly,  the  liquid  displaced 
rising  through  the  capillary  to  the  enlarged  part  of  the  tube.  The 
stopper  is  then  loosely  inserted  and  the  bottle  placed  in  a  bath  at 
the  temperature  at  which  the  density  is  to  be  taken.  When  the 
bottle  and  contents  have  reached  this  temperature  the  stopper  is 
taken  out  and  the  liquid  in  the  reservoir  removed  by  means  of 
absorbent  paper,  until  the  level  of  the  liquid  recedes  within  the 
capillary  to  a  mark  thereon.  The  stopper  is  then  tightly  inserted 
and  the  bottle  removed  from  the  bath,  and  after  cleaning  and  dry- 
ing its  outside,  allowed  to  stand  until  it  reaches  the  normal  tempera- 
ture of  the  room.  It  is  then  weighed,  and  the  density  of  the  liquid 
is  calculated  from  its  known  volume,  previously  determined  by  cali- 
bration of  the  bottle.  (For  determining  the  density  of  solids  by 
means  of  the  pyknometer,  see  T.  E.  Thorpe's  Dictionary  of  Applied 
Chemistry,  Vol.  III.,  p.  528.) 

Westphal's  balance  is  a  special  form  of  balance  for  determining 
the  density  of  liquids.  A  glass  plummet  of  known  weight  and 
volume  is  suspended  from  the  beam  by  a  fine  platinum  wire,  and 

*C.  F.  Chandler,  Proc.  Nat.  Acad.  Sciences,  1881. 

t  Alkali-makers'  Handbook  (Lunge  and  Hurter),  p.  175. 


24  OUTLINES  OF  INDUSTRIAL  CHP]MISTRY 

is  submerged  in  the  liquid  to  be  tested.  The  weight  which  the 
plummet  loses  by  this  submersion  is  the  weight  of  the  volume  of 
liquid  it  displaces.  The  characteristic  feature  of  the  instrument  is 
the  decimal  graduation  of  the  beam,  with  the  use  of  riders  of  0.1, 
0.01,  and  0.001  part  of  the  weight  of  the  water  displaced  by  the 
plummet.  This  permits  the  actual  specific  gravity  to  be  at  once 
read  off  on  the  beam,  as  soon  as  the  latter  has  been  brought  to 
equilibrium  with  the  plummet  suspended  in  the  liquid  in  question. 


FUELS. 

Fuels  are  substances  which,  when  burned  with  air,  evolve  heat 
with  sufficient  rapidity  and  in  sufficient  quantity  to  be  employed 
for  domestic  or  industrial  purposes. 

There  are  three  classes  of  fuel :  solid,  liquid,  and  gaseous.  In  the 
majority  of  these  the  essential  constituent  is  carbon,  but  in  many  of 
them  hydrogen  is  also  an  important  ingredient.  In  rare  cases  sul- 
phur, phosphorus,  silicon,  or  manganese  may  take  part  in  the  com- 
bustion; but  for  the  purposes  for  which  fuel  is  ordinarily  used  these 
constituents  are  deleterious.  Oxygen  is  sometimes  regarded  as 
advantageous,  but  not  always.  Nitrogen  may  cause  a  direct  loss  of 
calorific  power,  owing  to  its  dilution  of  the  combustible  gases,  but 
in  most  solid  fuels  the  percentage  of  nitrogen  is  so  small  that  its 
effect  is  negligible. 

SOLID   FUELS 

The  solid  fuels  are  wood  and  other  matter  containing  cellulose, 
peat,  lignite  or  brown  coal,  bituminous  coal,  anthracite,  charcoal,  and 
coke. 

Wood  consists  of  cellulose  (C6H1005)W,  resins,  lignine,  various 
inorganic  salts,  and  water.  The  quantity  of  water  present  has 
great  effect  on  the  heating  value  and  ranges  from  25  to  50  per 
cent  in  green  wood,  and  from  10  to  20  per  cent  in  air-dried  wood. 
Wood  cut  in  the  spring  and  summer  contains  more  water  than  that 
cut  in  the  early  part  of  the  winter.  A  cord  of  hard  wood,  such  as 
ash  or  maple,  is  about  equal  in  heating  value  to  one  ton  of  bitumi- 
nous coal ;  soft  woods,  such  as  pine  and  poplar,  have  less  than  half 
this  amount.  Wood  burns  with  a  long  flame  and  makes  compara- 
tively little  smoke;  but  its  calorific  intensity  is  low,  averaging 
from  3000  to  4000  C.  per  kilo  of  air-dried  wood.  It  is,  however, 
easily  kindled,  the  fire  quickly  reaches  its  maximum  intensity,  and 


FUELS  25 

a  relatively  small  quantity  of  ash  is  formed.  Wood  is  too  expensive 
for  industrial  use,  except  in  a  few  special  cases,  where  freedom  from 
dirt  and  smoke  is  necessary. 

Of  other  cellulose  materials,  shavings,  sawdust,  and  straw  are 
used  for  fuel  in  some  places.  They  are  bulky  and  difficult  to  handle, 
while  their  heat  value,  which  depends  on  the  amount  of  moisture 
they  contain,  is  seldom  more  than  from  one-third  to  one-half  that 
of  good  coal.  Such  waste  matter  as  spent  tan-bark  and  begasse 
(crushed  sugar  cane),  and  the  pulp  from  sugar  beets  is  sometimes 
used  for  fuel  for  evaporation  or  for  steam,  but  owing  to  the  large 
amount  of  moisture  they  contain,  the  heat  value  is  very  low. 

Peat  is  the  product  of  slow  decay  of  mosses,  especially  Spliag- 
nacece,  under  water.  It  is  of  little  importance  in  this  country,  but 
is  extensively  used  in  parts  of  Europe  where  it  is  found.  Since  it 
contains  a  large  amount  of  water  and  inorganic  matter,  its  calorific 
power  is  not  high,  averaging  from  '3000  to  4000  C.  per  kilo.  It  is 
dug  from  the  bogs  and  dried  in  the  air,  sometimes  being  heavily 
compressed  to  reduce  its  bulk.  As  thus  prepared,  it  contains  from 
15  to  20  per  cent  of  moisture  and  from  8  to  12  per  cent  ash.  It  is 
used  considerably  as  a  packing  material,  owing  to  its  soft  and  spongy 
consistency. 

Lignite  or  brown  coal  is  intermediary  between  peat  and  bitu- 
minous coal.  It  was  probably  formed  from  swamp  plants  which 
decomposed  under  water,  and  is  geologically  of  more  recent  forma- 
tion than  true  coal.  It  is  dark  brown  or  black  in  color,  and  its 
texture  is  fibrous,  earthy,  or  sometimes  vitreous.  It  usually  con- 
tains from  15  to  20  per  cent  of  moisture,  a  large  quantity  of  ash,  and 
often  a  considerable  amount  of  sulphur.  It  burns  freely  with  a 
long  flame,  producing  much  smoke,  and  its  calorific  power  varies 
from  4000  to  5500  C.  It  is  extensively  used  for  heating  steam 
boilers  and  evaporating  pans,  and  for  domestic  fires. 

Bituminous  coal  is  the  most  important  of  all  fuels.  There  is 
a  great  variety  in  the  kinds  of  coal  classed  under  this  name,  but 
they  differ  chiefly  in  the  amount  of  volatile  matter,  which  ranges 
from  20  to  50  per  cent.  They  were  all  formed  from  similar  sources, 
the  varieties  having  resulted  from  pressure  and  from  exposure  to 
heat.  The  specific  gravity  varies  from  1.25  to  1.75.  They  are  clas- 
sified according  to  their  behavior  when  burning,  as  fat,  caking,  and 
non-caking.  Fat  coals  usually  have  a  dull  lustre,  are  very  rich  in 
volatile  matter,  sometimes  containing  as  much  as  50  per  cent,  and 
burn  with  a  long,  smoky  flame,  sometimes  caking  in  the  fire.  Non- 
caking  coals  are  those  which  burn  freely,  with  little  smoke,  and  do 


26  OUTLINES  OF   INDUSTRIAL   CHEMISTRY 

not  cake.     The  caking  coals  burn  with  a  smoky  flame  and  fuse  or 
sinter  together. 

The  formation  of  coal  is  probably  due  to  a  slow  decomposition 
of  cellulose  matter,  under  fresh  water,  by  which  marsh  gas  (CH4)  and 
carbon  dioxide  (C02)  were  eliminated.  The  composition  of  a  typi- 
cal coal,  as  shown  by  the  analysis  of  good  samples,  may  be  repre- 
sented by  the  symbol  (CJH.x£)2),  and  assuming  this,  the  change  of 
cellulose  may  be  represented  by  the  equation  :  — 

6  (C6H1005)  =  3  CH4  +  7  C02  +  14  H2O  +  C^O* 

Various  changes  were  afterwards  brought  about  by  the  heat  and 
pressure  within  the  earth's  strata,  and  the  character  of  the  coals 
modified  in  many  cases.  Thus,  more  or  less  of  the  volatile  constit- 
uents were  removed,  and  the  coal  itself  compressed  to  a  very  hard, 
compact  mass.  When  this  process  went  to  the  extreme,  nearly  the 
whole  of  the  volatile  constituents  were  expelled,  and  the  resulting 
product  is  the  hard  coal  known  as  anthracite. 

Anthracite  coals  are  nearly  pure  carbon,  are  very  hard  and  dense, 
have  a  very  high  lustre,  and  contain  but  little  hydrogen  or  volatile 
matter.  They  burn  with  a  slight  flame,  form  no  smoke,  have  no 
caking  properties,  and  are  difficult  to  ignite.  Their  specific  gravity 
is  high,  being  nearly  1.75  in  good  Lehigh  coal.  They  have  a  calorific 
value  of  from  9000  to  9500  C. 

Between  bituminous  and  anthracite  coals  are  a  number  of  semi- 
anthracites,  which  cannot  be  classed  in  either  variety. 

Coal  deteriorates  considerably  when  stored,  owing  to  the  escape 
of  some  of  its  volatile  constituents.  There  is  a  popular  idea  that 
wetting  coal  before  burning  increases  its  heating  capacity  ;  but  this 
is  a  fallacy,  for  a  loss  of  heat  results. 

The  average  composition  of  various  coals  is  here  tabulated  for 
comparison  :  — 


Brown  coal     ......  1.30  20.9  50.9  10.2  18* 

Bituminous  coal  (W,  Va.)    .  -  23.96  67.32  8.72  —  t 

Steam  coal  (Cumberland)     .  1.33  15.13  74.53  10.34  .  —  t 

Anthracite  (Pa.)     ....  1.56  6.89  91.64  1.47  —  t 

Anthracite  (R.I.)    .     ,-Vv  1.85  10.50  85.84  3.66  —  t 

Charcoal  is  made  by  the  dry  distillation  of  wood,  at  a  tempera- 
ture of  from  400°  to  450°  C.     This  is  done  in  heaps,  or  in  closed 

*  Gas  and  Fuel  Analyses  for  Engineers,  A.  H.  Gill,  p.  43. 
t  Fuels,  Mills  and  Rowan. 


FUELS 


27 


retorts.  All  the  volatile  matter  is  driven  off,  and  the  residue  con- 
sists of  carbon  and  the  inorganic  constituents  of  the  wood.  Good 
charcoal  is  porous,  brittle,  with  conchoidal  fracture,  and  retains  the 
form  of  the  wood,  but  has  only  about  three-fourths  of  the  volume 
and  usually  about  20  per  cent  of  the  weight  of  wood.  It  burns  with 
but  slight  flame,  without  smoke,  and  is  easily  ignited.  Containing 
but  little  sulphur  or  phosphorus,  it  is  especially  useful  in  making 
some  high  grades  of  iron  and  steel.  Its  calorific  intensity  is  about 
7000  C. 

In  this  country  the  most  of  the  charcoal  is  made  by  burning  wood 
in  "charcoal  pits."  The  wood  is  heaped  in  a  hemispherical  pile 
around  a  central  opening,  and  covered  with  earth  and  sod,  leaving 
only  a  few  small  draught  holes  near 
the  bottom.  Then  it  is  ignited  at  the 
centre  and  allowed  to  burn  until  the 
whole  pile  is  on  fire.  A  smoulder- 
ing combustion  takes  place,  largely 
at  the  expense  of  the  oxygen  and 
hydrogen  of  the  wood  fibre,  forming 
water,  carbon  dioxide  and  volatile 
hydrocarbons,  which  escape.  The 
draught  holes  are  then  all  closed 
and  the  pit  is  kept  carefully  covered 
until  the  fire  smothers  and  the  char- 
coal is  cold.  By  carbonizing  in  pits 
nearly  all  the  volatile  matter  is  lost, 
or  at  best,  only  a  part  of  the  tar  is 
saved  and  the  yield  of  charcoal  is 
only  20  per  cent  by  weight  of  the 
wood.  But  if  the  process  is  carried 
on  in  retorts,  a  large  amount  of  gas, 
pyroligneous  acid,  and  tar  is  col- 
lected (see  p.  257),  and  about  30  per 
cent  of  charcoal  is  obtained,  together  with  nearly  40  per  cent  of 
pyroligneous  acid  and  4  per  cent  of  tar. 

Coke  is  made  by  the  destructive  distillation  of  coal.  It  has  a 
silvery  white  lustre,  an  open,  porous  structure,  and  a  metallic  ring 
when  struck.  It  contains  all  the  ash-forming  materials  of  the  coal, 
but  nearly  all  volatile  matter  and  sulphur  have  been  eliminated. 
For  metallurgical  purposes  it  must  be  sufficiently  strong  to  sustain 
the  weight  of  the  charge  in  the  furnace  without  crushing.  The 
calorific  value  is  from  8000  to  8500  C.  It  burns  without  smoke  and 


FIG.  13. 


OF  THK 
-T  TTTT — '-r*fc  / 


28 


OUTLINES  OF  INDUSTRIAL   CHEMISTRY 


with  but  little  flame,  and  does  not  cake.  It  is  made  in  kilns  of  two 
general  types:  —  The  "bee-hive"  coke  oven  (Fig.  13)  is  made  of 
brick,  with  a  circular  opening  (A)  at  the  top  and  a  door  (B)  at  the 
side,  through  which  the  coke  is  drawn.  A  part  of  the  coal  is  burned, 
in  order  to  carbonize  the  remainder.  As  a  rule,  no  attempt  is  made 
to  save  the  volatile  products  or  the  tar.  The  yield  of  coke  amounts 
to  only  60  or  65  per  cent  of  the  weight  of  the  coal. 

Coking  ovens  in  which  the  by-products  are  saved,  are  much  used 
in  Germany,  and  to  a  slight  extent  in  this  country.  There  are  sev- 
eral kinds,  but  the  Otto-Hoffmann,  the  Simon-Carves,  and  the  Semet- 
Solvay  ovens  are  most  used.  In  these,  the  ammonia  and  coal  tar  are 
recovered,  and  a  coke  suitable  for  metallurgical  purposes  is  obtained. 
The  waste  gas  is  employed  to  heat  the  retorts. 


i  MI  nnnnn-nnnnnnnnpnnnnnnnnnnnnnryrir 

liliiiS^^ 


:^;*?£S* 


.-  .,'-.'.'.•,-; '-^ 


FIG.  14. 


The  Otto-Hoffmann  oven  is  shown  in  Fig.  14.  The  retorts  are 
narrow  chambers  (0)  about  30  feet  long,  5  feet  high,  and  22  inches 
wide,  having  doors  at  each  end,  and  heated  by  vertical  flues  (T,  T) 
in  the  walls.  Coal  is  charged  through  (F,  F),  while  the  gases  and 
tar  pass  off  through  (A,  A)  to  the  hydraulic  main  (V,  V).  The  gas 
for  heating  enters  from  pipe  (G),  mixes  with  hot  air  from  the  re- 
generator (R),  and  burns  in  the  flue  (S)  under  the  retorts,  the  flame 
passing  up  through  the  flues  (T,  T),  and  down  through  (T',  T')  to 
(S'),  from  which  the  products  of  combustion  pass  through  the  regen- 
erator (Rr)  and  heat  it.  After  a  time,  the  flow  of  gases  is  reversed, 
the  producer  gas  enters  through  (Gf),  and  air  through  (R'),  burning 
together  in  (S'),  while  the  products  of  combustion  escape  through 
(R).  The  volatile  matter  given  off  from  the  coal,  passes  through 
(V)  to  washers  and  scrubbers  (see  Illuminating  Gas),  which  remove 
tar  and  ammonia,  while  the  gas  is  stored  in  a  holder,  to  be  led,  later, 
through  (G,  G'),  and  burned  under  the  retorts. 


FUELS 


29 


The  Simon-Carves  oven  (Fig.  15)  is  also  a  long,  narrow  retort  (A) 
with  doors  at  each  end,  but  the  heating  flues  (F,  F)  are  set  hori- 
zontally in  the  retort  walls.  The  volatile  matter  escapes  from  the 
retort  through  (B),  passes  to  the  washer  and  scrubber,  whence  the 
purified  gas  goes  to  the  holder,  from  which  it  is  drawn  as  needed, 
through  (G),  and  burned  with  hot  air. 


FIG.  15. 


The  Semet-Solvay  oven  (Fig.  16)  also  has  horizontal  flues,  but 
deeper  and  narrower  retorts  than  the  two  just  mentioned.  Each 
retort  has  an  independent  set  of  flues  which  are  placed  in  the  retort 


A  -  Charging  Holes  D  -  Chimney  Canal 

B  -  Gas  uptake  p  .  Heating  Flues 

C  -  Gas  Inlet  to  Heating  Flues    R  -  Wall  between  Retorts 

FIG.  16. 

lining  and  backed  by  a  heavy  brick  retaining  wall ;  this  supports  the 
weight  of  the  roof  arch,  and  also  holds  the  heat  during  the  drawing 
and  charging  of  the  retort.  Thus  the  flue  walls  can  be  made  much 
thinner  than  in  the  ovens  previously  mentioned,  and  the  oven  works 
more  rapidly,  giving  a  larger  yield  of  coke,  and  will  coke  coals  which 
are  low  in  volatile  matter.  The  lining  can  easily  be  replaced  with- 
out rebuilding  the  entire  oven.  The  retorts  are  usually  about  30 


30  OUTLINES  OF  INDUSTRIAL   CHEMISTRY 

feet  long  by  16  inches  wide,  and  5J  feet  deep,  and  hold  about  4}- 
tons  of  coal  at  each  charge.  No  regenerative  heating  is  used,  the 
heat  being  retained  in  the  walls  between  the  retorts.  A  number  of 
these  ovens  have  been  recently  introduced  into  this  country  and 
give  excellent  results. 

LIQUID   FUELS 

The  most  important  liquid  fuels  are  crude  petroleum,  and  various 
oily  residues  obtained  in  distilling  petroleum,  shale  oil  and  coal  tar. 

Crude  petroleum  and  the  residuum  from  the  manufacture  of  burn- 
ing oils  and  lubricators,  are  the  chief  sources  in  this  country.  The 
residuum  from  Russian  petroleum,  called  "  astatki"  is  very  exten- 
sively used  in  southern  Russia. 

Crude  petroleum  is  easily  regulated  so  as  to  burn  without  smoke 
or  soot,  giving  a  steady  heat  and  requiring  no  stoking.  It  is  less 
bulky,  and  from  two  to  two  and  a  half  times  as  efficient  as  anthra- 
cite coal.  Its  calorific  intensity  is  about  20,000  C.,  and  it  evaporates 
about  16  Ibs.  of  water  to  one  pound  of  oil.  One  pound  of  coal-tar 
residue  evaporates  13  Ibs.  of  water. 

Liquid  fuel  is  coming  into  more  general  use  every  year,  espe- 
cially where  long  flame  and  high  temperature  are  desired.  It  is 
usually  burned  as  spray,  being  forced  into  the  furnace  by  a  large 
atomizer  supplied  with  an  air  blast  or  superheated  steam. 

GASEOUS   FUELS 

Gaseous  fuels  may  be  divided  into  four  classes :  natural  gas, 
producer  gas,  water  gas  and  coal  gas. 

Natural  gas  exists  already  formed  in  the  earth,  and  is  obtained 
by  boring  tube  wells,  similar  to  petroleum  wells.  Its  essential  heat- 
producing  constituents  are  methane  (CH4)  and  hydrogen.  It  is  the 
cheapest  and  most  efficient  of  all  fuels,  when  properly  burned ;  but 
it  requires  a  large  amount  of  air  for  its  combustion,  and  special 
burners  must  be  used. 

Producer  gas  is  made  by  forcing  air  through  a  bed  of  incan- 
descent coal  or  coke,  in  specially  constructed  furnaces.  Its  essential 
heat  constituent  is  carbon  monoxide  (CO),  of  which  it  contains 
about  28  to  30  per  cent.  But  it  also  contains  about  63  per  cent  of 
nitrogen  from  the  air,  and  some  carbon  dioxide,  which  dilute  the 
gas  very  much,  and  reduce  its  calorific  intensity  greatly.  It  is 
extensively  used  for  fuel,  because  of  its  cheapness,  cleanliness,  and 
the  regularity  of  the  temperature  obtained. 


FUELS 


31 


In  converting  carbon  to  carbon  monoxide,  about  one-third  of 
the  heat  value  of  the  carbon  is  set  free,  thus  heating  the  gas  very 
hot.  If  it  is  at  once  led,  through  short  flues,  into  the  combustion 
chamber  and  burned  with  air,  a  much  higher  temperature  is  ob- 
tained, than  if  it  is  permitted  to  cool  before  burning.  In  modern 
gas  producers,  this  waste  of  heat  is  largely  avoided  by  introducing 
steam  into  the  incandescent  coal,  together  with  the  air ;  the  steam 
dissociates  into  hydrogen  and  oxygen,  and  the  latter  gas  combines 
with  the  carbon,  forming  more  carbon  monoxide.  These  gases, 
mixing  with  the  producer  gas,  increase  its  calorific  intensity. 


FIG.  17. 


FIG.  18. 


In  the  Siemens  gas  producer*  (Fig.  17),  the  coal  is  introduced 
at  (E),  falls  upon  the  step  grate  (B,  B),  and  is  brought  to  incan- 
descence by  air  entering  through  the  openings  while  steam  is  injected 
from  the  pipe  (C),  and  the  gas  formed  escapes  through  (A,  A).  The 
ashes  fall  through  the  grate  (G)  into  the  pit,  which  is  kept  closed 
except  when  cleaning.  A  more  modern  producer  (Taylor's)  is  shown 
in  Fig.  18.  The  coal  rests  on  a  bed  of  ashes  (A,  A),  and  air  is  forced 
through  the  blast  pipe  (F),  raising  the  fuel  to  incandescence.  The 
gas  formed  passes  out  by  the  pipe  (E).  The  grate  (G)  is  made  to 
revolve  by  the  crank  at  (B),  and  the  ashes  fall  over  the  edge  of  the 
grate  at  (H).  The  bed  of  ashes  is  kept  about  3  feet  deep  on  the 
revolving  bottom  at  all  times.  Steam  from  the  pipe  (D)  is  intro- 

*  Jour.  Soc.  Chem.  Industry,  1885,  441. 


32 


OUTLINES  OF   INDUSTRIAL   CHEMISTRY 


duced  with  the  air  through  the  blast  pipe,  which  is  provided  with 
a  hood  to  disseminate  them  through  the  fuel.  In  all  producer  gas 
plants,  the  regenerative  heating  system  is  used. 

The  Siemens  regenerative  furnace  is  a  type  of  this  style  of 
heating.  This  furnace  is  represented  in  its  simplest  form  in  Fig.  19. 
The  material  to  be  heated  is  placed  on  the  hearth  of  the  furnace 
(A).  There  are  four  passages,  B,  C,  D,  and  E,  filled  with  loosely 
piled  fire-brick  called  the  "checker  work."  On  their  way  to  the 
chimney,  the  hot  gases  from  the  furnace  pass  through  and  heat 
two  checker  works,  e.g.  (B)  and  (C).  When  they  are  sufficiently 
heated,  the  flow  of  furnace  gases  is  turned  into  (D)  and  (E),  through 
which  they  pass  to  the  chimney.  Then  fuel  gas  is  conducted 
through  the  hot  passage  (B),  to  the  furnace  (A),  where  it  mixes 


FIG.  19. 

with  air  which  has  been  heated  by  passing  through  (C).  The  tem- 
perature of  (A)  is  thus  much  higher  than  if  the  air  and  gas  arrived 
at  (A)  cold.  While  (B)  and  (C)  are  being  thus  cooled,  (D)  and  (E), 
are  being  heated  by  the  furnace  gases,  and  after  a  time,  the  dampers 
are  turned,  and  the  gas  made  to  pass  through  (E),  and  the  air 
through  (D),  while  the  combustion  products  pass  through  (B)  and 
(C)  to  the  chimney.  Hence  the  process  is  an  alternating  one,  the 
checker  works  on  one  side  being  heated,  while  those  on  the  other 
are  giving  up  their  heat  to  the  gas  and  air  respectively.  Since  the 
interstices  between  the  bricks  of  the  checker  work  frequently 
become  clogged  with  ashes  and  soot,  the  combustion  gases  are  some- 
times passed  through  flues  containing  narrow  tubes,  through  which 
the  gas  and  air  are  passing  to  the  furnace,  in  a  direction  opposite 
to  that  taken  by  the  fire  gases. 

The  waste  gases  from  blast  furnaces  contain  over  30  per  cent 


FUELS  33 

of  carbon  monoxide  and  about  63  per  cent  of  nitrogen.  These 
gases  are  largely  employed  near  the  furnaces  for  heating  purposes. 

Water  gas  is  sometimes  used  as  a  fuel,  but  oftener  as  a  con- 
stituent of  illuminating  gas  (p.  266).  It  is  made  by  blowing  steam 
over  incandescent  anthracite  coal  or  coke,  and  is  a  mixture  of  about 
45  per  cent  each  of  carbon  monoxide  and  hydrogen,  with  small 
amounts  of  nitrogen,  oxygen,  and  carbon  dioxide.  For  the  best  re- 
sults, the  temperature  must  not  fall  below  1000°  C. ;  above  this 
point,  the  reaction  is  :  — 

C  +  H20  =  2  H  +  CO. 

But  at  lower  temperatures,  the  following  takes  place :  — 
C  +  2  H20  =  C02  +  4  H. 

Fuel  water  gas  burns  with  a  pale  blue  or  colorless  flame,  without 
smoke  or  soot.  Its  calorific  value  is  about  3000  C.  per  cubic  meter. 
One  kilo  of  coke  produces  about  1.13  cubic  meters  of  water  gas,  but 
anthracite  gives  a  better  yield. 

The  fuel  is  brought  to  incandescence  by  a  blast  of  air,  and 
during  this  part  of  the  process  the  heat  generally  goes  to  waste. 
When  it  is  white  hot,  the  air  is  cut  off,  and  the  steam  is  turned  on ; 
decomposition  occurs,  according  to  the  first  reaction  above.  As 
soon  as  the  temperature  falls  below  1000°  C.,  the  steam  is  cut  off 
and  the  air  blast  turned  on  till  the  coal  is  again  white  hot.  Thus 
alternate  blowings  of  air  and  steam  are  carried  on.  The  generator 
gas  produced  by  the  air  blast  is  sometimes  saved  and  used,  but  in 
making  illuminating  gas  it  goes  to  waste.  For  illuminating  gas, 
this  water  gas  is  "  enriched  "  with  naphtha  (p.  266). 

Coal  gas  is  made  by  distilling  bituminous  coal  in  retorts  (p.  268). 
It  contains  hydrogen  and  marsh  gas  in  large  quantities,  —  about 
40  per  cent  of  each,  —  besides  small  amounts  of  carbon  monoxide, 
carbon  dioxide,  nitrogen,  oxygen,  and  hydrocarbons  of  the  CnH2w  and 
CnH2n_2  series,  which  impart  illuminating  properties.  It  has  a 
limited  use  in  domestic  stoves  and  as  a  source  of  power  in  gas 
engines. 

The  average  composition  of  the  various  fuel  gases  is  shown  in 
the  following  table  * :  — 

H        CH4       CO     C2H4    C02       N         O     H2S 
Natural  gas  (Ohio)  ...       2.2      92.6        0.5      0.3      0.3        3.6      0.3      0.2 

Coal  gas 47.0      40.5        6.0      4.0      0.5        1.5      0.5       — 

Water  gas 45.7        2.0      45.8       —      4.0        2.0      0.5       — 

Producer  gas 6.0        3.0      23.5       —      1.5      65.0       —       — 

*  Gas  and  Fuel  Analysis  for  Engineers,  A.  H.  Gill. 


34  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

When  burned  with  20  per  cent  excess  of  air,  and  assuming  that 
the  escaping  gases  have  a  temperature  of  500°  F.,  1000  cubic  feet 
of  gas  will  evaporate  the  following  number  of  pounds  of  water,  at 
from  GOT.  to  212°  F.:- 

Natural  gas 893  pounds  * 

Coal  gas 591      " 

Water  gas 262      " 

Producer  gas       115      " 

REFERENCES 

Liquid  Futfl.    B.  H.  Thwaite,  London,  1887.     (Spon.) 

Chemical  Technology.     Groves  and  Thorp.     Vol.  1,  Fuel,  by  Mills  and  Rowan, 

Phila.,  1889.     (Blakiston.) 
Feuerungsanlagen.    F.  Fischer,  Karlsruhe,  1889. 
Liquid  Fuel.     E.  A.  B.  Hodgetts,  London,  1890.     (Spon.) 
Die  Feuerung  mit  fliissigem  Brennmaterialien.     I.  Lew,  1890. 
Fuels.    H.  J.  Phillips,  London,  1891. 
Fuels.     C.  W.  Williams  and  D.  K.  Clark,  London,  1891. 
Taschenbuch  fur  Feuerungstechniker.     F.  Fischer,  Stuttgart,  1893.     (Enke. ) 
Contribution  a  Pe'tude  des  Combustibles.    P.  Mahler,  Paris,  1893. 
Die  chemische  Technologie  der  Brennstoffe.    F.  Fischer,  Braunschweig,  1896. 

(Vieweg.) 
A  Treatise  on  the  Manufacture  of  Coke  and  the  Saving  of  By-Products.    John 

Fulton,  Scranton,  Pa.,  1895. 

Mineral  Industry,  1895,  215,  W.  H.  Blauvelt.     (By-Product  Coke  Ovens.) 
Die  Chemie  der  Steinkohle.    F.  Muck,  Leipzig,  1891.     (W.  Engelmann.) 
Die  Gasfeuerungen  fur  Metallurgische  Zwecke.     A.  Ledebur,  Leipzig,  1891. 

(Felix.) 

Grundlagen  der  Koks-Chemie.    Oscar  Simmersbach,  Berlin,  1895.    (J.  Springer.) 
Gas  and  Fuel  Analysis  for  Engineers,  A.  H.  Gill,  New  York,  1896.     (Wiley 

&  Sons.) 

WATER 

The  industrially  important  sources  of  water  may  be  thus  sum- 
marized :  — 

1.  The  sea. 

2.  Eain  water. 

3.  Surface  waters,  consisting  of 

a.  Flowing  waters  (streams). 

b.  Still  waters  (ponds,  lakes,  etc.). 

4.  Ground  waters,  furnished  by 

a.  Springs. 

b.  Shallow  wells  (penetrating  but  one  geological  stratum). 

c.  Deep  wells  (passing  through  more  than  one   such 

stratum). 

*  Orton,  Geology  of  Ohio,  Vol.  VI.,  p.  644, 


WATER  35 

The  impurities  contained  in  water  depend  upon  the  character  of 
the  ground  with  which  it  has  been  in  contact ;  they  may  be  classed 
as  soluble  and  insoluble.  The  more  common  soluble  impurities  are 
calcium  chloride,  calcium  sulphate,  calcium  bicarbonate,  magnesium 
chloride,  magnesium  sulphate,  magnesium  bicarbonate,  sodium  chlo- 
ride, sodium  sulphate,  sodium  carbonate,  and  organic  matter.  The 
usual  insoluble  impurities  are  sand,  clay,  and  organic  matter.  In- 
soluble suspended  matter  can  be  removed  by  allowing  the  water  to 
stand  and  drawing  off  the  clear  portions  from  the  sediment,  or  by 
filtration  (p.  11).  If  the  water  contains  much  organic  matter,  a 
layer  of  coke  or  charcoal  dust  is  sometimes  put  in  when  building 
a  sand  filter.  A  water  may  contain  large  amounts  of  soluble  im- 
purities, and  yet  answer  very  well  for  washing  and  levigating,  while 
for  use  in  condensers  and  cooling  apparatus  this  scarcely  need  be 
considered  at  all.  Soluble  matter  may  be  injurious  for  some  pur- 
poses and  beneficial  for  others,  but  as  a  rule  water  carrying  much 
suspended  matter  must  be  purified. 

The  soluble  impurities  cause  the  most  difficulty  in  technical 
work,  especially  when  the  water  is  to  be  used  in  steam  boilers. 
According  to  the  nature  of  these  impurities,  water  is  hard,  soft, 
saline,  or  alkaline. 

Hard  water  contains  one  or  more  of  the  salts  of  calcium,  mag- 
nesium, iron,  or  aluminum  in  solution,  and  is  usually  defined  as  one 
which  precipitates  soap  from  solution.  Hence  it  is  customary  to 
determine  hardness  by  titration  with  a  standard  soap  solution. 
Temporary  hardness  is  caused  by  the  presence  of  the  bicarbonates  of 
calcium  or  magnesium,  while  permanent  hardness  is  principally  due 
to  the  neutral  chlorides  and  sulphates  of  these  metals.  The  neutral 
carbonates  of  calcium  and  magnesium  are  insoluble,  but  if  carbon 
dioxide  is  present  in  the  water,  they  dissolve,  probably  forming  the 
bicarbonates  CaH2(C03)2  and  MgH2(C03)2. 

Soft  waters  contain  very  little  mineral  matter.  Eain  water  as  it 
falls  is  very  soft,  and  if  it  could  be  collected  uncontaminated  would 
be  far  the  best  for  most  purposes.  Natural  soft  waters  usually  fall 
upon  ground  nearly  free  from  lime  or  magnesia,  and  collect  in 
streams  or  ponds  by  percolating  through  the  soil.  Very  often  the 
soil  contains  peat  or  other  decayed  vegetable  matter,  from  which  the 
water  may  derive  organic  impurities  or  coloring  substances,  which 
affect  its  use  for  many  purposes.  Peaty  waters  often  contain  organic 
acids  or  other  material  which  causes  them  to  attack  iron  or  lead. 

Saline  and  alkaline  waters  are  those  in  which  large  quantities  of 
soluble  sulphates,  chlorides,  or  carbonates  occur.  They  frequently 


36  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

contain  bromides  and  other  salts.  Sea-water  and  certain  mine  waters 
containing  sulphates  of  copper,  iron,  or  other  metals,  are  the  most 
important  of  the  saline  group.  Alkaline  waters,  e.g.  the  "  alkali " 
waters  of  the  western  states,  contain  considerable  quantities  of  the 
alkaline  carbonates  or  sulphates.  • 

The  purification  of  water  for  use  in  the  industrial  arts  often  pre- 
sents considerable  difficulty  owing  to  the  nature  of  the  impurity  or 
the  magnitude  of  the  plant  necessary  for  large  works.  When  pos- 
sible the  quality  of  the  water  should  be  considered  in  locating  the 
works,  so  that  little  or  no  purification  may  be  necessary.  However, 
in  most  localities  the  boiler  water  needs  some  treatment. 

The  following  are  the  usual  methods  of  removing  temporary 
hardness :  — 

1.  Treating  with  sodium  carbonate  or  sodium  hydroxide. 

CaH2(C08)2+  Na2C03  =  CaC03  +  2NaHC03; 
CaH2(C03)2  +  2  NaOH  =  CaC03  +  Na2C03  +  2  H20. 

2.  Treating  with  calcium  hydroxide  or  "  milk  of  lime." 

CaH,(C03)2  +  Ca(OH)2  =  2  CaC03  +  2  H20. 

If  possible,  it  is  best  to  use  only  the  clear  calcium  hydroxide  solution 
obtained  by  allowing  the  undissolved  lime  to  settle,  but  this  requires 
much  space  for  precipitating  and  settling  tanks.  If  the  "  milk  of 
lime  "  is  used,  the  proper  quantity  of  quicklime  is  carefully  weighed, 
slaked  in  a  small  amount  of  water,  and  the  "  milk  "  then  thoroughly 
mixed  with  the  water  to  be  purified.  This  is  Clark's  process.  The 
sludge  of  calcium  carbonate  is  best  removed  by  the  filter  press  (p.  12). 

3.  Treating  with  barium  hydroxide  or  with  sodium  oxalate. 

CaH2(C03)2  +  Ba(OH)2  =  CaC03  +  BaCO8  +  2  H2O ; 
CaH2(C03)2  +  Xa2C  A  =  CaC  A  +  2  NaHC03. 
These  are  very  effective,  but  are  too  expensive  for  most  purposes. 

4.  Heating  the  water  to  boiling,  either  in  the  open  air  or  in 
special  heaters.     This  decomposes  the  bicarbonates. 

CaH2(C03)2  =  CaC03  +  H20  +  C02. 

The  permanent  hardness  is  less  easily  remedied,  for  in  every 
case  treatment  of  the  water  leaves  some  substance  more  or  less 
deleterious  in  solution,  as  shown  in  the  following  reactions :  — 

1)  CaS04+  Na2C03  =  CaC03  +NaJ304; 

2)  CaS04  +  Ba(OH)2  =  BaSO4  +  Ca(OH)2 ; 

3)  CaS04  +    BaCl2    =  CaCl2  +  BaS04; 

4)  CaCl2  +  Na2C204  = 


WATER  37 

Magnesium  and  iron  salts  react  like  the  calcium  salts,  though  the 
iron  precipitates  as  hydroxide  when  sodium  carbonate  is  used. 

When  water  containing  soluble  impurities  is  evaporated  in  a 
boiler,  a  more  or  less  coherent  deposit  called  boiler  scale  forms  on 
the  plates  and  tubes.  This  is  chiefly  composed  of  carbonate  and 
sulphate  of  calcium,  while  in  some  cases  magnesium  hydroxide,  mag- 
nesium sulphate,  iron  hydroxide  or  oxide,  silica,  and  organic  matter 
are  present.  Calcium  carbonate  alone  forms  a  porous  and  non-adher- 
ent scale,  which  is  easily  removed  by  "blowing  off"  the  boiler. 
Calcium  sulphate  forms  a  hard,  compact  scale,  which  adheres  very 
firmly.  Scale  formation  is  detrimental  in  several  ways ;  since  it  is 
a  poor  conductor  of  heat,  the  fires  must  be  driven  harder;  it  sepa- 
rates the  water  from  the  boiler  plates,  which  are  thus  overheated 
and  rapidly  burned  out.  Moreover,  the  tubes  and  feed  pipes  become 
clogged,  and  their  efficiency  is  much  reduced. 

The  decomposition  of  bicarbonates  of  calcium  and  magnesium 
by  heat,  which  has  already  been  mentioned,  may  take  place  in  the 
boiler.  Then,  too,  calcium  sulphate  is  rendered  less  soluble  by  the 
high  temperature  and  pressure  within  the  boiler,  and  is  deposited  as 
scale.  If  the  water  carries  magnesium  sulphate,  this  deposits  as 
monohydrated  salt  (MgS04  •  H.,0).  Magnesium  chloride  is  very 
troublesome,  for  it  not  only  forms  a  scale,  but  also  attacks  the  iron 
of  the  boiler,  the  probable  decomposition  being  shown  in  the  follow- 
ing equation :  — 

MgCl2  +  Fe  +  2  H,0  =  Mg(OH)2  +  FeCL  +  H2. 

For  the  removal  of  "temporary  hardness,"  and  to  a  certain 
extent,  of  calcium  and  magnesium  sulphates  as  well,  "feed  water 
heaters"  are  advantageous.  The  water  is  heated  in  these,  and  the 
scale-forming  matter  deposited,  before  it  is  delivered  into  the  boiler. 

A  recent  suggestion  *  is  the  use  of  sodium  bichromate  within  the 
boiler,  as  a  precipitant  for  both  "temporary"  and  "permanent" 
hardness.  The  reactions  involved  are  the  following :  — 

CaH2(C03)2  +  Na2Cr207  =  CaCr04  +  Na2Cr04  +  2  C02  +  H20 ; 
CaS04  +  Na2Cr207  =  CaCrO4  +  Na2S04  +  Cr03 ; 
MgS04  +  Na2Cr207  =  MgCr04  +  Na2S04  +  Cr03. 

It  is  claimed  that  the  calcium  and  magnesium  chromates  precipi- 
tate in  the  boiler  as  a  loose,  non-adherent  mass,  which  is  removed  by 
"blowing  off"  daily.  It  is  further  claimed  that  the  free  chromic 
acid  does  not  attack  the  boiler  iron. 

*  Wyatt,  Eng.  Mining  Journal,  Vol.  LX.,  220. 


38  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

Much  care  is  necessary  to  avoid  an  excess  of  the  chemical  added. 
As  a  rule,  the  water  should  be  treated  before  it  goes  into  the  boiler, 
but  if  the  scale-forming  material  does  not  amount  to  more  than  ten 
grains  per  gallon,  the  purification  may  be  done  in  the  boiler  itself, 
followed  by  a  daily  "blowing  off."  A  good  circulation  of  water  in 
the  boiler  tends  to  keep  the  precipitated  material  loose  so  that  it 
may  be  easily  blown  out. 

Attempts  are  made  to  prevent  the  scale  from  attaching  itself  by 
introducing  oil  with  the  water.  Kerosene  is  said  to  be  the  best  for 
this  purpose ;  but  animal  or  vegetable  oils  may  be  decomposed  by 
the  heat  and  pressure  of  the  steam,  forming  glycerine  and  free  fatty 
acid.  This  acid  may  injure  the  boiler  or  the  pipes  and  valves  of 
the  pumps.  Mineral  oils  do  not  decompose  in  this  way,  but  may 
enter  into  the  scale  themselves. 

A  great  many  proprietary  "anti-scale"  preparations  are  sold, 
many  of  which  are  of  no  particular  value.  Most  of  them  are  to  be 
used  inside  the  boilers.  Some  are  supposed  to  act  chemically  on  the 
impurities,  and  others  are  mechanical,  preventing  the  adherence  of 
the  scale.  The  former  usually  contain  soda-ash,  caustic  soda, 
barium  hydroxide,  or  sodium  phosphate  or  sulphite.  Tannin,  usually 
in  the  form  of  sodium  tannate,  is  sometimes  employed,  by  which 
the  calcium  and  magnesium  are  separated  as  tannates. 

Saline  and  alkaline  waters  are  troublesome  in  a  boiler,  causing 
"priming,"  i.e.  the  passage  of  foam  and  water  through  the  steam 
chest  with  the  steam.  Sodium  carbonate  and  sulphate  are  particu- 
larly liable  to  induce  priming,  hence  an  excess  of  these  salts  must 
neither  be  added  nor  formed  in  the  process  of  purification.  One  of 
the  worst  complications  in  boiler  water  is  the  simultaneous  presence 
of  large  quantities  of  alkaline  chlorides  and  sulphates,  together 
with  magnesium  sulphate.  The  magnesium  sulphate  forms  a  bad 
scale,  and  yet  its  removal,  by  means  of  sodium  carbonate,  makes  the 
water  liable  to  prime.  This  difficulty  is  of  frequent  occurrence  in 
some  of  the  western  states,  and  no  satisfactory  method  of  treating 
such  waters  has  yet  been  proposed.  In  the  case  of  locomotives,  the 
usual  remedy  is  to  transfer  them  periodically  to  other  parts  of  the 
road,  where  a  soft  water  can  be  obtained,  which  will  dissolve  part  of 
the  scale,  and  thus  loosen  it  so  that  it  may  be  blown  out. 

In  regard  to  the  character  of  the  water  needed  for  the  various 
manufacturing  processes,  only  a  few  general  remarks  can  be  made 
here.  A  soft  water  is  desirable  for  a  soap  works  or  a  bleachery, 
since  the  insoluble  calcium  soaps  would  otherwise  be  precipitated 
and  cause  a  loss  of  soap,  or  injury  to  the  goods.  A  hard  water  will 


SULPHUR  39 

sometimes  cause  unevenness  in  the  shade  of  color  in  dyeing,  but  for 
some  dyes,  e.g.  Turkey  red  on  cotton,  it  is  beneficial.  Water  con- 
taining calcium  sulphate  is  considered  best  for  use  in  brewing. 
Hardness  of  the  water  is  of  little  consequence  to  the  paper  maker, 
but  suspended  matter  or  deep  color  is  bad.  Suspended  matter  or 
soluble  coloring  matter  is  also  injurious  for  a  bleachery,  a  dye  works, 
a  starch  factory,  or  in  fact  for  almost  any  industry  where  the  water 
conies  in  direct  contact  with  the  goods  or  product. 


REFERENCES 

A  Treatise  on  Steam  Boilers.     R.  Wilson,  London,  1875.     (Lockwood.) 

Die  Chemische  Technologic  des  Wassers.      F.  Fischer,  Braunschweig,  1880. 

(Vieweg.) 
Die  Verhiitung  und  Beseitigung  des  Kesselsteins.      W.  Storck,  Halle,  1881. 

(W.  Knapp.) 
A  Treatise  on  Steam  Boiler  Incrustations.     C.  T.  Davis,   Washington,  1884. 

(Industrial  Publishing  Co.) 
Water  Supply.     William  R.  Nichols,  1886. 
Report  on  Boiler  Waters  of  the  C.  B.  &  Q.  R.  R.    W.  L.  Brown,  Chicago,  1888. 

(H.  O.  Shepard  &  Co.) 
Die  Verunreinigung  der  Gewasser.      Dr.  K.  W.  Jurisch,  Berlin,  1890.     (R. 

Gartner.) 

Das  Wasser.     F.  Fischer,  Berlin,  1891.     (J.  Springer.) 
Das  Reinigen  von  Speisewasser  fur  Dampfkessel.    Dr.  A.  Rossel,  Winterthur, 

1891.     (Moritz  Kieschke.) 

L'Eau  dans  L'Industrie.     P.  Guichard,  Paris,  1894.     (Bailliere.) 
The  Purification  of  Boiler  Feed  Waters.     Dr.  F.  Wyatt.      (Eng.  Min.  Jour., 

1895,  220.) 

J.  Soc.  Chem.  Ind.,  1884,  51.    J.  H.  Porter. 
J.  Soc.  Chem.  Ind.,  1886,  267.    Macnab  and  Beckett. 
J.  Soc.  Chem.  Ind.,  1891,  611.    Archbutt  and  Deeley. 


SULPHUR 

Most  of  the  sulphur  used  in  the  industries  is  derived  from  the 
native  mineral,  which  is  found  in  many  places,  but  usually  in  vol- 
canic regions.  It  is  always  impure,  being  mixed  with  gypsum, 
aragonite,  clay,  or  other  matter,  in  the  interstices  of  which  the 
sulphur  is  deposited.  The  formation  of  sulphur  beds  may  have 
occurred  by  the  reaction  of  gases,  such  as  hydrogen  sulphide  and 
sulphur  dioxide,  with  each  other  or  with  oxygen ;  or  by  the  decom- 
position of  metallic  sulphides  through  the  agency  of  heat;  or  by 
the  reduction  of  sulphates,  especially  of  calcium  sulphate. 


40  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

The  first  is  probably  the  most  frequent  mode  of  deposition,  and 
may  be  observed  at  the  present  time  in  many  volcanic  districts 
where  hydrogen  sulphide  and  sulphur  dioxide  are  escaping.  The 
reactions  are  the  following:  — 

S02  +  2  H2S  =  2  H2O  +  3  S  ; 


These  gases  are  always  present  where  volcanic  action  is  in  progress. 

The  reduction  of  sulphates  has  probably  caused  the  formation 
of  some  stratified  deposits. 

By  far  the  largest  part  of  the  world's  supply  of  sulphur  comes 
from  Sicily,  but  some  is  obtained  in  Japan,  Italy,  Greece,  and  in 
the  United  States,  particularly  near  Humboldt,  Nevada,  at  Clear 
Lake,  California,  and  in  Louisiana.  But  the  price  of  the  foreign 
product  is  too  low  to  allow  profitable  working  of  the  deposits  in 
this  country. 

In  Sicily  it  is  disseminated  through  the  matrix,  sometimes  in 
considerable  masses  of  nearly  pure  sulphur,  but  usually  in  fine 
seams  or  grains.  The  methods  of  obtaining  it  are  very  crude  and 
wasteful.  The  mines  are  for  the  most  part  open  pits,  ranging  from 
200  to  500  feet  in  depth,  and  the  ore  is  carried  to  the  surface  in 
baskets  or  sacks  by  laborers,  who  ascend  by  inclined  paths  on  the 
walls  of  the  pit.  In  a  few  of  the  better  mines,  however,  hoisting 
machinery  is  now  used,  but  only  after  overcoming  the  determined 
opposition  of  the  laborers.  The  ore  is  generally  refined  in  a  very 
simple  manner,  the  process  being  carried  on  in  kilns  called  "  cal- 
ceroni."  As  usually  constructed,  these  are  shallow  pits,  about  30 
feet  in  diameter,  with  walls  about  10  feet  high,  made  tight  with 
mortar.  They  are  generally  built  on  a  hill-side,  and  the  sloping 
bottom  is  beaten  smooth.  The  ore  is  arranged  in  the  calcerone  so 
as  to  leave  a  few  vertical  draught  holes  from  top  to  bottom  of  the 
heap,  which  is  fired  by  dropping  burning  brush  or  straw  into  these 
openings.  The  sulphur,  forming  from  25  to  40  per  cent  of  the  ore, 
burns  freely  r  and  when  the  heap  is  well  on  fire,  the  draught  holes 
are  closed,  the  calcerone  covered  with  spent  ore,  and  the  whole  left 
for  several  days.  The  heat  given  out  by  the  burning  of  part  of  the 
sulphur  is  sufficient  to  melt  the  remainder  from  the  gangue,  and 
it  collects  in  a  pool  near  a  tap-hole,  made  in  the  wall  at  the  lowest 
point.  At  intervals  of  a  few  hours,  the  melted  sulphur  is  drawn 
off  into  moulds.  If  the  temperature  rises  above  180°  C.,  there  is 
a  large  formation  of  plastic  sulphur,  which  will  not  flow  from  the 


SULPHUR  41 

tap-hole.  The  time  necessary  to  burn  out  a  calcerone  varies  from  35 
to  80  days,  according  to  its  size,  the  weather,  and  the  nature  of  the 
impurities ;  e.g.  much  gypsum  retards  the  process  owing  to  the 
water  it  contains. 

Usually  from  a  quarter  to  a  third  of  the  sulphur  is  lost  as  sul- 
phur dioxide  during  the  burning.  As  this  causes  much  damage  to 
vegetation  in  the  vicinity,  the  burning  of  calceroni  is  prohibited 
during  the  spring  and  summer  months. 

It  has  been  proposed  to  separate  sulphur  by  heating  with  hot  air, 
with  steam  under  pressure  or  with  superheated  steam.  But  this 
is  unprofitable  on  account  of  cost  of  fuel  in  those  regions  where 
sulphur  occurs.  It  may  be  separated  by  a  solvent,  such  as  carbon 
disulphide,  which  may  be  recovered  afterwards,  but  this  necessitates 
an  expensive  plant.  But  treatment  with  a  solution  boiling  above 
the  melting  point  of  sulphur  has  proved  successful  for  some  ores. 
The  ore  is  placed  in  an  iron  basket  or  crate  and  suspended  in  a 
boiling  solution  of  calcium  chloride,*  which  boils  at  125°  C.  Since 
sulphur  fuses  at  115°  to  120°  C.,  it  melts  and  flows  away  from  the 
matrix  of  stones,  etc. ;  passing  through  the  basket  meshes,  it  falls  to 
the  bottom  of  the  tank,  and  is  drawn  off  and  cast  in  moulds.  After 
the  sulphur  is  melted  out,  the  basket  of  hot  stones  is  lowered  into 
a  tank  of  water,  which  is  thus  heated  by  the  hot  stones,  while  it 
removes  the  calcium  chloride  from  them.  This  warm  water  is  then 
used  to  replace  that  lost  by  evaporation  from  the  boiling  calcium 
chloride  solution.  This  process  causes  no  loss  of  sulphur  as  sulphur 
dioxide,  and  no  nuisance  is  created,  while  a  fairly  pure  product  is 
obtained.  The  calcium  chloride  used  is  a  waste  product  of  the 
ammonia  soda  industry. 

In  this  country,  extraction  with  superheated  steam  f  has  been 
tried  and  yields  an  excellent  quality  of  sulphur,  without  any  forma- 
tion of  sulphur  dioxide.  But  the  cost  of  fuel  in  the  West  is  an 
obstacle  to  further  development.  In  Louisiana,  it  is  proposed  to 
force  steam,  under  pressure,  through  driven  wells  or  tubes,  into  the 
sulphur  deposit.  The  sulphur,  having  been  liquefied  by  the  heat, 
is  forced  to  the  surface  by  the  steam  pressure,  through  a  small  pipe 
inside  of  the  steam  pipe.  The  industrial  success  of  the  process  is 
as  yet  somewhat  problematical. 

Iron  pyrites  (FeS2),  when  heated  in  a  closed  retort,  yields  one 
atom  of  sulphur  per  molecule  of  sulphide,  and  has  been  used  as 
a  source  of  sulphur,  but  the  process  is  not  now  employed. 

*  Vincent ;  Bull.  Soc.  Chim.,  40,  528.     Am.  Chem.  Jour.,  VI,  63. 
t  J.  Soc.  Chem.  Ind.,  1887,  439,  442;  1889,  696.. 


42 


OUTLINES  OF  INDUSTRIAL   CHEMISTRY 


A  small  portion  of  the  sulphur  of  commerce  is  that  known  as 
recovered  sulphur.  This  is  chiefly  obtained  from  the  calcium  sul- 
phide waste  of  the  Leblanc  soda  process  (p.  73),  although  a  small 
quantity  comes  from  the  residues  from  the  purification  of  illuminat- 
ing gas  by  means  of  moist  iron  oxide.  When  iron  oxide  is  used 
to  purify  gas,  the  following  reactions  take  place :  — 

Fe2O3  •  3H20  +  3H2S  =  2FeS  +  S  +  6  H20. 

On  exposure  to  the  air,  this  moist  ferrous  sulphide  is  oxidized 
thus :  — 

2  FeS  +  3  H20  +  3  O  =  Fe2O3  -  3  H.O  +  2  S. 

Hence  the  iron  oxide  is  "revivified"  and  may  be  used  again,  and 
on  exposure  to  the  air,  oxidation  of  more  ferrous  sulphide  takes 


FIG.  20. 

place  with  further  deposition  of  sulphur  in  the  mass.  After  repeat- 
ing this  operation  a  number  of  times,  there  is  sufficient  free  sulphur 
to  be  profitably  distilled  by  heating  in  a  retort.  But  the  quantity 
of  recovered  sulphur  is  very  small  in  comparison  with  the  total 
annual  demand,  and  there  seems  but  little  prospect  of  any  great 
advance  in  the  industry. 

With  the  exception  of  recovered  sulphur,  the  above  processes 
yield  a  crude  impure  product,  which,  however,  is  good  enough  for 
a  large  number  of  manufacturing  operations.  But  for  some  pur- 
poses a  further  purification  is  necessary.  This  is  generally  done 
by  distillation  in  a  cast-iron  retort,  or  in  Dejardin's  apparatus 
(Fig.  20).  The  crude  sulphur  is  melted  in  the  vessel  (C),  heated 
by  the  waste  heat  of  the  fire,  and  is  then  run  into  the  retort  (B), 


SULPHUR  43 

heated  directly  by  the  fire.  The  vapors  pass  into  the  receiving 
chamber  (E),  which  is  usually  made  of  brick.  If  the  temperature 
of  the  chamber  (E)  is  not  allowed  to  rise  above  110°  C.,  the  vapors 
condense  at  once  to  a  fine  powder,  which  is  sold  under  the  name 
of  "flowers  of  sulphur.'7  If  the  temperature  of  (E)  rises  much 
above  110°  C.,  the  vapors  condense  as  a  liquid,  which  is  drawn  off 
into  moulds,  forming  the  "roll  brimstone"  of  commerce. 

The  chief  uses  of  crude  sulphur  are :  for  making  sulphuric  acid ; 
as  a  germicide  in  combating  Phylloxera,  a  disease  of  the  grape  (this 
disposes  of  nearly  one  quarter  of  the  yearly  production);  and  in 
making  ultramarine  and  carbon  disulphide.  The  principal  uses  of 
refined  sulphur  are:  for  making  gunpowder  and  matches,  and  for 
vulcanizing  rubber. 

Sulphur  melts  at  115°-120°  C. ;  it  is  a  very  poor  conductor  of  heat 
and  electricity,  and  dissolves  easily  in  carbon  disulphide,  less  readily 
in  chloroform,  benzol,  turpentine,  and  other  oils.  Its  specific  gravity 
is  1.98-2.04. 

Sicily,  owing  to  its  favorable  situation  as  a  shipping  point,  the 
abundance  of  cheap  labor,  and  the  richness  of  its  deposits  will  prob- 
ably continue  to  supply  the  major  part  of  the  sulphur  consumed. 
But  Japanese  sulphur  has  become  a  considerable  competitor  with 
the  Sicilian,  and  a  deposit  recently  opened  in  one  of  the  New  Heb- 
rides islands  (Tanna)  gives  promise  of  future  importance. 

SULPHUR   DERIVATIVES 

The  most  important  sulphur  compound  is  sulphur  dioxide  (S02). 
This  is  extensively  made  for  the  manufacture  of  sulphuric  acid  by 
roasting  iron  pyrites  (p.  49).  Liquid  sulphur  dioxide  is  now  an 
article  of  trade,  but  the  gas  is  usually  made  where  it  is  to  be  used, 
by  burning  sulphur  with  a  proper  supply  of  air.  It  is  occasionally 
made  by  decomposing  sulphuric  acid  by  means  of  copper  or  char- 
coal :  — 

2  H2SO4  +  Cu  =  CuS04  +  2  H20  +  S02 ; 

2  H2S04  +  C  =  2  H20  +  C02  +  2  S02. 

Charcoal  yields  a  gas  which  is  not  pure,  but  may  be  used  for  some 
purposes.  Processes  for  the  recovery  of  sulphur  dioxide  from  furnace 
gases,  by  passing  them  through  towers  filled  with  coke,  over  which 
water  trickles,  have  been  proposed,  but  are  not  very  practicable. 

Sulphur  dioxide  is  used  in  making  sulphuric  acid ;  as  a  bleaching 
agent  for  wool,  hair,  straw,  and  other  tissues ;  as  a  disinfectant  and 
germicide;  for  use  in  ice  machines;  for  making  the  acid  sulphite 


44  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

liquor  used  in  manufacturing  wood  pulp;  for  the  preparation  of 
sodium  bisulphite ;  and  to  a  small  extent  in  the  leather  and  glucose 
industries. 

Substances  such  as  wool  and  straw,  when  bleached  by  exposure 
to  sulphur  dioxide  gas,  slowly  regain  their  original  color  on  exposure 
to  the  light.  The  coloring  matter  is  not  destroyed,  but  probably 
unites  with  the  sulphur  dioxide  to  form  a  colorless  compound,  which 
slowly  decomposes. 

Sodium  bisulphite  (NaHS03)  is  formed  by  saturating  sodium,  carbo- 
nate solution  with  sulphur  dioxide :  — 

Na^CO,  +  H2O  +  2  S02  =  2  NaHS03  +  C02. 

It  forms  a  strong  smelling  solution  used  as  an  "antichlor"  to 
remove  excess  of  chlorine  from  the  fibres  of  bleached  cotton  or  linen 
goods.  Its  reaction  is  probably  as  follows :  — 

Ca  (CIO),  +  2  NaHS03  =  2  NaCl  +  CaS04  +  H2S04 ;  or, 
=  Na2S04  +  CaS04  +  2  HC1 ; 

2  Cl  +  NaHS03  +  H20  =  NaCl  +  H2S04  +  HC1 ;  or, 
=  NaHS04  +  2  HC1. 

It  also  finds  some  use  in  other  industries,  such  as  chrome  tannage, 
brewing,  glucose,  and  starch  making.  The  solution  of  bisulphite 
decomposes  on  evaporation,  giving  off  part  of  the  sulphur  dioxide, 
and  forming  neutral  sulphite  of  sodium. 

Calcium  bisulphite  [CaH2(S03)2]  is  made  by  passing  sulphur  di- 
oxide into  milk  of  lime.  It  is  probably  a  solution  of  neutral  sulphite 
in  an  excess  of  aqueous  sulphurous  acid.  It  is  used  in  much  the 
same  way  as  the  sodium  salt. 

Hyposulphurous  acid  (H2S02)  and  hyposulphite  of  sodium  are  of 
some  importance  as  powerful  bleaching  and  reducing  agents.  The 
acid  is  formed  in  solution  by  the  action  of  iron  or  zinc  on  aqueous 
sulphurous  acid :  — 

H2S03  +  Zn  =  ZnO  +  H2S02. 

The  zinc  oxide  then  combines  with  another  molecule  of  sulphurous 
acid,  to  form  zinc  sulphite  and  water. 

Sodium  hyposulphite  (NaHS02)  is  made  when  zinc  is  dissolved  in 
sodium  bisulphite :  — 

3  NaHS08  +  Zn  =  Na2Zn  (S03)2  +  H20  +  NaHS02. 

The  zinc-sodium  sulphite  crystallizes,  leaving  the  sodium  hyposul- 
phite in  solution.  The  latter  salt  is  very  unstable,  rapidly  absorbing 


SULPHURIC  ACID  45 

oxygen  from  the  air,  and  should  be  made  immediately  before  needed. 
It  is  much  used  for  reducing  indigo  in  the  so-called  "  hydrosulphite 
vat."  It  is  to  be  noted  here  that  the  salt  sold  in  commerce  under 
the  name  of  "  hyposulphite  of  sodium  "  is  properly  the  thiosulphate 
(  Xa2S203  •  5  H20).  This  is  made  by  digesting  sulphur  with  a  solution 
of  neutral  sodium  sulphite  or  sodium  hydroxide  :  — 


6  NaOH  +  4  S  =  Na2S2O3  +  2  Na^S  +  3  H20. 

Sodium  thiosulphate  is  also  obtained  from  the  waste  sulphide  liquors 
of  the  Leblanc  soda  process  (p.  83).  It  crystallizes  with  five  mole- 
cules of  crystal  water,  ISra2S203  •  5  H2O,  and  is  largely  used  in  chrome 
tanning,  in  paper  bleaching,  and  in  photography. 

REFERENCES 

Sulphuric  Acid  and  Alkali,  Vol.  1,  2d  Ed.     G.  Lunge,  London,  1889. 

Mineral  Resources  of  the  United  States.     (1882-1893.) 

United  States  Consular  Reports  of  the  Sulphur  Industry. 

Mineral  Industry,  Vols.  1-5.     (1892-1896.) 

Journal  Society  Chemical  Industry,  1882,  97. 

Journal  Analytical  and  Applied  Chemistry,  1892,  690.     (K.  F.  Stahl.) 

SULPHURIC  ACID 

Sulphuric  acid  is  probably  the  most  important  of  all  chemicals, 
because  of  its  extensive  use  in  a  very  large  number  of  manufactur- 
ing operations.  Of  the  immense  quantities  made  yearly,  the  greater 
part  does  not  come  upon  the  market  ;  for,  being  expensive  and  diffi- 
cult to  ship,  consumers  of  large  amounts  generally  make  their  own 
acid. 

The  commercial  grades  of  acid  have  special  names.  A  moder- 
ately strong  acid  (50°-55°  Be.),  such  as  condenses  in  the  lead  cham- 
bers, is  known  as  "chamber  acid.7'  It  contains  from  62  to  70  per 
cent  of  H2S04,  and  is  strong  enough  for  use  in  the  manufacture  of 
fertilizer,  and  for  other  purposes  requiring  a  dilute  acid.  By  con- 
centrating this  chamber  acid,  an  acid  of  60°  Be.  is  obtained,  contain- 
ing about  78  per  cent  of  H2S04,  which  is  siifficiently  strong  for  most 
technical  uses.  Further  evaporation  in  platinum  or  iron  pans  yields 
an  acid  of  66°  Be.,  containing  93.5  per  cent  of  H2S04,  and  known  as 
oil  of  vitriol.  Faming  or  Nordhausen  acid,  which  is  still  more  con- 
centrated, is  prepared  by  special  means.  It  is  essentially  a  solution 
of  sulphuric  anhydride  (S08)  in  sulphuric  acid.  This  is  the  acid 
which  was  prepared  by  the  alchemists  in  the  Middle  Ages. 


46  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

In  about  the  year  1740,  Ward,  an  Englishman,  began  to  make 
sulphuric  acid  on  a  moderately  large  scale.  He  burned  sulphur  and 
nitre  (KN03)  together,  and  condensed  the  vapors  in  glass  vessels 
containing  a  little  water.  The  dilute  acid  so  formed  was  then  con- 
centrated in  glass  alembics  or  retorts.  In  this  way  an  acid  was 
produced  at  a  lower  price  than  the  fuming  acid  could  be  made, 
and  the  industry  was  soon  established  011  a  commercial  scale.  The 
reactions  involved  in  Ward's  process  are  the  bases  of  the  method 
now  in  use ;  this  consists  in  bringing  together,  under  suitable  condi- 
tions, sulphur  dioxide,  oxygen,  and  water  as  steam,  in  the  presence 
of  certain  oxides  of  nitrogen.  The  latter  probably  act  as  carriers 
of  the  oxygen,  causing  it  to  unite  with  the  sulphur  dioxide  and 
water  to  form  the  acid.  The  apparent  reaction  is :  — 

S02  +  HaO  +  0  =  H2S04. 

But  this  does  not  represent  the  actual  process,  which  is  more 
complicated  than  it  at  first  appears.  Several  theories  have  been 
advanced  to  explain  the  reactions  occurring  in  the  lead  chambers, 
and  the  part  taken  by  the  nitrogen  oxides,  but  the  most  generally 
accepted  one,  that  of  Lunge,  regards  nitrous  anhydride  (N203)  *  as 
the  essential  f actor. f  According  to  this  view,  the  principal  reac- 
tions involved  are  as  follows  :  — 

1)  2  S02  +  N203  +  O2  +  H20  =  2  S02  •  (OH)  .  (ONO)  (Nitrosylsul- 
phuric  acid) ; 

2)  2  S02  -  (OH)  •  (ONO)  -f  H20  =  2  S02(OH)2  +  N203 ;  or, 

3)  2  S02(OH)(ONO)  +  S02  +  0  +  H20  =  3  S02(OH)2  +  N2O3. 

First  there  is  a  union  of  sulphur  dioxide,  nitrous  anhydride, 
oxygen,  and  water,  to  form  nitrosylsulphuric  acid,  which  probably 
separates  as  part  of  the  mist  or  fog  seen  in  the  lead  chambers.  But 
in  the  presence  of  water  vapor  or  of  dilute  sulphuric  acid,  this 
nitrosylsulphuric  acid  is  at  once  decomposed,  according  to  reac- 
tion (2),  sulphuric  acid  being  formed,  and  nitrous  anhydride  regen- 
erated; or  if  sulphur  dioxide  and  oxygen  are  concerned  in  the 
process,  then  reaction  (3)  occurs.  This  cycle  of  reactions  repeats 
an  indefinite  number  of  times.  But  in  the  first  lead  chamber,  where 
the  temperature  is  rather  high  and  an  excess  of  water  vapor  is 

*  Ramsey  and  Cundall  (J.  Chem.  Soc.,  1885,  672)  maintain  that  N2O3  exists  only 
as  a  liquid,  and  on  heating,  it  decomposes  into  NO  and  NO2 ;  accepting  this  view, 
N2O3  as  such,  cannot  be  present  in  the  lead  chambers,  where  the  temperature  is 
over  60°  C. 

t  Hurter  (J.  Soc.  Chem.  Ind.,  1882,  49  and  83)  supports  the  theory  that  nitrogen 
peroxide  (NO2)  plays  an  important  part  in  the  process. 


SULPHURIC   ACID  47 

usually  present,  the  following  secondary  reactions  probably  occur 
to  a  greater  or  less  extent  :  — 

4)  2  S02  •  (OH)  •  (ONO)  +  S02  +  2  H20  =  3  H2S04  +  2  NO, 

this  reaction  being  only  momentary. 

Since  there  is  usually  an  excess  of  oxygen  present,  however,  the 
nitric  oxide  here  formed  is  at  once  brought  into  action  again,  thus  :  — 

5)  2  S02  +  2NO  +  3  0  +  H20  =  2  S02-  (OH)  .  (ONO). 

If  there  is  a  deficiency  of  oxygen,  the  nitric  oxide  is  not  returned 
to  the  process,  but  passes  through  the  several  chambers  and,  since 
it  is  not  absorbed  by  the  concentrated  acid  in  the  Gay-Lussac  tower, 
it  escapes  into  the  atmosphere  and  is  lost. 

The  nitrogen  oxides  are  derived  from  nitric  acid,  or  by  the  action 
of  sulphuric  acid  on  sodium  nitrate  in  the  nitre  pots.  When  nitric 
acid  is  used,  it  must  be  introduced  in  the  form  of  vapor,  or  at  least 
as  a  very  fine  spray,  whereupon  it  reacts  as  follows  :  — 


6)   2S02-f2HN03 
Perhaps  this  reaction  really  occurs  in  two  stages,  thus  :  — 

(a)  S02  +  HN03  =  S02  -  (OH)  .  (ONO)  ; 

(b)  2  S02  •  (OH)  •  (ONO)  +  H20  =  2  H2S04  +  N203. 

The  formula  assigned  to  the  nitrosylsulphuric  acid  may  perhaps 

/m 

be  written  S02<         ,  and  the  compound  would  then  be  called  nitro- 
\ 


sulphonic  acid.  But  in  either  case  the  existence  of  the  substance  is 
only  transitory,  it  being  broken  up  at  once  by  the  steam  and  sulphur 
dioxide  present  when  the  process  is  working  properly.  In  case  there 
is  a  deficiency  of  water  vapor  in  the  chambers,  and  especially  if  the 
temperature  falls  too  low,  the  nitrosylsulphuric  acid  may  separate 
as  crystals,  which  deposit  at  various  points  on  the  walls,  forming 
"chamber  crystals."  This  is  an  undesirable  accident,  for  when 
steam  or  water  come  in  contact  with  them  they  decompose  into  sul- 
phuric acid,  nitric  acid,  and  nitrogen  peroxide  (N204)  :  — 

4  S02  •  (OH)  •  (ONO)  +  2  H20  =  4  H2S04  +  N204  +  2  NO. 
Then  the  nitrogen  peroxide  unites  with  some  of  the  water, 
N204  +  H2O  =  HN02  +  HN03, 

forming  nitrous  and  nitric  acids  directly  on  the  walls,  corroding  the 
lead  at  the  point  where  the  cluster  of  crystals  was  attached.  To 


48  OUTLINES  OF  INDUSTRIAL   CHEMISTRY 

prevent  this  separation  of  "  chamber  crystals  "  and  the  retention  of 
nitrogen  oxides  in  the  sulphuric  acid  an  excess  of  steam  in  the  lead 
chambers  is  preferred,  although  it  dilutes  the  acid  somewhat. 
The  raw  materials  employed  in  sulphuric  acid  making  are :  — 

1.  Sulphur. 

(a)   Crude  brimstone. 

(6)   Metallic  sulphides,  such  as  iron  pyrites,  chalcopyrite 

(copper  pyrites),  sphalerite  (zinc  blende),  etc. 
(c)    Hydrogen  sulphide  (seldom  used). 

2.  Sodium  nitrate  or  nitric  acid. 

3.  Water  as  steam. 

4.  Oxygen  as  air. 

The  acid  may  be  made  from  brimstone,  pyrites,  blende,  or  hydro- 
gen sulphide,  but  they  are  not  used  together. 

Since  the  burners  and  chambers  employed  for  one  source  of  sul- 
phur cannot  be  adapted  to  that  of  another  without  extensive  altera- 
tions, the  manufacturer  must  decide  what  material  he  will  use,  and 
erect  his  plant  accordingly.  Crude  sulphur  from  the  calceroni  gives 
a  very  pure  acid  free  from  arsenic,  iron,  copper,  or  zinc,  and  much 
smaller  condensing  chambers  may  be  used  for  a  given  yield  than 
when  pyrites  or  blende  is  employed.  The  sulphur  is  placed  in  iron 
retorts  or  on  trays  in  brick  ovens,  and  ignited.  The  combustion  is 
easily  controlled  by  regulating  the  amount  of  air  admitted  to  the 
retort.  Usually  the  hot  vapors  from  the  brimstone  burners  are 
passed  through  a  narrow  flue  or  passage,  into  which  a  regulated 
supply  of  air  is  admitted.  This  insures  complete  combustion  of  any 
sulphur  that  may  distil  owing  to  too  great  heat  in  the  retort.  To 
prevent  clogging  and  loss,  as  much  of  the  sulphur  as  possible  is  con- 
verted to  dioxide. 

Pyrites,  or  natural  disulphide  of  iron  (FeS2),  is  a  dense,  hard 
mineral  of  crystalline  structure  and  pale  yellow  color.  The  largest 
deposits  in  the  United  States  are  in  Virginia,  at  Mineral  City,  and 
at  Charlemont  in  Massachusetts.  Of  the  foreign  deposits,  those  in 
Spain  *  are  the  most  important.  A  pure  pyrites  contains  53.3  per 
cent  of  sulphur,  but  that  commonly  used  for  acid  making  carries 
from  43  to  48  per  cent.  It  seldom  pays  to  use  an  ore  with  less  than 
35  per  cent  of  sulphur,  for  it  will  not  support  its  own  combustion. 

The  first  proposal  to  use  pyrites  originated  with  an  Englishman 
named  Hill,  who  took  out  a  patent  for  the  process  in  1818.  But  it 
was  not  until  1838,  when  the  Sicilian  government  sold  the  monopoly 

*  Spanish  pyrites  containing  copper  is  much  used  in  England  and  to  some  extent 
in  this  country,  the  burned  cinder  being  afterwards  treated  to  recover  the  copper. 


SULPHURIC   ACID  49 

of  the  sulphur  export  to  a  French  firm  which  nearly  trebled  the 
price  of  crude  brimstone,  that  pyrites  began  to  find  favor  with 
acid  makers.  At  the  present  time,  because  it  is  cheap  and  easily 
obtained,  pyrites  has  almost  completely  replaced  sulphur  for  acid 
making.  The  product  from  pyrites  is  usually  contaminated  with 
arsenic,  and  often  with  zinc,  copper,  and  selenium. 

By  the  oxidation  of  pyrites  in  a  suitable  furnace,  the  sulphur 
is  converted  to  dioxide,  and  iron  oxide  remains.  The  reaction  may 
be  written  as  follows :  — 

2  FeS2  +  11 0  =  4  S02  +  Fe2O3. 

This  is  not  exact,  however,  as  some  sulphur  remains  in  the  ore 
and  some  sulphur  trioxide  is  formed.  The  proper  regulation  of  the 
pyrites  burners  is  one  of  the  problems  of  the  manufacturer.  If  the 
ore  contains  over  35  per  cent  of  sulphur,  the  burning,  once  started, 
generates  sufficient  heat  to  maintain  the  combustion,  and  no  fuel 
is  necessary.  But  zinc  sulphide  and  the  "  mattes  "  from  metallurgi- 
cal processes  must  be  heated  by  fuel. 

The  complete  burning  of  pyrites  is  difficult.  With  lump  ore 
there  is  apt  to  be  a  kernel  in  the  centre  of  the  lump,  from  which 
the  sulphur  is  not  burned  out.  If  the  temperature  rises  too  high, 
the  charge  fuses  together,  forming  clinkers  or  "scar,"  and  chok- 
ing the  furnace.  If  too  much  air  is  admitted,  the  furnace  cools 
below  the  temperature  at  which  fresh  pyrites  will  ignite,  and  the 
gases  leaving  the  burner  are  so  diluted  that  the  desired  reactions  do 
not  take  place  in  the  lead  chambers.  With  "  smalls  "  the  tendency 
to  fuse  is  more  marked  than  with  lump  ore,  and  the  fine  ore  packs 
together  so  densely  that  the  air  will  not  penetrate  it,  and  unless  it 
is  constantly  stirred  only  the  surface  is  burned.  (The  lump  ore  is 
that  which  has  been  broken  to  about  the  size  of  a  goose  egg,  the 
"smalls"  constituting  what  will  pass  through  a  half-inch  screen.) 

Pyrites  burners  are  usually  built  in  benches  containing  from  three 
to  thirty  furnaces,  in  order  that  the  supply  of  gas  may  not  be 
broken,  while  charging  or  cleaning  one  furnace. 

A  burner  for  lump  ore  (Fig.  21)  *  consists  of  a  brick  furnace,  con- 
taining  a  grate  formed  of  single  loose  iron  bars  (B,  B)  having  a 
square  section,  and  resting  in  grooves  at  each  end.  These  bars  may 
be  turned  parallel  with  their  longitudinal  axes,  but  have  no  lateral 
motion.  They  are  so  adjusted  that  their  sides  are  at  an  angle  of 
45°  to  the  vertical.  After  a  charge  is  burned,  the  bars  are  given 
several  quarter  turns  by  means  of  a  key,  to  allow  the  cinders  on 
*  After  Ost,  Lehrbuch  der  technischen  Chemie. 


50 


OUTLINES  OF   INDUSTRIAL   CHEMISTRY 


them  to  drop  through  into  the  ash  pit.  Air  is  admitted  by  dampers 
beneath  the  grate.  When  properly  working,  the  cinders  resting  on 
the  bars  are  nearly  cold,  the  hottest  part  of  the  fire  being  eighteen 
inches  above  the  grate.  The  furnaces  are  lined  with  fire-brick, 
and  to  prevent  any  access  of  air  except  through  the  dampers,  the 
doors  (D,  D)  for  charging,  cleaning,  raking,  etc.,  are  make  to  fit 
closely,  and  are  generally  luted  with  clay. 

All  the  burners  in  one  bench  deliver  their  sulphur  dioxide  gas 
into  a  common,  wide  flue,  or  "dust  box"  (F),  where  any  fine  dust 
carried  along  by  the  gases  may  settle  before  they  enter  the  Glover 
tower.  This  dust  consists  of  unburned  pyrites,  arsenic,  antimony  or 
zinc  oxides,  iron  oxide,  etc. 

In  one  or  more  of  the  burners  a  cast-iron  "nitre  pot"  (P)  may  be 
set,  in  which  nitrous  gases  are  generated  by  the  action  of  sulphuric 


FIG.  21. 

acid  on  sodium  nitrate.  Or  the  pots  may  be  placed  in  a  small 
chamber  built  into  the  flue  (F),  and  heated  by  the  waste  heat  of 
the  burners.  Sometimes,  however,  the  pots  are  placed  in  separate 
furnaces. 

A  lump  burner  of  average  size  has  a  grate  area  of  15  to  25  square 
feet.  The  furnace  is  sometimes  made  slightly  hopper-shaped  in- 
side, so  that  it  is  larger  at  the  level  of  the  charging  doors  than  at 
the  grate  bars.  About  40  pounds  of  pyrites,  containing  48  per  cent 
of  sulphur,  are  burned  per  square  foot  of  grate  area  in  24  hours,  a 
larger  quantity  of  such  high-grade  ore  being  liable  to  cause  fusion, 
unless  great  care  is  exercised.  A  larger  quantity  of  poorer  ore  may 
be  burned  daily,  without  danger  of  fusion. 

A  number  of  burners  for  smalls  have  been  invented,  but  that 
most  commonly  used  is  the  Maletra  burner  (Fig.  22).  This  consists 
of  a  series  of  shelves,  about  5  by  8  feet  in  size,  arranged  in  a  tall 
furnace.  At  the  top  is  a  hopper,  through  which  the  smalls  are 
introduced,  falling  on  the  top  shelf,  on  which  they  are  spread  out  by 
rakes,  introduced  through  the  door  (A).  At  the  front  of  the  shelf 
is  an  opening  (B),  through  which  they  can  be  made  to  fall  upon  the 


SULPHURIC  ACID 


51 


next  shelf,  where  they  are  again  spread  out  in  a  thin  layer.  After 
a  time  they  are  raked  down  to  the  next  shelf,  and  so  on,  each  shelf 
being  hotter  than  the  one  preceding.  Finally,  the  spent  cinders  are 
raked  out  at  the  bottom  at  (C).  For  starting  the  furnace,  the  shelves 
are  heated  by  a  coal  fire  on  a 
special  grate,  but  after  the  temper- 
ature is  sufficiently  high  to  ignite 
the  charge,  combustion  continues 
from  the  heat  given  out  by  the 
burning  pyrites,  provided  the  fur- 
nace is  properly  regulated  and 
raked,  and  fresh  ore  is  introduced 
as  needed. 

Another  form  of  smalls  burner 
is  Spence's  furnace,  in  which  the 
fine  pyrites  is  put  into  a  long 
muffle,  heated  by  a  coal  fire  or  by 
the  waste  heat  from  lump  burn- 
Furnaces  modelled  after  the 


ers. 


FIG.  22. 


Spence  type  are  much  used  for 
roasting  zinc  blende  and  copper  mattes,  in  which  the  per  cent  of 
sulphur  is  too  low  to  support  combustion  without  external  heat. 
Even  from  poor  ore,  muffle  furnaces  yield  a  fairly  concentrated 
sulphur  dioxide  gas. 

The  Perret-Ollivier  furnace  is  a  shelf  burner,  in  which  the  shelves 
are  set  above  the  grate  of  an  ordinary  lump  burner.  The  smalls 
are  spread  upon  the  shelves  and  the  hot  gases  from  the  lump  ore 
pass  over  the  surface  of  the  fines,  heating  the  latter  to  the  combus- 
tion point. 

The  several  shelf  burners  above  described  must  be  raked  at  inter- 
vals, and  this  is  very  hard  labor  if  done  by  hand  rakes,  besides  allow- 
ing the  entrance  of  an  undue  amount  of  air.  To  remedy  these  defects, 
mechanical  raking  apparatus  has  been  applied,  some  being  very  suc- 
cessful, though  expensive  to  build  and  keep  in  repair. 

The  Gerstenhbf er  furnace  (Fig.  23)  is  used  somewhat  in  Germany. 
It  consists  of  a  tall  tower  containing  a  series  of  grates  made  of 
triangular  bars  (T,  T)  of  fire-clay  set  horizontally.  The  smalls  are 
introduced  from  a  hopper  (H)  at  the  top,  in  a  regular  stream,  and 
falling  from  one  grate  to  the  next,  are  exposed  to  the  hot  fumes  from 
the  burning  pyrites  on  the  lower  grates.  The  cinders  are  raked  out 
at  the  bottom  of  the  tower.  These  furnaces  are  about  17  feet  high 
and  4  by  2  feet  inside  diameter.  Before  starting,  the  burner  is  heated 


52 


OUTLINES  OF  INDUSTRIAL   CHEMISTRY 


FIG.  23. 


to  a  white  heat  by  a  coal  fire  on  the 
grate  (G),  but  no  more  fuel  is  used 
after  the  pyrites  is  once  ignited.  A 
proper  regulation  of  the  flow  of 
smalls  will  maintain  the  requisite 
temperature. 

The  Hasenclever-Helbig-  burner 
consists  of  a  lump  burner,  joined  to 
a  smalls  furnace,  which  is  a  tower 
containing  shelves,  set  at  an  incline 
of  38°,  the  alternate  shelves  being 
parallel.  The  smalls,  fed  in  at  the 
top  through  a  hopper,  fall  on  the  first 
shelf,  and  then  slide  down  from  one 
shelf  to  the  next.  At  alternate  ends 
of  the  shelves  are  openings  for  the 
fumes  to  pass  upwards.  The  hot 
gases  are  thus  forced  to  travel  back 
and  forth,  under  and  over  each  shelf, 
as  they  ascend  the  tower.  The  rate  of  the  flow  of  the  smalls  through 
the  burners  is  regulated  by  the  rapidity  of  the  discharge  of  cinders 
through  an  automatic  discharging  wheel  at  the  bottom. 

The  Glover  tower  is  placed  next  to  the  burners,  and  is  now  used 
in  nearly  all  sulphuric  acid  works.  Its  functions  are  to  set  free  the 
/nitrogen  oxides  from  the  Gay-Lussac  tower  acid  ;  to  cool  the  burner 
gases  to  a  temperature  of  from  50°  to  60°  C.  before  they  enter  the  lead 
chambers ;  to  furnish  a  large  part  of  the  steam  necessary  in  the  lead 
chambers ;  and  in  many  works  to  concentrate  the  dilute  acid  from 
the  lead  chambers  to  a  density  of  1.75  specific  gravity.  Moreover, 
it  doubtless  increases  the  yield  of  sulphuric  acid  from  a  plant  of 
given  lead  chamber  capacity,  for  some  acid  is  formed  directly  in 
the  tower  itself  in  addition  to  that  condensed  in  the  lead  chambers. 
The  tower  (20  to  30  feet  high  and  about  10  feet  across)  is  made  of 
sheet  lead,  joined  as  described  on  p.  53,  and  supported  on  a  frame- 
work of  timbers  or  steel.  It  is  lined  with  acid-resisting  brick  or  tile, 
laid  without  mortar,*  and  is  filled  with  broken  quartz  lumps  or  flint 
stones.  At  the  top  is  an  apparatus  for  distributing  the  acid,  which 
is  to  run  down  through  the  tower,  t  The  burner  gases  enter  at  the 
bottom,  and  pass  up  and  out  at  the  top,  through  a  pipe  leading  to 
the  lead  chambers.  These  form  the  most  important  part  of  a  sul- 


*  It  has  been  proposed  to  lay  the  brick  in  plastic  sulphur  as  a  cementing  substance, 
t  The  working  of  the  Glover  tower  is  described  in  connection  with  the  Gay-Lussac  tower. 


SULPHURIC   ACID.  53 

phuric  acid  plant,  and  it  is  in  them  that  the  reactions  involved  in 
the  formation  of  the  acid  take  place.  They  are  immense  boxes, 
made  by  joining  sheets  of  lead,  and  are  supported  from  a  strong 
timber  framework,  by  means  of  lugs  or  strips  of  lead,  attached  to 
the  outside  of  the  sheets.  The  joints  cannot  be  made  with  solder, 
but  the  edges  of  the  sheets  are  fused  together  by  means  of  an  aero- 
hydrogen  flame,  and  the  process,  called  "  lead  burning  "  is  both  diffi- 
cult and  slow.  At  several  points,  steam  may  be  introduced  into  the 
chambers  to  supply  water  vapor  as  needed.  Each  chamber  is  sus- 
pended above  a  large,  flat,  lead  pan  in  such  a  way  that  the  acid 
collecting  in  the  pan  forms  a  hydraulic  seal  for  the  lower  edge  of 
the  lead  chamber.  These  pans  are  6  or  8  inches  wider  than  the 
chamber,  and  have  sides  from  14  to  24  inches  high.  There  is  much 
difference  of  opinion  among  acid  makers  as  to  the  best  size  and 
number  of  the  lead  chambers.  There  are  usually  from  3  to  5,  with 
a  capacity  of  140,000  to  200,000  cubic  feet  in  the  system.  As  a 
rule,  the  first  chamber  is  the  largest,  and  in  it  the  greater  part  of 
the  acid  is  formed.  The  individual  chambers  vary  from  10,000  to 
80,000  cubic  feet  (100  by  40  by  20  feet).  In  this  climate  they  are 
enclosed  in  a  building  to  avoid  changes  of  temperature,  which  should 
not  vary  much  from  50°  to  65°  C.  in  the  first  chamber,  and  15°  above 
that  of  the  outside  air  in  the  last;  and  they  are  usually  on  the 
second  floor,  so  that  the  acid  may  flow  from  them  by  gravity  to  the 
evaporating  pans  sometimes  placed  on  top  of  the  pyrites  burners ; 
and  also  that  the  bottoms  may  be  better  watched  for  leaks.  In  order 
to  observe  the  working  of  each  chamber,  small  lead  dishes  are 
fastened  at  various  points  on  the  inside  of  the  chamber  wall,  and 
from  these,  pipes  called  "  drips  "  lead  to  test  glasses  outside,  where 
the  density  of  the  acid  may  be  taken.  A  better  method  is  to  place 
the  dish  inside  the  chamber  at  a  distance  from  the  wall,  support- 
ing it  aboye  the  level  of  the  condensed  acid,  and  connecting  it  by 
means  of  a  pipe  with  a  test  glass  outside.  Panes  of  glass  are  some- 
times set  at  opposite  points  in  the  chamber  walls,  so  that  the  color 
of  the  gases  may  be  observed.  This  is  quite  important  as  a  means 
of  controlling  the  process.  In  the  first  chamber  the  color  is  white 
and  opaque,  owing  to  the  copious  condensation  of  acid  vapor,  but 
in  the  succeeding  chambers  the  color  becomes  more  and  more  red- 
dish, owing  to  the  excess  of  nitrogen  oxides.  If  the  color  becomes 
pale  in  the  last  chamber,  there  may  be  a  deficiency  of  nitrous  vapors ; 
or  too  much  or  too  little  steam  ;  *  or  the  draught  may  not  be  properly 

*  The  steam  is  derived  from  a  boiler,  or  from  the  evaporation  of  water  from  the 
diluted  tower  acid  in  the  Glover  tower. 


54  OUTLINES  OF   INDUSTRIAL  CHEMISTRY 

regulated,  causing  too  much  or  too  little  oxygen  to  enter  the  cham- 
ber. The  standard  remedy  is  to  use,  at  once,  more  sodium  nitrate 
in  the  nitre  pots,  and  then  to  locate  the  difficulty  and  gradually 
bring  the  system  to  its  normal  working  condition. 

From  the  last  lead  chamber  the  gases  pass  to  the  Gay-Lussac 
tower,  whose  purpose  is  to  recover  the  oxides  of  nitrogen  which 
would  otherwise  be  lost.  The  tower  is  usually  about  50  feet  high, 
and  8  feet  across.  It  is  built  of  lead,  supported  on  a  timber  frame, 
in  much  the  same  way  as  the  Glover  tower.  (In  many  small 
modern  plants,  earthenware  pipe  of  large  diameter  [2  or  3  feet]  is 
often  used  instead  of  lead.)  The  tower  is  filled  with  metallurgical 
coke,  the  hardest  and  strongest  kind.  At  the  top  is  a  distributing 
apparatus  to  spread  the  acid  evenly  over  the  coke.  Sometimes  two 
towers  are  used,  the  gases  passing  up  through  one  and  then  to  the 
bottom  of  the  other,  and  up  through  this  to  the  chimney.  The  acid 
which  flows  down  the  Gay-Lussac  tower  is  that  which  has  been  con- 
centrated in  the  Glover  tower  to  a  density  of  from  150°  to  155°  Tw. 
(about  1.750  sp.  gr.).  Acid  of  this  strength  absorbs  the  nitrous 
anhydride  (N203)  and  the  nitrogen  tetroxide  (N02  or  N204),  but  does 
not  absorb  nitric  oxide  (NO)  or  nitrous  oxide  (N20).  Hence,  with 
normal  working  of  the  process,  only  that  part  of  the  nitrogen  oxides  is 
lost  which  is  reduced  to  nitrous  and  nitric  oxide.  If  there  is  an  excess 
of  oxygen  present,  some  of  the  nitric  oxide  is  converted  to  nitrous 
anhydride,  and  thus  saved.  The  absorption  of  these  nitrogen  oxides 
takes  place  only  when  concentrated  acid  is  run  through  the  Gay- 
Lussac  tower;  if  the  acid  is  of  less  than  1.50  sp.  gr.,  it  will  not 
absorb  them ;  for  best  results  it  should  be  1.75  sp.  gr.  The  solution 
of  nitrous  gases,  in  concentrated  sulphuric  acid,  is  known  in  the 
works  as  "  nitrous  vitriol " ;  it  is  sent  to  the  Glover  tower,  where  it 
is  diluted  with  water,  or  chamber  acid,  till  its  specific  gravity  is 
about  1.6.  It  then  passes  down  the  Glover  tower,  coming  in  contact 
with  the  hot  sulphur  dioxide  from  the  burners  and  steam  from  the 
lower  part  of  the  tower.  The  high  temperature  causes  the  dilute 
acid  to  give  out  its  absorbed  nitrous  gases,  which  mix  with  the 
sulphur  dioxide  and  pass  back  into  the  lead  chambers.  This  pro- 
cess is  called  denitration  of  the  tower  acid.  The  heat  in  the  lower 
part  of  the  Glover  tower  evaporates  a  considerable  portion  of  the 
water  from  the  acid,  thus  concentrating  it  again  to  a  strength  suffi- 
cient for  use  in  the  Gay-Lussac  tower,  to  which  the  required  amount 
is  returned,  and  the  remainder  is  added  to  the  acid  which  has  been 
concentrated  in  the  lead  pans  (p.  56). 

The  hot  burner  gases  are  cooled  by  contact  with  the  tower  acid 


SULPHURIC   ACID  55 

in  the  Glover  tower  to  50°  to  60°  C. ;  the  best  temperature  at  which 
to  work  the  first  chamber  is  50°  to  65°  C. 

If  the  nitrogen  oxides  are  allowed  to  go  to  waste  entirely,  about 
11  to  13  kilos  of  sodium  nitrate  must  be  used  with  each  100  kilos  of 
sulphur  burned.  The  recovery  process  by  means  of  the  Glover  and 
Gay-Lussac  towers  reduces  this  consumption  of  nitrate  to  about 
4  kilos  per  100  kilos  of  sulphur,  while  a  larger  quantity  of  nitrous 
oxides  is  introduced  into  the  chambers,  causing  the  acid  to  form 
more  rapidly  and  in  greater  quantities. 

Some  manufacturers  prefer  to  supply  the  nitrogen  oxides  in  the 
form  of  liquid  nitric  acid,  introduced  into  the  chambers.     This  is 
easily  regulated,  admits  no  excess  of  air,  and  causes  no  loss  of  sul- 
phur dioxide,  such  as  may  happen  during  the  introduction  of  the! 
"  nitre."     But  much  care  must  be  taken  that  the  nitric  acid  does  notl 
run  down  the  sides  of  the  lead  chamber,  nor  collect  in  the  acid  on! 
the  floor,  for  then  the  lead  is  rapidly  corroded.     Sometimes  the 
nitric  acid  is  introduced  into  the  Glover  tower  with  the  tower  acid. 
The  cost  of  making  and  condensing  the  nitric  acid  must  be  balanced 
against  the  advantages  gained  by  its  use. 

When  sodium  nitrate  is  decomposed  by  sulphuric  acid  in  the 
nitre  pots,  the  nitric  acid  vapor  enters  the  bottom  of  the  Glover 
tower  with  the  sulphur  dioxide.  Tne  vapors  here  coming  in  contact 
with  steam  begin  to  react  at  once,  probably  as  follows  :  — 

2  S02  +  2  HlsrOs  +    H20  =  2  H2S04  +  N203 ; 
or,  3  S02  +  2  HN03  +  2  H2O  =  3  H2S04  +  2  NO. 

Thus  the  process  of  acid  making  begins  in  the  Glover  tower,  and 
is  continued  in  the  chambers  according  to  the  reactions  already  given 
on  p.  46. 

The  nitre  pots  are  fixed  under  a  hopper  through  which  the  nitre 
is  introduced.  The  sulphuric  acid  for  decomposing  the  nitre  is  run 
into  the  pots  through  a  pipe,  sufficient  being 
used  to  form  the  acid  sodium  sulphate 
(NaHS04).  This  is  liquid  at  the  temperature 
of  the  flue,  and  after  the  reaction  is  ended 
can  be  easily  run  out  through  a  pipe  attached 
to  the  bottom  of  the  pot.  On  cooling,  this  acid 
sulphate  solidifies,  forming  "nitre  cake  "  (p.  115).  FlG-  24< 

Compressed  air  is  employed  to  force  the  concentrated  acid  from 
the  Glover  tower  to  the  top  of  the  Gay-Lussac,  and  the  nitrous 
vitriol  from  the  Gay-Lussac  to  the  top  of  the  Glover  tower.  The 
acid  collects  in  a  large  oval  vessel  of  cast  iron  called  the  acid  egg 


56 


OUTLINES   OF  INDUSTRIAL   CHEMISTRY 


(Fig.  24),  and  the  compressed  air  from  (B)  forces  it  out  through,  the 
pipe  (A)  to  the  Glover  or  Gay-Lussac  tower. 

The  "air-lift"  pump  (Fig.  25)  is  now  used  to  some  extent  to 
raise  the  acid  to  the  top  of  the  towers.  A  pipe  (P)  is  sunk  into  the 
ground  to  a  depth  equal  to  the  height  to  which  the  acid  from  (S) 
is  to  be  raised;  the  air  from  (R)  is  forced  in  near  the  bottom  of  the 
pipe,  the  pressure  causing  a  rush  of  air  up  the  pipe,  carrying  before 
it  some  of  the  acid,  which  is  thus  thrown  out  into  (T)  in  "  slugs," 

and  not  in  a  continuous 
stream. 

The  manufacture  of 
chamber  acid  is  shown 
in  the  diagram  in  Fig.  26. 
The  acid  condensed  in 
the  lead  chambers  varies 
from  1.5  to  1.62  sp.  gr. 
If  more  concentrated,  it 
will  absorb  oxides  of  ni- 
trogen present  in  the 
chambers,  and  its  action 
on  the  lead  becomes 
serious.  If  the  chamber 
acid  is  weak,  much  con- 


centration is  necessary  to 
produce  a  commercial 
acid.  As  a  rule,  all  cham- 
ber acid  is  evaporated 
to  a  density  of  170°  sp. 
gr.  (60°  Be.)  in  shallow 
lead  pans  placed  over  and 
heated  by  the  waste  heat 
from  the  pyrites  burners  or  platinum  stills.  Since  acid  stronger 
than  1.70  attacks  the  lead,  "  oil  of  vitriol "  is  concentrated  in  glass 
balloons  or  in  platinum  stills. 

Glass  stills  placed  on  sand  baths  and  heated  by  a  fire  are  used 
somewhat,  and  yield  a  very  pure,  colorless,  and  strong  acid;  but 
owing  to  breakage  there  is  much  loss  and  some  danger. 

Platinum  stills  (Fig.  27)  are  usually  shallow  platinum  dishes 
(S,  S)  covered  with  a  lead  hood  or  bell  (B),  which  is  kept  cool  by 
a  water  jacket.  The  vapors  condensing  in  this  hood  as  a  dilute  acid 
do  not  fall  back  into  the  still,  but  collect  in  a  narrow  trough  around 
the  lower  edge  of  the  bell,  and  are  usually  returned  to  the  lead  pans 


FIG.  25. 


SULPHURIC    ACID 


57 


FIG.  27. 


or  concentrated  in  the  Glover  tower.  When  the  acid  in  the  still 
reaches  a  density  of  1.835  sp.  gr.  (66°  Be.),  it  is  drawn  off  through 
a  platinum  or  lead  cooling  apparatus  (C),  and  thence  into  the  car- 
boys as  "oil  of  vitriol." 

Sometimes  platinum  stills  having  a  spiral  partition  in  the  pan 
are  used;  in  these  the 
dilute  acid  is  compelled 
to  flow  a  considerable 
distance  over  the  hot 
still-bottom  before  it 
escapes  through  a  tube 
leading  from  the  central 
compartment.  The  rate 
of  flow  through  the  still 
determines  the  density 
of  the  acid. 

The  platinum  stills  are  set  directly  over  coke  or  coal  fires  on 
the  grate  (G),  and  are  not  allowed  to  cool  except  for  repairs.  If 
the  chamber  acid  contains  any  nitrous  vitriol,  the  stills  are  rapidly 
destroyed.  To  prevent  this,  it  is  customary  to  add  ammonium  sul- 
phate to  the  acid  during  the  concentration  in  the  lead  pans.  This 
destroys  the  nitrogen  oxides,  thus :  — 

N208  +  (NH4)2S04  =  3  H20  +  H2S04  +  4  K 

Sometimes  the  platinum  is  alloyed  with  iridium  to  render  it  more 
resistant  to  the  action  of  nitrous  vitriol. 

A  still  invented  by  Herseus*  consists  of  platinum  lined  with  a 
layer  of  pure  gold  rolled  with  the  platinum,  and  not  electroplated. 
This  resists  the  action  of  the  concentrated  acid  better  than  the 
platinum. 

When  chamber  acid  is  concentrated  by  running  through  the 
Glover  tower,  it  is  contaminated  with  iron  from  the  flue  dust  of  the 
burners.  It  is  better  to  further  concentrate  such  acid  in  cast-iron 
stills,  since,  when  the  density  reaches  64°  or  65°  Be.,  a  precipitate  of 
ferric  sulphate  forms,  which  may  cake  upon  the  platinum  and  cause 
it  to  crack.  The  acid  intended  for  oil  of  vitriol  is  usually  drawn 
from  the  lead  pans,  while  that  which  has  been  through  the  Glover 
tower  is  frequently  not  further  concentrated. 

In  some  modern  works  the  method  of  making  very  concentrated 
acid  has  been  radically  changed.  A  strong  acid  of  1.6  sp.  gr. 
(55°  Be.)  is  made  in  the  lead  chambers  and  passed  through  the 

*  J.  Soc.  Chem.  Ind.,  1891,  470.    Ibid.,  1803,  122. 


58 


OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


Glover  tower,  where  it  reaches  a  density  of  1.77  sp.  gr.  (63°  Be.). 
It  is  then  concentrated  in  cast-iron  stills  (Fig.  28)  *  to  a  density  of 
1.835  to  1.842  sp.  gr.  (66°  to  66.3°  Be.).  The  pan  acid  enters  through 
the  pipe  (A)  in  a  regulated  stream.  The  concentrated  acid  passes 


FIG.  28. 

out  through  (B)  into  the  vessel  (C),  in  which  any  sediment  (sul- 
phates, etc.)  deposits.  A  concentrated  acid  (98  per  cent  H2S04) 
flows  from  the  spout  at  the  top  of  (C)  into  the  cooling  vessels 
(E,  E).  The  still  is  heated  with  gaseous  fuel  entering  through  (  F). 
Acid  over  1.75  sp.  gr.  has  very  little  action  on  cast  iron,  and  the  stills 
stand  from  two  to  six  months'  constant  use.  Sometimes  instead  of 
pans  or  stills  two  Glover  towers  are  used,  the  acid  being  denitrated 
in  that  next  the  chambers,  and  further  concentrated  to  a  density  of 
63°  to  66°  Be.  in  that  next  the  burners. 

Chamber  acid  is  often  concentrated  in  lead  pans  by  allowing  the 
flame  from  a  coal  fire  or  gas  producer  to  pass  directly  over  the  surface 
of  the  acid.  But  it  may  be  thus  contaminated  with  soot  and  its 
color  become  dark  brown. 

Open  lead  tanks  containing  lead  coils,  heated  by  steam  under 
pressure,  are  sometimes  used  for  acid  concentration  to  60°  Be.  This 
gives  a  clean  product,  but  is  not  so  economical  as  evaporation  by  the 
waste  heat  from  the  burners. 

To  secure  the  very  intimate  mixing  of  the  gases  essential  in  the 
lead  chambers,  Professor  Lunge  invented  his  plate  tower. f  This  is 
a  tall  -tower  lined  with  lead,  and  divided  into  narrow  chambers  by 
transverse  stoneware  plates  (Fig.  29)  perforated  by  small  holes,  and 
so  placed  that  the  holes  are  not  in  line.  By  this  arrangement 
the  gases  and  liquids  are  brought  into  very  close  contact,  and  it  is 
claimed  that  the  chamber  space  for  a  given  yield  of  acid  can  be 
much  reduced.  It  is  recommended  that  such  a  tower  be  placed 
between  each  pair  of  adjoining  chambers,  and  that  the  plates  be 

*  Transactions  of  the  American  Institute  of  Mining  Engineers,  VoL  16,  517. 
W.  H.  Adams. 

t  Zeitschrift  fur  angewandte  Chemie,  1889,  385.    J.  Soc.  Chem.  Ind.,  1889,  774. 


SULPHURIC   ACID 


59 


used  in  the  Gay-Lussac  tower  also.  They  are  not  practicable  for 
the  Glover  tower,  because  the  heat  is  liable  to  crack  them,  and  the 
small  holes  become  clogged  with 
dust.  It  may  be  noted  here  that 
these  Lunge-Euhrmann  "  plate 
towers"  have  found  some  favor 
for  condensing  hydrochloric  acid, 
but  are  said  to  obstruct  the 
draught  in  sulphuric  acid  mak- 
ing. 

The  "pipe  column"1*  invention 
of  Gilchrist  and  Hacker  carries 
out  the  same  idea  of  mixing  the 
gases  more  thoroughly.  It  con- 
sists of  towers  containing  a  num- 
ber of  small  earthenware  or  lead 
pipes  set  horizontally,  and  open- 
to  the  air  at  each  end. 

FIG.  29. 

Another  recent  innovation  in 

sulphuric  acid  making  is  Barbier's  tower  system,t  in  which  the  lead 
chambers  are  abolished  and  a  series  of  towers  substituted  (Fig.  30). 
Sulphur  dioxide  is  led  through  the  towers,  which  are  joined  by  pipes 
(A,  A)  leading  from  the  top  of  one  to  the  bottom  of  the  next.  The 

towers  are  filled  with 
perforated  pottery  ves- 
sels, affording  a  large 
surface  exposure.  Di- 
lute nitric  acid  is  sup- 
plied to  each  tower  by 
a  sprinkler  at  the  top. 
Beneath  the  towers  are 
pans  (B,  B)  for  collect- 
ing the  acid  as  it  forms. 
These  are  placed  over 
a  flue  leading  from  a 
grate  at  the  lower  end 
of  the  series,  and  so 

arranged  that  the  overflow  from  one  pan  passes  into  the  next.  The 
acid  thus  flows  toward  the  fire,  becoming  more  concentrated  in  each 
pan.  The  water  vapor  and  nitrous  gases  from  each  pan  go  directly 
back  into  the  tower  above  it.  The  last  two  or  three  pans  are  not 
*  J.  Soc.  Ctiem.  Ind.,  1894,  1142.  t  Bui.  Soc.  Chim.,  11,  726. 


FIG 


60  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

under  towers,  and  in  these  the  acid  is  concentrated  to  about  60°  Be. 
by  direct  heat  from  a  fire,  the  denitration  being  effected  at  the  same 
time.  The  last  tower  of  the  series  is  a  Gay-Lussac  for  saving  the 
nitrous  vapors.  The  chief  advantages  claimed  for  this  system  are  :  it 
occupies  less  ground  and  is  cheaper  to  build  than  the  lead  chambers ; 
it  works  at  90°  C.,  hence  atmospheric  changes  have  less  influence  on 
the  process,  and  it  is  suitable  for  use  in  hot  or  cold  climates  ;  and  that 
it  gives  a  greater  yield  of  acid  per  cubic  meter  of  space  than  does 
the  chamber  system.  Although  some  unfavorable  results  with  this 
method  have  been  reported,*  it  does  seem  that  great  developments 
in  tower  systems  may  be  expected  in  the  near  future.  A  substitute 
for  the  cumbersome  and  expensive  lead  chamber  is  much  to  be  desired. 

When  zinc  blende  or  copper  mattes  are  roasted,  muffle  furnaces 
externally  heated,  sometimes  by  generator  gas,  are  used,  as  the 
amount  of  sulphur  in  the  ore  is  insufficient  for  the  combustion. 
These  furnaces  contain  shelves,  and  are  a  modified  form  of  shelf 
burner,  the  shelves  being  in  the  muiEe.  Sometimes  mechanical 
rakes  are  used  to  draw  the  charge  down  from  shelf  to  shelf. 

Very  concentrated  acid  is  now  made  by  artificially  cooling  oil  of 
vitriol  of  66.3°  Be.  considerably  below  0°  C.  Under  such  condi- 
tions crystals  of  sulphuric  a"cid  (rnonohydrate)  separate.  These  are 
quickly  freed  from  mother-liquor  by  means  of  a  centrifugal  machine. 
The  crystals  melt  at  10°  C.,  and  yield  an  acid  of  99.5  per  cent 
H2S04,  containing  only  a  trace  of  moisture. 


FUMING   SULPHURIC   ACID 

This  is  prepared  by  the  dry  distillation  of  sulphate  of  iron. 
Copperas  (FeS04  •  7  H20)  is  gently  heated  in  the  air  until  the  water 
is  all  expelled  and  part  of  the  ferrous  sulphate  is  oxidized  to  the 
ferric  state.  The  mixture  of  sulphates  is  then  put  into  small  iron 
retorts,  which  are  heated  in  a  furnace.  Decomposition,  according 
to  the  following  equation,  ensues :  — 

Fe2(S04)3  -  2  FeS04  =  2  Fe203  +  4  S03  +  S02. 

The  vapors  of  sulphur  dioxide  and  sulphuric  anhydride  are  con- 
densed in  receivers  containing  oil  of  vitriol,  which  dissolves  them. 
The  Nordhausen  acid  thus  formed  is  a  brown  oily  liquid,  fuming  in 
the  air,  owing  to  the  escape  of  the  dissolved  sulphur  oxides.  By 
cooling  to  0°  C.,  crystals  of  pyrosulphuric  acid  (H2S207)  separate. 

Nordhausen  acid  is  now  chiefly  produced  in  Bohemia,  where  a 

*  J.  Soc.  Chem.  Ind.,  1895,  698. 


SALT  61 

pyritiferous  shale  is  found,  which,  when  weathered,  forms  a  basic 
sulphate  of  iron,  that  is  dried  and  distilled. 

REFERENCES 

J.  Soc.  Chem.  Ind.,  1882-1898  +. 

Progress  in  the  Concentration  of  Oil  of  Vitriol.  By  W.  H.  Adams,  Transactions 
of  the  American  Institute  of  Mining  Engineers,  1887-1888.  Vol.  16, 
p.  496. 

Sulphuric  Acid  and  Alkali.     Vol.  I.    2d.  Ed.     G.  Lunge,  London,  1891. 

Mineral  Industry.     Vols.  I-V,  1892-1896. 

Schwefelsaurefabrication.    Dr.  K.  W.  Jurisch,  Stuttgart,  1893. 


SALT 

The  sources  of  salt  are :  — 

1.  Sea-water. 

2.  Eock  salt. 

3.  Salt  brines  derived  from  springs,  lakes,  or  wells. 

Atlantic  sea-water,  except  near  the  mouths  of  large  rivers,  aver- 
ages about  3.4  per  cent  of  solid  matter,  of  which  about  75'  per  cent 
is  sodium  chloride,  the  remainder  consisting  of  chlorides,  bromides, 
and  sulphates  of  potassium,  magnesium,  calcium,  lithium,  etc.,  with 
minute  amounts  of  other  salts. 

The  concentration  of  sea-water  for  salt  is  carried  on  to  some  ex- 
tent in  warm,  dry  countries  by  solar  evaporation,  the  water  usually 
being  exposed  in  shallow  tanks  or  ponds  to  the  full  force  of  the 
sun's  rays.  Sea-water  is  seldom  evaporated  over  fire  because  of  the 
cost  of  fuel.  In  Russia  it  is  allowed  to  freeze  over  the  surface,  and 
the  ice,  which  contains  but  little  salt,  is  removed.  This  is  repeated 
until  the  brine  is  sufficiently  concentrated  to  make  the  evaporation 
over  fire  profitable.  Salt  made  from  sea-water  ("sea-salt")  is 
very  coarse  and  is  usually  damp,  owing  to  the  presence  of  some 
magnesium  chloride,  which,  being  a  deliquescent  substance,  attracts 
moisture  from  the  air.  It  is  of  less  importance  in  this  country 
than  that  made  from  other  brines;  the  greater  part  of  the  sea-salt 
produced  here  in  1894  was  made  in  California. 

Rock  salt  is  found  in  many  countries,  and  often  very  pure.  In 
Austria,  Germany,  Spain,  and  Louisiana  it  occurs  in  large  deposits, 
so  pure  that  it  is  only  necessary  to  grind  it  for  use,  but  in  most 
cases  it  is  contaminated  with  iron  oxides,  clay,  sand,  and  other  im- 
purities, which  often  necessitate  its  purification.  In  this  country  it 
is  mined  in  New  York,  Kansas,  California,  Utah,  and  Louisiana. 


Tl  B  R  A 


62  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

As  it  does  not  dissolve  so  readily  as  finely  crystallized  salt,  it  is 
preferred  for  many  purposes,  such  as  curing  meat,  preserving  green 
hides,  and  feeding  to  live  stock. 

The  salt  of  principal  interest  in  this  country  is  derived  from 
natural  brines,  found  chiefly  in  New  York,  Michigan,  Kansas,  and 
Ohio,  while  West  Virginia,  Utah,  Texas,  and  Pennsylvania  produce 
lesser  quantities. 

The  New  York  deposits  are  near  Syracuse  and  in  the  neighbor- 
hood of  Warsaw  and  Batavia.  The  Onondaga  (Syracuse)  deposit  has 
been  known  since  the  middle  of  the  seventeenth  century,  and  since 
1797  has  been  the  property  of  the  state.  That  at  Warsaw,  opened 
in  1883,  is  now  the  most  important.  The  Michigan  deposits  are 
near  Saganaw  Bay  and  Manistee,  a  strong  brine  being  obtained  by 
boring.  Large  amounts  of  brine  are  evaporated  near  Salina,  Kan- 
sas. The  Ohio  and  West  Virginia  deposits  are  in  the  valley  of  the 
Ohio  Eiver,  near  Pomeroy  and  Wheeling. 

In  the  Onondaga  district,  the  brine  is  obtained  by  boring  wells, 
8  inches  in  diameter  and  from  300  to  350  feet  deep,  and  lined 
with  iron  casings  to  exclude  surface  water.  The  state  owns  and 
operates  these  wells,  furnishing  the  brine  to  the  salt  makers,  and 
collecting  a  tax  of  one  cent  per  bushel  of  the  salt  made.  This  plan 
is  not  profitable  to  the  state  at  present,  and  it  is  not  improbable  that 
the  reservation  may  be  sold. 

The  brine  is  raised  by  pumps,  worked  by  an  endless  wire  rope, 
the  power  being  furnished  by  an  engine.  As  it  comes  from  the 
pumps  the  brine  has  a  slightly  turbid  appearance,  due  to  clay  or  fine 
sand  raised  from  the  well,  together  with  minute  bubbles  of  carbon 
dioxide,  with  which  the  brine  is  charged.  It  also  contains  some 
ferrous  carbonate,  which  is  held  in  solution  by  the  carbon  dioxide. 
As  the  latter  escapes,  the  ferrous  salt  absorbs  oxygen  from  the  air, 
and  hydrated  ferric  oxide  separates  as  a  yellowish  red  turbidity, 
which  settles  after  a  time,  leaving  the  brine  perfectly  clear. 

For  the  manufacture  of  "solar  salt,"  of  which  a  considerable 
quantity  is  still  made  at  Syracuse,  three  sets  of  tanks  are  used. 
The  first  are  called  "  deep  rooms  " ;  here  the  brine  is  received  from 
the  pump-house,  and  the  ferric  hydroxide  and  sediment  deposit.  The 
clear  brine  is  then  drawn  into  the  "  lime  rooms,"  —  tanks  about  8 
inches  deep,  18  feet  wide,  and  from  100  to  400  feet  long.  In  these 
the  evaporation  by  the  sun's  rays  goes  on  until  small  crystals  of  salt 
appear.  The  brine  contains  calcium  sulphate  and  chlorides  of  cal- 
cium and  magnesium.  The  calcium  sulphate  deposits  as  gypsum 
(CaS04  •  2  H20),  in  long  slender  crystals,  usually  in  clusters ;  but  a 


SALT 


63 


small  portion  remains  in  solution  with  the  salt.  The  concentrated 
brine  is  then  drawn  into  the  "salt  rooms,"  which  are  very  similar 
to  the  lime  rooms,  but  only  about  6  inches  deep.  In  these  the  salt 
is  deposited,  more  brine  being  admitted  as  the  water  evaporates, 
until  the  layer  of  salt  on  the  vat  floor  is  about  3  inches  deep. 
About  three  times  in  a  season  the  salt  is  "  harvested " ;  i.e.  it  is 
raked  together  and  put  into  tubs  having  perforated  bottoms,  through 
which  the  mother-liquor  drains  off.  It  is  then  taken  to  the  store- 
house, where,  according  to  the  New  York  law,  it  must  drain  14  days 
before  being  marketed. 

All  the  vats  are  built  of  wood  and  provided  with  movable  covers 
to  keep  out  rain.  During  fair  weather  these  are  rolled  back.  The 
vats  are  built  on  piles,  so  that  the  "  deep  rooms  "  stand  higher  than 
the  "lime  rooms,'7  and 
these  in  turn  are  higher 
than  the  salt  vats ;  thus 
the  liquor  runs  by  grav- 
ity from  one  set  to  the 
next. 

The  mother-liquors 
contain  considerable 
quantities  of  calcium 
and  magnesium  chlo- 
rides. 

The  large  cubical 
salt  crystals  are  usu- 
ally not  perfect;  they 
are  skeleton  crystals,  with  the  edges  nearly  complete,  but  with  cavi- 
ties in  the  crystal  faces.  This  makes  the  salt  more  bulky  than  is 
the  case  with  fine  solid  crystals.  Moreover,  the  cavities  hold  small 
drops  of  the  mother-liquor,  even  after  draining  for  some  days ;  con- 
sequently, calcium  and  magnesium  chlorides  remain  in  the  salt,  and 
these  being  deliquescent,  cause  it  to  become  moist  in  damp  weather. 

In  some  foreign  countries,  dilute  brine  is  concentrated  by  flow- 
ing over  brushwood  "  ricks,'7  prior  to  final  solar  evaporation  (p.  3). 

Where  brine  is  concentrated  by  the  use  of  fuel,  the  product  is 
generally  called  "boiled  salt."  This  is  prepared  in  several  ways. 
By  the  Kettle  Process,  Fig.  31,*  the  brine  is  evaporated  in  cast-iron 
kettles  (A,  A)  about  4  feet  in  diameter  by  2  feet  deep.  They  are 
set  in  rows  of  from  16  to  25,  over  a  flue  leading  from  the  fire  box 
(G)  to  the  chimney.  The  contents  of  the  kettles  near  the  fire  boil 
*  After  Merrill,  Bui.  N.  Y.  State  Museum,  III,  No.  11. 


FIG.  81. 


64  OUTLINES   OF  INDUSTRIAL   CHEMISTRY 


down  rapidly  and  produce  small  dense  crys- 
tals, but  in  those  near  the  chimney,  evaporation 
is  slow,  and  large  crystals  similar  to  solar  salt 
are  formed.  The  two  products  are  generally 
mixed  and  sold  as  "common  fine  salt."  The 
brine  coming  from  the  wells  must  be  purified 
by  adding  "milk  of  lime,"  and  stirring  well, 
otherwise  the  product  will  be  colored  by  ferric 
hydroxide.  The  lime  combines  with  the  carbon 
dioxide  and  precipitates  the  iron.  After  set- 
tling, the  brine  is  supplied  to  each  kettle  by 
a  wooden  pipe  (P).  The  first  effect  of  heating 
and  concentrating  the  brine  is  the  separation 
of  "  bittern,"  consisting  of  calcium  sulphate  and 
a  little  magnesium,  sulphate.  This  is  removed 
by  the  bittern  pan  (B),  a  shallow  wrought-iron 
dish,  somewhat  like  a  frying  pan  with  very 
sloping  sides  and  a  vertical  handle  near  the  cen- 
tre. Its  sides  fit  closely  against  the  walls  of  the 
kettle ;  as  the  bittern  collects  in  the  pan,  the  latter 
is  emptied  and  replaced  several  times ;  but  as  soon 
as  the  salt  crystals  begin  to  form,  it  is  removed. 

Part  of  the  calcium  sulphate,  together  with 
some  salt,  deposits  as  a  scale  on  the  sides  of 
the  kettle.  This  incrustation  soon  becomes  so 
thick  that  it  causes  loss  of  heat,  and  it  is  removed 
by  filling  the  kettle  with  fresh  water,  which 
dissolves  the  salt,  leaving  the  calcium  sulphate 
so  porous  that  it  is  easily  scraped  away.  This 
deposit  collects  faster  in  the  front  kettles  than 
in  those  nearer  the  chimney;  when  the  latter 
become  coated,  it  is  customary  to  shut  down 
the  entire  system  and  clean  them  all.  The  salt 
is  removed  as  it  separates,  and  drained  for  a 
short  time  in  baskets  (D)  placed  over  the  kettles ; 
it  is  then  dumped  into  the  storage  bins  (E), 
where  it  must  remain  14  days. 

The  salt  block,  as  the  plant  is  called,  is  in 
continuous  operation,  night .  and  day,  for  about 
14  days,  two  "  runs "  being  made  each  month. 
A  good  average  "run"  at  Syracuse  produces 
about  7800  bushels  of  salt. 


SALT  65 

Sometimes  the  kettles  are  heated  by  steam  jackets ;  as  all  have 
the  same  steam  pressure  the  temperature  is  uniform,  and  only  one 
quality  of  salt  is  produced,  v, 

Salt  is  also  made  by  the  "pan  process"  (Fig.  32),*  of  direct 
evaporation  over  fire.  Large  wrought-iron  pans  (H,  H),  24  feet 
wide,  100  feet  long,  and  12  inches  deep  are  used.  These  pans  are 
divided  into  two  sections  by  a  loose  partition,  which  allows  the 
brine  to  flow  slowly  from  the  rear  to  the  front  section.  A  second, 
smaller  pan  is  set  behind  and  slightly  above  the  first,  so  that  its 
contents  may  be  syphoned  into  the  front  pan.  Both  are  heated  by 
flues  from  grates  (G),  but  the  rear  one  gets  only  the  waste  heat, 
before  the  gases  pass  into  the  chimney.  The  ends  of  each  pan  are 
made  perpendicular  to  the  bottom,  but  the  sides  are  inclined,  and 
sloping  wooden  platforms  (F,  F),  called  '-'drips,"  are  joined  to  them ; 
on  these  the  salt  is  drained  when  removed  from  the  pans.  The 
brine  is  purified  with  "  milk  of  lime,"  as  in  the  kettle  process. 

The  pan  process  permits  an  easy  control  of  the  size  of  the  grain. 
For  the  preparation  of  a  very  fine  grained  product,  called  "  factory 
filled  salt,"  it  is  customary  to  add  a  small  amount  of  sodium  carbon- 
ate to  the  brine ;  this  decomposes  the  chlorides  of  calcium  and  mag- 
nesium and  any  excess  of  caustic  lime  from  the  "  liming."  Then  a 
small  quantity  of  butter,  glue,  or  soft  soap  is  added,  and  forms  an 
insoluble  calcium  soap 
with  the  remaining  traces 
of  lime,  and  this  is  re- 
moved  by  skimming. 

For  both  the  kettle 
and  the  pan  process,  coal 
dust  is  used  as  fuel. 

In  Michigan  and  in 
western  New  York,  brine 

is  evaporated  in  "  grainers  "  (Fig.  33)  * ;  these  are  long,  shallow  vats 
of  wood  or  iron,  containing  steam  pipes  (P,  P),  through  which  live  or 
exhaust  steam  is  passed.  The  pipes  are  about  4  inches  in  diameter 
and  are  hung  about  6  inches  above  the  floor  of  the  "  grainer,"  which  is 
some  20  inches  deep.  Once  a  day  the  salt  is  raked  up  and  deposited 
on  draining  platforms  over  the  grainers.  The  brine  is  purified  before 
evaporation,  as  in  the  pan  process,  and  is  supplied  to  the  grainer  in 
just  sufficient  quantities  to  replace  the  water  evaporated.  When  the 
mother-liquors  become  too  highly  charged  with  calcium  and  mag- 
nesium chlorides,  they  are  drawn  into  special  grainers,  and  a  low 
grade  of  salt  is  made  from  them. 

*  After  Merrill,  Bui.  N.  Y.  State  Musuem,  III,  No.  11. 


66  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

Brine  is  sometimes  evaporated  in  vacuum  pans,  and  a  very  finely 
crystalline  product,  the  best  grade  of  table  and  dairy  salt  results. 
It  is  separated  from  adhering  mother-liquor  by  the  centrifugal 
machine. 

Strong  brine  boils  at  105°-109°  C.,  and  so  cannot  be  boiled  by  free 
steam,  although  evaporation  of  very  dilute  brine  can  be  slowly  accom- 
plished in  this  way.  The  heat  in  the  kettle  and  pan  process  is  suf- 
ficient to  dehydrate  any  calcium  sulphate  in  the  salt ;  when  dissolved 
in  water,  such  products  cause  a  slight  milkiness  which  disappears 
after  a  time,  owing  to  the  hydration  of  the  calcium  sulphate  and  its 
solution  in  the  water. 

Sometimes  pure  water  is  introduced  into  rock  salt  deposits  through 
tube  wells ;  when  saturated  with  salt,  it  is  pumped  to  the  surface 
and  evaporated.  A  much  stronger  brine  than  is  found  in  nature  is 
secured  in  this  way. 

In  some  places,  chiefly  in  West  Virginia  and  in  Germany,  large 
quantities  of  bromine  are  recovered  from  the  mother-liquors  (also 
called  "  bittern  ")  from  the  salt  industry. 

In  Italy,  Austria,  and  China  the  manufacture  and  sale  of  salt  is 
a  government  monopoly.  In  France,  Germany,  and  India  salt  used 
for  seasoning  food  is  subject  to  tax.  When  used  for  technical  pur- 
poses, or  in  agriculture,  the  tax  is  very  small.  To  prevent  fraud, 
all  German  salt,  not  intended  for  table  use,  must  be  mixed  with  cer- 
tain substances  to  render  it  unfit  for  eating.  Some  of  these  adulter- 
ants are  iron  oxide,  crude  petroleum,  coal  dust,  pyrolusite,  carbolic 
acid,  mineral  acids,  sodium  sulphate  or  carbonate,  alum,  soot,  etc. 


REFERENCES 

Die  Industrie  von  Stassfurt  und  Leopoldshall.     Dr.  G.  Krause,  Cothen,  1877. 
Report  on  Manufacture  of  Chemical  Products  and  Salt.     W.  L.  Rowland, 

United  States  Census,  1880  ;  Washington,  1884. 
Mineral  Resources  of  the  United  States.     (1882-1893.) 
Chemische  Industrie.     1883,  225.     G.  Lunge. 

Report  of  the  State  Geologist  of  New  York,  1885,  pp.  12-47.    I.  P.  Bishop. 
Journal  of  the  Society  of  Chemical  Industry,  1888,  660.     On  the  Tees  Salt 

Industry.     T.  W.  Stuart. 

Die  Salz  Industrie  von  Stassfurt.    Dr.  Precht,  1889.     (Weicke,  Stassfurt.) 
Bulletin  of  the  New  York  State  Museum,  Vol.  Ill,  No.  11.     Salt  and  Gypsum 

Industries  of  New  York.     F.  J.  H.  Merrill,  Albany,  1893. 
Forty-seventh  Report  of  the  State  Museum  of  New  York,  pp.  205-257.     The 

Livonia  Salt  Shaft.    James  Hall,  1894. 
Journal  of  the  Society  of  Arts,  1894.    Manufacture  of  Salt.    F.  Ward. 


HYDROCHLORIC   ACID   AND   SODIUM  SULPHATE 


67 


HYDROCHLORIC  ACID  AND  SODIUM  SULPHATE. 

Hydrochloric  or  muriatic  acid  is  generally  made  by  the  action  of 
sulphuric  acid  on  common  salt.  It  is  a  by-product  of  the  Leblanc 
soda  process,  and  in  the  early  years  of  the  industry  was  allowed  to 
escape  into  the  air,  as  the  demand  for  it  was  small.  But  the 
nuisance  caused  by  the  acid  fumes  in  the  neighborhood  of  the 
alkali  works  became  so  great,  that  in  England  a  very  stringent 
law  was  enacted  forbidding  the  soda  makers  to  allow  more  than 
5  per  cent  of  the  gas  to  escape  into  the  atmosphere.  This  made  it 
necessary  to  absorb  the  acid  fumes  in  water.  The  provisions  of  the 
present  "  Alkali  Act "  permit  only  0.2  grain  of  hydrochloric  acid  per 
cubic  foot  of  chimney  gas  to  be  discharged  into  the  atmosphere. 

The  Leblanc  industry  has  declined  in  recent  years,  but  there 
is  an  increased  demand  for  hydrochloric  acid,  and  at  present 
this  is  one  of  the  main  products  desired.  Its  chief  use  is  for  the 
generation  of  chlorine  for  the  manufacture  of  bleaching  powder; 
now  nearly  all  soda  makers  also  produce  bleaching  powder,  and  the 
profits  derived  from  the  latter  have  largely  offset  the  decline  in 
returns  from  soda-ash.  Up  to  the  present,  no  better  method  than 
the  above  has  been  devised  for  making  this  acid.  The  process  may 
be  represented  by  the  equation  :  — 

2  NaCl  +  H2S04  =  Na2S04  +  2  HC1. 

But  as  actually  carried  out  it  takes  place  in  two  stages,  according 
to  the  following  reactions  :  — 

1)  NaCl  +  H2S04  =  NaHS04  +  HC1. 

2)  NaHS04  +  NaCl  =  Na2S04  +  HC1. 

These  reactions  may  be  carried  out  by  heating  the  mixture  of 
salt  and  sulphuric  acid  either  in  an  "  open  roaster,"  or  in  a  muffle  or 
" close  roaster."  These  are  both  called  "salt-cake  furnaces." 


£3^v-     : 


The  open  roaster  (Fig.  34)  consists  of  two  parts,  the  cast-iron 
pan  (A)  and  the  reverberatory  hearth  (C).     The  salt  and  sulphuric 


68 


OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


acid  (60°  Be.,  sp.  gr.  1.72)  are  put  into  the  pan  (A),  and  are  moder- 
ately heated  by  a  coke  fire  on  the  grate  (E).  The  first  reaction 
takes  place  at  a  comparatively  low  heat,  and  the  hydrochloric  acid 
vapors  escape  through  the  earthenware  pipe  (B).  Then  the  fused 
mass  of  sodium  acid  sulphate  and  undecomposed  salt  is  raked  up  on 
the  reverberatory  hearth  (C),  where  it  is  exposed  to  the  high  tem- 
perature of  the  flame  from  (D).  This  completes  the  second  reaction, 
and  a  pasty  mass  of  normal  sodium  sulphate  is  formed.  The  hydro- 
chloric acid  vapors,  set  free  during  the  reaction,  mix  with  the 
furnace  gases  from  (D),  and  escape  through  the  pipe  (F)  to  the 
absorbing  apparatus.  The  furnace  gases  dilute  the  acid  vapors 
so  much,  that  a  very  concentrated  solution  of  hydrochloric  acid 
cannot  be  made  with  the  open  roaster;  however,  it  yields  acid 
strong  enough  for  use  in  Weldon's  chlorine  process  (p.  96).  More- 
over, the  soot  and  dust  from  the  furnace  at  (D)  contaminate  the 
acid,  and  may  cause  clogging  in  the  passages  and  pipes  of  the 
absorption  apparatus.  The  open  roaster  has  the  advantage  over 
the  close  roaster,  that  it  yields  more  sodium  sulphate  with  smaller 
consumption  of  fuel.  The  crude  sodium  sulphate,  called  "  salt- 
cake,"  usually  contains  a  little  undecomposed  salt  and  a  slight 
excess  of  sulphuric  acid. 

The  muffle  or  "close  roaster ;>   is  used  very  generally  on  the 
continent  of  Europe,  and  yields  a  stronger  and  purer  acid  than 


FIG.  35. 


the  open  roaster.  The  usual  form  is  shown  in  Fig.  35,  The  pan 
(A)  is  built  very  much  as  in  the  open  roaster,  but  is  heated  by  the 
furnace  gases  from  the  grate  (D).  The  acid  vapors  set  free  in 
the  pan  escape  by  the  pipe  (C)  to  the  absorption  apparatus.  The 
muffle  (B)  is  made  of  fire-clay  or  brick,  arid  is  heated  by  the  flames 
from  the  grate  (D).  The  mixture  of  acid  sulphate  and  salt  is  raked 
from  the  pan  (A)  into  the  muffle  (B),  where  it  is  heated  to  a  red 
heat,  and  the  acid  vapor  liberated  passes  through  the  pipe  (E)  to 
the  absorption  apparatus.  In  this  form  of  roaster,  the  soot  and  dust 
from,  the  grate  are  kept  away  from  the  acid  vapor.  Also,  a  very 
concentrated  acid  vapor  is  obtained,  which  favors  the  formation  of 


HYDROCHLORIC   ACID   AND   SODIUM   SULPHATE 


69 


a  concentrated  solution  of  hydrochloric  acid  in  the  absorbers.  But 
the  muffles  are  expensive  to  build,  yield  a  smaller  output  of  salt- 
cake,  and  require  more  fuel  than  the  open  roaster.  Moreover,  they 
very  often  crack,  thus  permitting  acid  vapors  to  escape  into  the  flues 
and  chimney>  causing  loss  and  creating  a  nuisance.  It  is  customary 
to  maintain  a  slight  pressure  in  the  flues  and  chimney,  so  that 
if  the  muffle  cracks,  the  flue  gases  force  their  way  into  it.  This 
may  cause  a  slight  contamination  of  the  acid,  but  no  nuisance  is 
created.  Cheaper  fuel  may  be  used  with  these  furnaces,  but  repairs 
are  apt  to  be  expensive. 

The  pan  (A)  in  both  furnaces  is  about  10  feet  in  diameter, 
7  inches  thick  at  the  centre  and  3  inches  thick  at  the  sides.  After 
a  charge  is  drawn,  the  pan  is  cooled  somewhat  before  introducing 
another,  for  cold  salt,  coining  in  contact  with  the  hot  pan,  might 
crack  it.  The  sulphuric  acid  is  generally  heated  to  100°  or  130°  C. 
for  the  same  reason. 

During  the  second  reaction,  the  charge  is  constantly  stirred  with 
a  "  rabble,"  a  large  hoe-shaped  tool,  to  prevent  tf  crusting "  or  burn- 
ing on  to  the  hearth  or  retort.  The  stirring  is  done  by  workmen, 
and  as  the  work  is  very  heavy,  they  are  sometimes  careless,  and 
allow  a  crust  to  form,  which  may  crack  the  muffle.  Consequently, 
many  attempts  have  been  made  to  construct  mechanical  stirrers. 


FIG.  Sfi. 

The  Mactear  furnace*  (Fig.  36)  t  is  the  only  one  of  these  that  has  met 
with  much  success.  This  is  a  reverberatory  furnace  with  a  rotating 
hearth  (A);  in  the  centre  of  the  hearth  is  a  shallow  pan  (B)  into 
which  the  mixture  of  salt  and  sulphuric  acid  is  run  in  a  slow, 
continuous  stream.  The  mass  overflows  on  to  the  hearth,  where 
it  is  subjected  to  the  high  heat  of  the  flames  from  the  grate  (G) ;  at 


*  Chemische  Industrie,  1881,  253. 
t  After  Lunge. 


J.  Soc.  Chera,  Ind.,  1885,  534. 


'0 


OUTLINES  OF  INDUSTRIAL   CHEMISTRY 


the  same  time,  it  is  mixed  and  pushed  towards  the  edge  of  the 
hearth  by  stirrers  (C),  against  which  the  charge  strikes  as  the  hearth 
revolves.  The  speed  is  so  regulated  that  the  salt  is  all  converted 
to  sulphate  by  the  time  it  reaches  the  edge  of  the  hearth.  There  it 
falls  into  an  annular  trough  (D,  D),  which  carries  the  pasty  mass 
out  of  the  furnace.  An  apron  attached  to  the  edge  of  the  hearth 
dips  into  this  trough,  so  that  the  salt-cake  forms  a  lute,  and  pre- 
vents the  escape  of  the  acid  vapor  into  the  space  beneath  the  hearth. 
This  only  imperfectly  protects  the  driving  mechanism  from  the 
flame  and  acid  vapors,  and  serious  difficulties  are  consequently 
incurred  in  running  the  furnace.  More- 
over, the  acid  vapors  are  much  diluted  with 
the  fire  gases,  which  renders  their  absorp- 
tion difficult.  Because  of  these  disadvan- 
tages, some  manufacturers  who  have  tried 
mechanical  appliances  have  abandoned 
them,  and  returned  to  the  hand-worked 
furnace. 

If  a  salt-cake  free  from  iron  is  desired, 
lead  pans  instead  of  cast-iron  ones  are  used. 
But  these  are  easily  overheated  or  injured. 
The  hydrochloric  acid  vapor  is  absorbed 
in  water,  either  by  passing  through  tall 
towers  (Fig.  37)*  filled  with  coke,  over 
which  water  trickles;  or  in  large  earthen- 
ware Woulff  bottles  (bombonnes),  provided 
with  safety-tubes  for  back  pressure,  and 
with  a  coke  tower  at  the  end  of  the  series. 
The  purpose  of  the  tower,  which  is  fed 
by  a  spray  of  water,  is  to  absorb  any  acid 
vapors  which  may  pass  uncondensed  through  the  bombonnes.  These 
are  placed  en  cascade^  and  joined  by  the  side  tubulatures,  so  that  a 
stream  of  water  or  dilute  acid  from  the  tower  will  flow  through 
them  in  a  direction  opposite  to  that  in  which  the  gas  is  moving. 

The  Lunge-Rohrmann  plate  tower  (p.  58)  has  been  tried  with 
some  success  as  a  substitute  for  the  coke  tower  and  bombonnes,  for 
hydrochloric  acid  absorption. 

The  condensation  of  hydrochloric  acid  vapors  is  not  so  simple  a 
process  as  it  at  first  appears.  The  gases  coming  from  the  roasters 

*  After  Lunge. 

t  That  is,  on  a  series  of  steps,  so  that  each  stands  a  few  inches  higher  than  the 
one  preceding. 


FIG.  37. 


HYDROCHLORIC   ACID   AND  SODIUM   SULPHATE          71 

are  very  hot,  and  must  be  cooled  before  they  can  be  absorbed  to  form 
a  strong  acid.  Moreover,  with  open  roasters,  there  is  a  very  large 
amount  of  inert  gas  present  (nitrogen  and  carbon  dioxide  from  the 
fire)  which  dilutes  the  acid  vapors.  Then,  too,  the  vapors  are  not 
set  free  regularly  in  any  roaster,  there  being  a  rapid  evolution  during 
the  progress  of  the  first  reaction,  and  a  much  slower  liberation  dur- 
ing the  second.  This  may  cause  a  temporary  rush  of  vapors  through 
the  apparatus,  so  that  they  cannot  be  properly  taken  up  by  the  water. 

The  ordinary  muriatic  acid  of  trade  is  an  aqueous  solution  of  the 
acid  vapor,  having  a  specific  gravity  of  about  1.20  and  containing 
about  40  per  cent  by  weight  of  dry  hydrochloric  acid  vapor.  It  is 
impure,  containing  sulphuric  acid,  chlorine,  iron  chloride,  arsenic, 
and,  generally,  lead  and  calcium  chlorides.  Its  yellow  color  is 
partly  due  to  organic  matter,  and  sometimes  to  iron  and  free  chlo- 
rine. To  remove  arsenic  and  sulphuric  acid,  the  acid  is  diluted  to 
1.12  sp.  gr.,  and  barium  sulphide  is  added ;  a  pure  hydrochloric  acid 
vapor  is  then  driven  out  by  distillation  and  absorbed  in  pure  water. 
Or  a  solution  of  stannous  chloride  in  concentrated  hydrochloric  acid 
is  added  to  the  crude  acid,  which  latter  must  have  a  strength  of  at  least 
1.15  sp.  gr.  A  brown  precipitate  of  arsenic  with  some  tin  separates 
and  is  removed  by  decantation.*  Sulphuric  acid  alone  is  removed 
by  adding  barium  chloride  and  redistilling.  To  remove  chlorine,  the 
crude  acid  is  digested  with  strips  of  copper  for  some  hours.  This 
precipitates  arsenic,  and  the  chlorine  combines  with  the  copper. 
The  acid  is  then  redistilled. 

Attempts  to  recover  hydrochloric  acid  from  the  waste  liquors  of 
the  ammonia  soda  process  (p.  86)  have  not  proved  very  successful. 
The  magnesium  chloride  mother-liquors  from  the  potash  salts  of 
Stassfurt  (p.  132)  may  be  decomposed  by  distillation  with  steam, 
and  a  dilute  hydrochloric  acid  obtained. 

MgCl2  +  H20  =  2  HC1  +  MgO. 

But  this  has  not  proved  a  commercial  success. 

The  Hargreaves  and  Robinson  process  for  the  direct  production 
of  hydrochloric  acid  and  sodium  sulphate  from  salt,  sulphur  diox- 
ide, water,  and  oxygen,  is  of  some  importance.  The  damp  salt  is 
pressed  into  blocks  and  dried ;  it  is  then  charged  into  vertical  cast- 
iron  retorts,  a  number  of  which  are  connected  in  a  series.  These 

*  3  SnCl2  -f  6  HC14-  As203  =  As2  +  3  H20  +  3  SnCl4. 

2  AsCl3  +  3  SnCl2  =  As2  +  3  SnCl4. 
This  leaves  stannic  chloride  in  the  acid. 


72  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

are  heated  from  without ;  the  temperature  of  the  reaction  is  from 
400°  to  550°  C.  The  sulphur  dioxide,  steam,  and  air  are  made  to 
pass  through  all  the  retorts  in  succession,  the  hydrochloric  acid 
being  carried  along  with  them.  A  slight  excess  of  sulphur  dioxide 
and  steam  is  used  to  prevent  the  mutual  reaction  between  the  hydro- 
chloric acid  vapor  and  the  oxygen,  by  which  chlorine  is  set  free. 
The  decomposition  being  slow,  the  gases  must  be  kept  in  contact 
with  the  salt  for  a  considerable  length  of  time ;  a  cylinder  contain- 
ing 40  tons  of  material  requiring  from  15  to  20  days'  continuous 
action  to  secure  complete  conversion. 

The  process  is  an  uninterrupted  one ;  for  as  soon  as  no  more  sul- 
phur dioxide  is  absorbed  in  a  given  cylinder,  it  is  cut  out  from  the 
series,  the  sodium  sulphate  removed,  a  new  charge  of  salt  blocks 
introduced,  and  the  cylinder  made  the  final  one  of  the  series ;  so 
that  newly  charged  salt  is  exposed  to  the  most  nearly  exhausted 
sulphur  fumes.  The  reaction  representing  the  process  appears  quite 
simple :  — 

2  NaCl  +  S02  +  H2O  +  O  =  Na2S04  +  2  HC1. 

But  the  mechanical  difficulties  encountered  in  working  it  were  very 
great,  and  only  within  a  very  short  time  has  the  process  met  with 
any  marked  success. 

Sodium  sulphate  or  salt-cake  is  most  largely  used  in  the  produc- 
tion of  soda  by  the  Leblanc  process.  Large  quantities  are  used  for 
glass  making,  for  ultramarine,  in  dyeing  and  coloring,  and  to  some 
extent  in  medicine.  For  some  kinds  of  glass  the  salt-cake  must  be 
free  from  iron,  and  consequently  it  is  made  in  lead  pans.  Or  the 
sulphate  may  be  purified  from  iron  and  excess  of  acid  by  dissolving 
it  in  hot  water,  adding  "  milk  of  lime,"  and  then  stirring  into  it  a 
solution  of  bleaching  powder.  The  iron  is  precipitated  as  hydroxide 
and  settles  on  standing.  By  evaporation,  crystals  of  Glauber's  salt 
(Na2S04  •  10  H20)  are  obtained.  But  generally  the  purified  solution 
is  rapidly  evaporated  to  dryness,  and  the  product  is  calcined  to 
remove  all  the  water. 

REFERENCES 

Berichte  iiber  die  Entwickelung  der  Chemischen  Industrie,  u.s.  w.  A.  W." 
Hofmann,  Braunschweig,  1877.  (Vieweg.) 

Darstellung  von  Chlor  und  Salzsaure,  unabhangig  von  der  Leblanc  Soda  Indus- 
trie. Dr.  N.  Caro,  Berlin,  1893.  (Oppenheim.) 

Sulphuric  Acid  and  Alkali.  2d  ed.  Vol.  II.  G.  Lunge,  London,  1895.  (Gur- 
ney  and  Jackson.) 


THE  SODA  INDUSTRIES  73 

THE   SODA  INDUSTRIES 

THE  LEBLANC  SODA  PROCESS 

Nearly  all  the  soda  of  trade  was  formerly  obtained  from  certain 
natural  deposits  of  the  so-called  "  sesquicarbonate,"  or  from  the  ashes 
of  sea  plants.  But  towards  the  end  of  the  last  century,  the  sup- 
ply from  these  sources  became  insufficient  to  meet  the  increasing 
demands.  About  1775  the  French  Academy  of  Science  offered  a 
large  prize  for  a  method  of  making  soda  from  salt.  Among  other 
processes  submitted  was  one  by  Nicolas  Leblanc,  which  seemed 
promising,  and  being  granted  a  patent  in  1791,  he  began  manufact- 
uring on  a  commercial  scale.  But  in  the  French  Eevolution  his 
factory  was  seized,  the  patent  declared  public  property,  and  no 
indemnity  was  paid  to  him.  Having  lost  all  his  property,  he 
finally  committed  suicide. 

Leblanc's  process  was  so  perfect  and  complete  that  very  slight 
changes,  and  those  only  in  minor  details,  have  been  made  up  to  the 
present.  It  has  been  in  use  now  for  nearly  a  century,  and  although 
very  seriously  threatened  by  newer  processes,  it  still  produces  about 
half  of  the  world's  supply  of  soda.  Owing  to  the  fact  that  it  pro- 
duces hydrochloric  acid  and  bleaching  powder  as  by-products,  it  has 
been  able  to  survive  competition,  although  its  condition  is  becom- 
ing more  desperate  every  year.  Its  chief  rival  is  the  ammonia  or 
Solvay  process.  Within  a  few  years  many  electrolytic  methods  for 
caustic  soda  have  appeared,  and  the  successful  production  of  bleach- 
ing material  by  any  of  these  processes  will  sweep  away  about  the 
only  source  of  profit  now  left  to  the  Leblanc  manufacturer.  It  is  not 
probable  that  this  change  will  come  immediately,  for  the  electrolytic 
processes  have  not  yet  entirely  emerged  from  the  experimental 
stage  ;  but  the  decline  of  the  Leblanc  process  is  generally  regarded 
as  inevitable,  and  inventors  have,  for  the  most  part,  abandoned 
further  attempts  to  improve  it. 

The  reactions  of  the  Leblanc  process  are  generally  expressed  as 
follows  :  — 


2)  Na2S04  +  2  C  =  Na2S  +  2  C02. 

3)  Na2S  +  CaC03  =  Na^COs  +  CaS. 
4) 


74 


OUTLINES  OF  INDUSTRIAL   CHEMISTRY 


But  these  equations  *  do  not  represent  all  the  reactions  which 
take  place  during  the  process,  for  a  number  of  other  substances  are 
formed.  The  first  equation  represents  the  preparation  of  sodium 
sulphate  and  hydrochloric  acid  (p.  67).  The  second  and  third  reac- 
tions are  realized  in  one  operation.  The  fourth  has  no  direct  rela- 
tion to  the  process,  as  the  formation  of  carbonic  oxide  does  not 
become  marked  until  all  the  salt-cake  has  been  decomposed.  This 
serves  to  indicate  the  end  of  the  process,  and  aids  in  the  formation 
of  a  porous  product. 

The  salt-cake  should  be  friable  and  porous,  containing  very  little 
free  sulphuric  acid,  and  no  undecomposed  chloride.  The  carbon 
is  supplied  in  the  form  of  powdered  coal,  which  should  contain  very 
little  ash-forming  impurity.  A  little  pyrite  does  no  harm,  but  the 
coal  should  be  as  free  as  possible  from  nitrogen,  in  order  to  prevent 
the  formation  of  cyanides  and  cyanates.  Calcium  carbonate  in  the 
form  of  pure  limestone  or  chalk,  crushed  to  the  size  of  a  small  pea, 
is  mixed  with  the  crushed  salt-cake  and  coal  in  order  to  carry  out 
the  third  reaction.  If  the  limestone  contains  magnesia  or  silica, 
there  is  a  consequent  loss  as  insoluble  residue.  Usually  100  pounds 
of  salt-cake,  100  pounds  of  limestone,  and  50  pounds  of  coal  dust 
form  a  charge.  This  is  an  excess  of  limestone,  the  purpose  of  which 
is  explained  below. 

The  reactions  are  carried  out  in  a  "  black-ash  "  or  "  balling  fur- 
nace/7 which  may  be  worked  either  by  hand  or  mechanically.  The 


^J  L2^$^ 


FIG.  38. 


hand-worked  furnace  is  a  long  reverberatory  (Fig.  38),  having  two 
platforms  on  the  hearth.  The  charge  is  introduced  on  the  back  plat- 
form (A)  nearest  the  flue,  where  the  heat  is  not  very  high.  When 
thoroughly  dried  and  well  heated,  it  is  raked  down  onto  the  front 
platform  (B),  which  is  a  few  inches  lower  than  (A).  Here  the  tem- 

*  Lunge  (Sulph.  Acid  and  Alkali,  Vol.  II,  460  et  seq.)  regards  the  theory  of 
Scheurer-Kestner  (Comptes  rendus,  57,  1013,  and  58,  501)  as  correct,  viz.  that  the 
reactions  are :  — 

5  Na2SO4  +  10  C  =  5  Na2S  + 10  CO2. 

5  Na2S  +  5  CaCOg  =  5  Na2CO3  +  5  CaS. 

2  CaCO3  +  2C  =  2  CaO  +  4  CO. 


THE   SODA   INDUSTRIES 


75 


perature  is  high,  usually  about  1000°  C.,  and  the  surface  of  the  mass 
soon  begins  to  fuse.  It  is  then  raked  over,  thoroughly  exposing  it 
to  the  direct  heat  until  it  becomes  a  thick,  pasty  mass,  from  which 
carbon  dioxide  is  escaping  freely.  After  the  salt-cake  is  all  decom- 
posed, the  charge  begins  to  stiffen,  and  the  evolution  of  carbon 
monoxide  is  shown  by  the  appearance  of  jets  of  blue  flame,  known 
to  the  workmen  as  "  candles."  The  charge  is  then  raked  together 
into  a  "  ball,"  which  is  drawn  out  of  the  furnace  into  an  iron  barrow. 
The  evolution  of  carbon  monoxide  continues  for  a  few  minutes  after 
the  "  ball "  is  removed,  and  the  bubbles  escaping  from  the  pasty  mass 
cause  it  to  become  porous.  The  formation  of  this  gas  is  due  to  the 
action  between  the  coal  and  the  excess  of  limestone  according  to 
reaction  (4).  The  caustic  lime  formed  here  slakes  during  the  lixi- 
viation  of  the  black-ash  (p.  76),  and  swells,  thus  disintegrating  the 
mass. 

Although  the  heavy  tools  are  suspended  by  chains,  their  opera- 
tion is  still  so  difficult,  and  the  temperature  is  so  high,  that  a  man 
cannot  handle  much  more  than  300  pounds  at  one  time.  In  order 
to  work  larger  charges,  without  the  expensive  hand  labor,  revolving 


FIG.  8». 

black-ash  furnaces  (Fig.  39)  are  much  used.  These  are  similar  to 
the  revolving  furnaces  described  on  page  17;  the  flame  from  the 
furnace  (A)  passes  through  the  cylinder  (B).  The  charge  is  intro- 
duced through  the  manhole  (P),  and  the  finished  product  discharged 
through  the  same  opening,  into  the  wagon,  at  the  end  of  the  opera- 
tion. The  cylinder  is  about  16  feet  long  by  10  feet  in  diameter,  and 
is  revolved  by  a  gear  (E)  connected  with  an  engine.  Projections 
are  fixed  in  the  lining  to  help  mix  the  contents.  The  charge  is  usu- 
ally about  two  tons  of  salt-cake,  with  proportionate  amounts  of  coal 
and  limestone.  It  is  customary  to  introduce  only  the  limestone  and 
a  part  of  the  coal  at  first,  and  to  rotate  the  cylinder  until  some 
caustic  lime  is  formed;  then  the  remainder  of  the  coal,  together 
with  the  salt-cake,  is  introduced,  and  the  rotation  continued  until 
the  reactions  are  completed.  The  speed  varies  from  one  revolution 


76  OUTLINES  OF  INDUSTRIAL   CHEMISTRY 

in  three  or  four  minutes,  at  first,  to  four  or  five  revolutions  per 
minute  during  the  last  part  of  the  process. 

The  hot  gases  from  the  black-ash  furnace,  whether  hand-worked 
or  mechanical,  pass  through  the  dust  box  (N),  and  then  through  the 
long  flue  over  the  pan  (J,  J)  on  their  way  to  the  chimney  (D).  In 
this  shallow  pan,  the  liquor  obtained  by  lixiviating  the  black-ash  is 
evaporatecj.  When  crystallized,  the  salts  are  removed  through  the 
small  doors  (J). 

Black-ash  is  a  brownish  black  or  dark  gray  substance  of  a 
pumice-like  texture,  containing  about  45  per  cent  sodium  carbonate, 
30  per  cent  calcium  sulphide,  10  per  cent  caustic  lime,  and  from  10 
to  12  per  cent  of  other  impurities,  —  sulphate,  silicate,  aluminate, 
and  chloride  of  sodium,  calcium  carbonate,  coal,  and  iron  oxide,  with 
traces  of  cyanides  and  of  sulphides  of  sodium. 

The  next  stage  in  the  process  is  the  lixiviation  of  the  black-ash. 
This  presents  some  difficulties :  if  the  black-ash  is  put  directly  into 
cold  water,  it  often  agglomerates  in  hard  lumps,  which  dissolve 
exceedingly  slowly ;  the  free  lime  present  forms  calcium  hydroxide, 
which  reacts  with  the  sodium  carbonate  solution,  forming  some 
caustic  soda ;  the  solution  of  sodium  carbonate,  especially  if  hot  and 
dilute,  reacts  on  any  calcium  sulphide  present,  forming  some  sodium 
sulphide ;  moreover,  moist  calcium  sulphide  oxidizes  rapidly  to  sul- 
phate in  the  air,  and  this  reacts  with  the  sodium  carbonate.  Hence 
the  lixiviation  must  be  done  as  rapidly  as  possible,  at  a  low  tem- 
perature, and  without  exposing  the  wet  black-ash  to  the  air. 

Shank's  process  gives  the  most  satisfactory  results.  The  lixivia- 
tion is  carried  on  in  a  series  of  tanks,  each  having  a  false  bottom 
perforated  with  small  holes.  Because  of  its  density,  the  solution 
of  sodium  carbonate  sinks,  and  passing  through  these  perforations, 
is  drawn  off  by  means  of  a  pipe  which  delivers  it  at  the  top  of  the 
next  tank.  There  must  always  be  sufficient  liquor  in  each  tank  .to 
keep  the  black-ash  entirely  submerged.  The  process  is  continuous, 
sufficient  fresh  water  being  admitted  to  the  nearly  exhausted  ash  to 
give  an  unbroken  flow  of  strong  liquor  (above  45°  Tw.)  from  the 
last  tank  of  the  series.  When  the  liquor  from  the  last  tank  falls 
to  45°  Tw.,  it  is  turned  into  a  tank  which  has  just  been  filled  with 
new  ash.  The  exhausted  ash  is  washed  until  the  wash  water  has 
a  density  of  only  1°  Tw.  Then  the  residue  of  calcium  sulphide  and 
hydroxide,  coal,  ashes,  and  other  insoluble  matter,  which  constitutes 
the  "tank  waste,"  is  sent  to  the  dump.  The  tank  is  then  refilled 
with  black-ash  and  made  the  last  of  the  series,  to  receive  the  strong 
liquors  from  the  preceding  tank. 


THE   SODA   INDUSTRIES  77 

Since  the  black-ash  contains  caustic  lime,  sufficient  heat  is  gen- 
erated by  its  slaking  during  the  lixiviation  to  warm  the  concen- 
trated liquor  to  about  50°  C.,  which  is  the  best  temperature  for 
complete  extraction.  The  temperature  of  the  dilute  lye  from  the 
first  tank  of  the  series  is  not  allowed  to  rise  above  38°  C.,  in  order 
to  prevent  the  above-mentioned  interaction  between  the  calcium  sul- 
phide and  the  sodium  carbonate. 

Good  tank  liquor  has  approximately  the  following  composition :  — 

Na2CO3  (+NaOH) 23.60* 

NaCl 50 

Na-jS 13 

Na2S2O3 30 

Na2S04 '    .     .     .       .23 

NaoSi03 

NaCN 

NaCNS 

FeS  (in  solution) 

The  lye  obtained  by  the  lixiviation  has  a  specific  gravity  of  about 
1.25,  and  is  muddy  from  suspended  impurities.  It  is  purified  by 
settling  and  then  pumped  to  the  top  of  the  "  carbonating  towers," 
which  are  filled  with  pebbles  or  coke,  or  have  numerous  chains  or 
wire  ropes  suspended  from  the  top  and  weighted  at  the  lower  ends. 
The  tank  liquor  trickles  over  the  porous  material  or  chains,  and 
comes  into  intimate  contact  with  a  strong  current  of  carbon  dioxide  f 
entering  at  the  bottom  and  passing  up  through  the  tower. 

The  carbon  dioxide  and  oxygen  which  pass  through  the  tower, 
convert  the  caustic  soda  to  carbonate,  decompose  the  ferro-sodium 
sulphide  (solution  of  ferrous  sulphide  in  sodium  sulphide),  convert- 
ing the  sodium  sulphide  into  bicarbonate,  and  precipitating  the  iron, 
together  with  any  silica  and  alumina  which  may  be  present. 

The  reactions  involved  were  supposed  to  be  the  following :  — 

1)  2  NaOH  +  C02  =  Na2C03  +  H2O. 

2)  Na2S  -f  C02  +  H20  =  NaHC03  +  NaSH. 

3)  NaHC03  +  NaSH  =  Na2C03  +  H2S. 

But  Lunge  has  shown  that  reactions  (2)  and  (3)  may  not  be  fully 
realized,  and  hence  that  the  decomposition  of  sodium  sulphide  is 

*  Mohr,  Analysis  of  Soda-ash  from  Stolberg  (Lunge,  Sulphuric  Acid  and  Alkali, 
Vol.11). 

t  This  is  derived  from  the  gases  of  the  black-ash  furnace,  which  also  contain 
some  oxygen.  Or  it  is  obtained  from  the  gases  from  lime  kilns,  which  are  much 
richer  in  carbon  dioxide  and  introduce  less  flue  dust  into  the  product. 


78  OUTLINES  OF   INDUSTRIAL   CHEMISTRY 

very  difficult.  Some  manufacturers  complete  the  purification  of  the 
tank  liquor  by  adding  zinc  hydroxide,  which  precipitates  the  sul- 
phide :  — 

Na2S  -f  Zn  (OH)2  -  ZnS  +  2  NaOH. 

If  air  is  blown  through  the  tank  liquor,  the  sodium  sulphide  is  con- 
verted into  thiosulphate :  — 

Na2S  +  2  02  +  H20  =  2  NaOH  +  Na2S  A- 

The  tank  liquor  may  be  better  purified  according  to  Fault's 
process,  in  which  a  little  "  Weldon  mud  "  is  added  to  the  liquor,  and 
air  and  steam  blown  through  it.  This  oxidizes  the  sodium  sulphide 
very  completely,  besides  precipitating  ferric  oxide,  silica,  and  alumina 
in  the  sludge.  If  the  "Weldon  mud"  be  regarded  as  manganese 
dioxide,  for  brevity  the  reactions  may  be  written  as  follows :  — 

2  Na2S  +  4  Mn02  +  5  H20  =  2  NaOH  +  Na2S  A  4-  Mn  (OH)* 
4  Mn  (OH),  +  2  02  =  4  Mn02  +  4  H20. 

Since  nearly  all  the  manganese  oxide  is  thus  recovered,  it  may  be 
used  repeatedly,  until  it  becomes  very  much  contaminated  with 
ferric  oxide,  silica,  alumina,  etc. 

After  settling,  the  purified  and  carbonated  tank  liquor  is  drawn 
directly  into  the  evaporating  pans,  which  are  usually  large  shallow 
iron  tanks,  the  liquor  being  heated  by  surface  contact  with  the 
waste  gases  from  the  black-ash  furnace.  Sometimes  deep  pans, 
heated  from  below,  are  used,  since  surface  evaporation  gives  a 
product  contaminated  with  dust  from  the  furnace.  The  liquor  is 
evaporated  directly  to  dryness,  and  the  "  black  salt "  (chiefly  mono- 
hydrated  sodium  carbonate,  Na2C03  •  H20)  is  calcined  by  heating  it 
to  a  red  heat.  Sometimes  sawdust  is  mixed  with  the  uncarbonated 
liquor  before  evaporation,  and  then  on  calcining,  the  soda-ash  is 
carbonated  by  the  carbonaceous  matter  from  the  wood;  but  the 
charge  is  very  liable  to  cake  in  this  operation.  The  caustic  soda 
and  sodium  sulphide  of  the  tank  liquor  are  thus  converted  to  sodium 
carbonate,  and,  after  all  the  sawdust  is  burned  out,  the  ash  becomes 
white  or  light  brown. 

Or  the  liquor  is  evaporated  till  a  crystalline  mass  separates ; 
then  the  mother-liquor  ("red  liquor")  is  drawn  off,  and  the  black 
salt  is  raked  out  of  the  pan.  Much  care  is  necessary  to  prevent  the 
formation  of  a  crust  or  the  burning  on  of  the  precipitated  carbonate. 

In  most  large  works,  a  semicircular  evaporating  pan  is  used, 
provided  with  mechanical  scrapers,  to  prevent  the  black  salt  from 
adhering  to  the  pan.  The  best  form  of  this  apparatus  is  Thelen's 


THE   SODA   INDUSTRIES 


79 


pan  (Fig.  40).     In  this,  the  scrapers  (R,  R)  move  the  salts  towards 
the  end  of  the  pan  as  they  deposit,  and  a  scoop  lifts  them  to  the 


draining  apron.     The  beam  (B)  carrying  the  frame  from  which  the 
scrapers  are  suspended,  is  rotated  by  the  gear  (J). 

For  a  very  light  colored  product,  the  crude  soda-ash  is  dissolved 
in  water,  and  a  little  bleaching  powder  solution  added;  the  pre- 
cipitated iron  and  other  impurities  settle  out,  and  the  clear  solu- 
tion is  evaporated  until  a  thick  mass  of  crystals  separates,  when  the 
mother-liquor  is  drawn  off  to  remove  any  soluble  impurities.  The 
monohydrated  salt  remaining  is  then'  calcined  without  the  addition 
of  carbonaceous  matter,  to  remove  its  crystal  water,  and  the  product 
is  called  "white  alkali"  or  "refined  alkali."  A  little  sodium  chlo- 
ride is  formed  by  the  addition  of  the  bleaching  powder,  so  that 
refined  alkali  is  not  quite  so  strong  as  soda-ash.  It  is  chiefly  used 
for  glass  making  and  other  purposes  where  iron  and  sulphides 
would*  be  detrimental.  Good  Leblanc  soda  is  nearly  white  or  pale 
yellow,  and  should  contain  but  few  black  specks.  It  usually  con- 
tains a  little  caustic  soda,  a  trace  of  sulphides  and  sulphites,  some 
chloride  and  sulphate,  and  not  over  1  per  cent  of  insoluble  matter. 
It  should  be  finely  ground  before  packing. 

Soda  crystals  or  sal-soda  CN"a2C03  •  10  H20)  is  made  by  dissolving 
soda-ash  in  warm  water,  allowing  the  hot  solution  to  stand  quietly 
until  all  sediment  deposits,  and  drawing  off  the  clarified  liquor  into 
crystallizing  tanks,  where  it  is  cooled  to  the  atmospheric  tempera- 
ture. Large  crystals  of  sal-soda,  very  nearly  pure,  are  deposited. 
They  contain  over  60  per  cent  of  water,  and  are  thus  very  bulky 
and  not  economical  to  ship ;  but  they  are  still  preferred  to  soda-ash 
by  some  manufacturers.  They  do  not  dissolve  so  readily  as  soda- 
ash.  They  are  sometimes  used  for  making  sodium  bicarbonate,  by 
exposing  them  on  a  grating  to  an  atmosphere  of  carbon  dioxide :  — 

10  H20  +  C02  =  2  NaHC03  +  9  H20. 


80  OUTLINES  OF  INDUSTRIAL   CHEMISTRY 

The  water  resulting  from  the  reaction  drips  through,  leaving  the 
bicarbonate  on  the  grating. 


CAUSTIC  SODA 

Caustic  soda  is  made  from  soda-ash,  or  from  the  "  tank  liquors  " 
directly,  by  adding  calcium  hydroxide  (milk  of  lime)  to  the  solu- 
tion :  — 

Na2C03  +  Ca(OH)2  =  CaCO3  +  2  NaOH. 

When  caustic  soda  is  the  ultimate  product,  it  is  generally  custom- 
ary to  use  this  lime  mud  (CaC03)  instead  of  limestone,  in  the 
charge  for  the  black-ash  furnace,  for  the  formation  of  caustic  in 
the  tank  liquor  is  then  of  course  not  objectionable. 

The  tank  liquor  must  not  have  a  density  of  over  20°  Tw.  (1.10 
sp.  gr.),  or  it  will  attack  the  calcium  carbonate  formed,  and  cause 
a  partial  reversion  of  the  reaction.  Consequently  it  is  diluted  with 
the  wash  waters  from  the  lime  mud  of  a  previous  operation.  The 
liquor  is  then  heated  to  boiling,  and  run  into  large  iron  tanks,  where 
the  "  milk  of  lime  "  is  added,  and  the  mixture  well  stirred.  Air  or 
steam  is  usually  blown  into  the  liquor  to  assist  in  the  mixing.  The 
air,  especially  when  aided  by  the  addition  of  "  Weldon  mud"  (p.  97), 
converts  the  sodium  sulphide  to  sodium  thiosulphate  and  sulphate :  — 

2  Na2S  +  H2O  +  40  =  2  NaOH  +  Na2S203. 

The  thiosulphate  is  afterwards  destroyed  by  oxidizing  it  to  the 
sulphate. 

The  solution  of  caustic  soda  is  allowed  to  settle  and  is  drawn 
into  cast-iron  kettles,  which  are  heated  by  direct  fire  until  the  water 
is  evaporated  and  the  caustic  soda  remains  as  a  fused  mass.  Some 
nitre  is  then  added,  or  air  is  blown  in  to  complete  the  oxidation  of 
any  thiosulphate  to  normal  sulphate,  which  remains  in  the  caustic, 
reducing  its  strength.  To  make  very  strong  caustic,  zinc  oxide  is 
often  used  to  remove  the  sulphide  from  the  tank  liquors :  — 

Na^S  -f  ZnO  +  H2O  =  2  NaOH  +  ZnS. 

The  precipitated  zinc  sulphide  is  settled  out,  before  evaporating 
the  caustic  liquor.  By  calcining  the  zinc  sulphide,  the  zinc  is  re- 
converted to  oxide. 

Sometimes  the  Yaryan  system  (p.  6)  is  used  to  evaporate  the 
dilute  caustic  soda  solution  till  it  reaches  a  density  of  60°  Tw.,  at 
which  point  the  other  salts,  such  as  sodium  carbonate,  which  are 
dissolved  in  the  caustic  liquor,  begin  to  crystallize;  the  liquor  is 


THE  SODA  INDUSTRIES  81 

then  transferred  to  the  open  pan  and  the  evaporation  continued,  the 
salts  being  raked  out  as  they  separate. 

The  fused  caustic  soda  is  run  directly  into  the  sheet-iron  drums 
in  which  it  is  sold.  These  are  sealed  as  soon  as  cold,  to  prevent 
the  absorption  of  moisture  by  the  caustic. 

Loewig's  process  *  for  caustic  soda  depends  on  the  formation 
of  sodium  ferrate  (Na2Fe204),  which  is  then  decomposed  with  water. 
The  soda  liquors  are  mixed  with  ferric  oxide,  and  the  mass  evapo- 
rated to  dryness  and  calcined  at  a  bright  red  heat,  usually  in  a 
revolving  furnace.  By  the  calcination,  a  reaction  between  the 
sodium  carbonate  and  the  iron  oxide  is  brought  about,  carbon  dioxide 
escaping  and  sodium  ferrate  remaining  in  the  furnace.  The  mass 
is  washed  with  cold  water  until  all  soluble  matter  is  removed ;  then 
water  at  90°  C.  is  run  over  the  sodium  ferrate,  by  which  it  is  de- 
composed, caustic  soda  formed,  and  iron  oxide  regenerated;  the 
last  is  returned  to  the  calcining  process.  The  ferric  oxide  used  is 
a  natural  iron  ore,  very  clean  and  free  from  silica  or  other  impurities ; 
that  made  by  calcining  a  precipitated  ferric  hydroxide  is  not  well 
adapted  to  the  process,  as  it  gives  a  product  difficult  to  lixiviate. 
The  density  of  the  resulting  solution  of  caustic  is  about  62°  Tw. 
(1.31  sp.  gr.),  and  so  less  evaporation  is  necessary  than  in  the  lime 
process,  where  the  density  is  only  15°  or  20°  Tw.  Moreover,  there 
are  no  other  salts  present,  such  as  sulphate,  thiosulphate,  sulphide, 
or  chloride,  and  the  product  is  purer  than  that  yielded  by  the  lime 
process.  But  Loewig's  process  is  not  so  well  adapted  to  use  with 
the  Leblanc  soda-ash,  because  the  tank  liquors  must  be  evaporated 
to  dryness  before  calcining  the  ferric  oxide  and  sodium  carbonate 
mixture,  and  the  sodium  carbonate  must  be  quite  pure.  The  pro- 
cess may  be  advantageously  used  with  ammonia  soda-ash,  since  this 
is  obtained  directly  as  a  solid  and  no  evaporation  is  necessary. 

Caustic  soda  of  better  quality  can  be  made  by  Loewig's  method, 
but  it  cannot  be  made  so  cheaply  as  by  the  use  of  lime  with  the 
tank  liquor  of  the  Leblanc  process,  especially  in  small  works  where 
the  output  is  irregular  and  uncertain.  For  although  there  is  no 
expense  for  lime,  and  less  fuel  is  used  for  evaporation  in  the  former 
method,  yet  an  extensive  and  somewhat  costly  plant,  designed  to 
reduce  labor  to  the  minimum,  is  required,  and  considerable  fuel  is 
needed  for  the  calcination. 

For  the  preparation  of  caustic  soda  by  electrolysis  of  brine,  see 
p%  104. 

*  German  Patent,  No.  1650,  Dec.  21,  1877.  J.  Soc.  Chem.  Ind.,  1887,  438. 
Konrad  W.  Jurisch,  Die  Fabrikation  von  Schwefelsaurer  Thonerde,  p.  13. 


82 


OUTLINES  OF  INDUSTRIAL  CHEMISTRY 


TREATMENT   OP  TANK   WASTE 

In  the  Leblanc  process  nearly  all  the  sulphur  of  the  salt-cake 
remains  in  the  "  tank  waste  "  or  residue  from  the  lixiviation  of  the 
black-ash.  The  average  composition  of  this  waste  is  shown  in  the 
following  tables :  — 

COMPOSITION  OF  TANK  WASTE 
FRESH  * 


EEVOLVEE 

HAND  FUBNACE 

HAND  FUENACB 

Water  

29.20 

29.96 

30.40 

Na2C08     .     . 

3.16 

1.97 

1.63 

CaCOs       

21.19 

36  92 

38  81 

Ca(OH)2  .... 

Trace 

8  85 

9  53 

CaS.     . 

56  89 

37  90 

35  12 

CaSgOs 

1  07 

0  68 

1  49 

CaS03  

Trace 

CaSO4  

Trace 

0.20 

CaSi08  

3  53 

1.34 

1  21 

Coal     . 

7.20 

7.04 

6  27 

ALOi 

1  02 

0  37 

0  13 

FeS 

1  65 

2  44 

2  76 

Sand    

2.82 

1.79 

2.61 

COMPOSITION  OF  WEATHERED  TANK  WASTE 
60  YEARS  OLD  t 


19  INCHES  BELOW  THE 
SFRFACB 

5  FEET  BELOW  THB 
SURFACE 

CaCO3 

53  14 

52  77 

CaS04    

17.87 

11.11 

CaS03    

0.65 

3.10 

CaS208   

0.80 

2.89 

CaS    ... 

0.04 

Insoluble  in  HC1 

10.10 

10.91 

A^Os  Fe20s  etc                    .     . 

7.18 

11.04 

Water    

10.26 

8.14 

*  Chance,  J.  Soc.  Chem.  Ind.,  1882,  p.  266. 

f  Lunge,  Sulphuric  Acid  and  Alkali,  2d  ed.,  Vol.  II,  p.  815. 


THE   SODA  INDUSTRIES  83 

When  fresh  waste  is  thrown  on  the  dump,  the  changes  produced 
by  weathering  cause  great  nuisance.  The  air  is  contaminated  by 
the  hydrogen  sulphide  and  sulphur  dioxide  liberated,  and  the  soluble 
polysulphides  of  calcium  and  sodium  formed  are  dissolved  by  rain- 
water making  the  objectionable  "yellow  liquors/'  which  run  into 
streams  and  sewers. 

In  fresh  waste  the  sulphur  is  chiefly  in  the  form  of  sulphide  and 
thiosulphate  of  calcium,  but  in  weathered  material  these  have  been 
converted  by  oxidation  into  sulphate  and  sulphite,  which  in  them- 
selves cause  no  trouble  except  by  their  bulk. 

The  simplest  method  of  disposing  of  waste  is  to  send  it  out  to 
sea  and  dump  it,  if  the  works  are  so  situated  that  this  is  convenient ; 
or,  if  this  is  impossible,  to  spread  it  evenly  and  beat  it  down  hard  to 
prevent  as  far  as  possible  the  infiltration  of  rain.  But  since  the  sul- 
phur thus  lost  every  year  represents  an  enormous  money  value, 
many  attempts  have  been  made  to  recover  it  in  an  available  form. 
Of  the  numerous  processes  proposed  only  three  need  be  considered 
here. 

In  Mond's  process  the  waste  was  treated  directly  in  the  lixiviat- 
ing tanks  by  blowing  air  or  chimney  gases  through  the  wet  mass. 
This  oxidized  the  waste  according  to  the  following  reactions:  — 

1)  2  CaS  +  2  H20  =  Ca(SH)2  +  Ca(OH)2. 

2)  Ca(SH)2  +  40  =  CaS203  +  H20. 

But  the  hydration  and  oxidation  processes  were  slow,  and  after  a 
time  it  was  necessary  to  lixiviate  the  mass,  blow  in  air,  and  again 
lixiviate.  By  several  lixiviations  the  calcium  sulphydrate  and  thio- 
sulphate were  dissolved,  forming  "  yellow  liquors."  To  recover  the 
sulphur  these  were  treated  while  still  hot  with  dilute  hydrochloric 
acid,  the  following  reactions  *  taking  place :  — 

3)  CaS203  +  2  HC1  =  CaCl2  +  H20  +  S02  +  S. 

4)  Ca(SH)2  +  2  HC1  =  Ca012  +  2  H2S. 

In  the  presence  of  the  calcium  chloride  solution  the  two  gases, 
sulphur  dioxide  and  hydrogen  sulphide,  react  upon  each  other,  form- 
ing water  and  free  sulphur :  — 

5)  2H2S  +  S02  =  2H20  +  3S. 

The  hydration  and  oxidation  process  was  so  controlled  that  the 
proportion  of  thiosulphate  to  sulphydrate  yielded  one  molecule  of 

*  Mactear  proposed  to  use  the  same  reactions  for  the  treatment  of  the  drainage 
from  old  waste  heaps,  which  were  creating  a  nuisance. 


84  OUTLINES  OF   INDUSTRIAL   CHEMISTRY 

sulphur  dioxide  to  two  molecules  of  hydrogen  sulphide.  When 
properly  worked  very  little  escape  of  hydrogen  sulphide  occurred. 
The  precipitated  sulphur  was  filtered  from  the  solution  of  calcium 
chloride  which  went  to  waste.  The  sulphur  was  then  refined. 

This  process  recovered  about  60  per  cent  of  the  total  sulphur,  but 
it  consumed  a  great  deal  of  hydrochloric  acid,  which  now  has  con- 
siderable value,  and  some  sulphur  was  lost  owing  to  the  formation 
of  sulphate  and  sulphite  of  calcium,  which,  being  insoluble,  were  left 
in  the  residue  after  lixiviation.  The  process  is  not  now  in  use. 

Shaffner  and  Helbig's*  process  depends  upon  the  reaction  be- 
tween magnesium  chloride  and  calcium  sulphide  in  a  boiling  solu- 
tion :  — 

1)  CaS  +  MgCl2  +  H20  =  CaCl2  +  MgO  +  H2S. 

2)  MgO  +  CaCl2  +  C02  =  CaC03  -f  MgCl2. 

The  second  reaction  was  employed  to  recover  the  magnesium  chloride, 
but  the  calcium  carbonate  formed  was  too  impure  for  use  in  the 
black-ash  furnace.  The  hydrogen  sulphide  set  free  was  pure,  and 
could  be  utilized  by  burning  it  with  air,  and  conveying  the  resulting 
sulphur  dioxide  into  the  lead  chambers  of  the  sulphuric  acid  plant  ; 
or  the  sulphide  could  be  decomposed  with  sulphur  dioxide,  accord- 
ing to  the  method  given  on  p.  83,  reaction  (5).  Lime-kiln  gases 
were  used  for  the  carbon  dioxide  in  reaction  (2).  This  process  was 
not  a  commercial  success. 

The  Chance-Claus  process  t  appears  to  be  the  only  successful 
method  of  recovering  sulphur  on  a  large  scale,  and  even  this  has  not 
fully  realized  the  original  expectations  of  its  promoters.  The  reac- 
tions of  the  process  were  proposed  by  Gossage  in  1837,  but  although 
he  worked  on  the  idea  for  thirty  years,  and  spent  a  large  fortune  in 
experimenting,  he  failed  to  make  it  a  success. 

The  following  are  the  reactions  involved  :  — 


2) 

3)   CaS  +  H2S  =  Ca(SH)2. 

A  pure  carbon  dioxide  containing  at  least  30  per  cent  C02  is  neces- 
sary ;  this  can  only  be  cheaply  obtained  in  a  carefully  regulated 
special  form  of  lime  kiln.  The  tank  waste  is  diluted  with  water  and 
put  into  one  of  a  series  of  seven  cast-iron  cylinders,  so  arranged  that 
one  may  be  emptied  and  recharged,  while  the  others  are  in  uninter- 
rupted operation.  The  freshly  filled  cylinder  is  made  the  last  of  the 

*  J.  Soc.  Chem.  Ind.,  1882,  264.  f  J.  Soc.  Chem.  Ind.,  1888,  162. 


THE  SODA   INDUSTRIES 


85 


series,  while  the  concentrated  carbon  dioxide  from  the  lime  kilns 
enter  the  cylinder  containing  the  most  nearly  decomposed  "  waste." 
The  hydrogen  sulphide  liberated  is  made  to  pass  into  the  succeeding 
cylinders,  where  it  reacts  with  the  calcium  sulphide  to  form  calcium 
sulphydrate,  according  to  reaction  (3).  This  sulphydrate  is  then 
decomposed  by  the  carbon  dioxide,  according  to  reaction  (2).  During 
the  formation  of  the  sulphydrate,  very  little  else  than  nitrogen 
escapes  from  the  last  cylinder  ;  but  when  the  decomposition  of  the 
sulphydrate  by  the  carbon  dioxide  begins  in  the  last  two  or  three 
cylinders,  hydrogen  sulphide  begins  to  escape  from  the  apparatus  ; 
when  this  gas  is  30  per  cent  H2S,  it  is  collected  in  a  gasometer; 
when  below  30  per  cent,  it  is  turned  into  the  most  recently  filled 
cylinder,  where  reaction  (3)  takes  place. 

The  hydrogen  sulphide  collected  in  the  gasometer,  together  with 
air,  is  passed  through  the  Glaus  sulphur  kiln  (Fig.  41),  in  which  the 
reaction 


takes  place.     On  the  grate  (A)  is  a  layer  of  broken  fire-brick  covered 
with  about  12  inches  of  ferric  oxide.     The  mixture  of  hydrogen  sul- 


H2SK> 


FIG.  41. 


phide  and  air  is  led  into  the  kiln  at  (B),  and  made  to  pass  through 
the  ferric  oxide  (previously  heated  to  a  dull  red)  ;  this  causes  the 
reaction  to  take  place,  and  at  the  same  time,  the  heat  generated  by 
the  reaction  is  sufficient  to  keep  the  iron  oxide  at  the  proper  tem- 
perature, after  being  once  well  started.  Sulphur,  nitrogen,  and  water 
vapor  escape  from  the  kiln.  The  sulphur  vapor  condenses  in  the 
chamber  (D)  as  liquid  sulphur,  and  in  (E)  as  flowers  of  sulphur, 
while  the  steam  and  nitrogen,  together  with  a  small  quantity  of  sul- 
phur dioxide,  pass  on  to  a  condensing  tower,  where  they  are  brought 
into  contact  with  water,  to  retain  the  last  traces  of  sulphur  dioxide. 
When  working  well,  this  process  recovers  about  85  per  cent  of  the 
sulphur.  According  to  Lunge,  the  form  of  the  kiln  has  been  recently 


86  OUTLINES  OF  INDUSTRIAL   CHEMISTRY 

modified,  but  the  principle  of  the  process  is  unchanged.  The  water 
in  the  storage  gasometer  is  usually  covered  with  a  layer  of  petroleum 
oil,  to  prevent  the  absorption  of  the  hydrogen  sulphide  by  the  water. 

The  process  is  not  very  lucrative  at  present,  owing  to  the  low 
price  of  sulphur,  but  since  it  reduces  the  nuisance  created  by  the 
alkali  waste,  a  number  of  English  firms  employ  it.  In  1893,  over 
30  plants  were  in  operation  in  England,  and  more  than  35,000  tons 
of  sulphur  recovered. 

For  the  Parnell  and  Simpson  *  process  for  utilizing  alkali  waste, 
see  p.  90. 

THE   AMMONIA   SODA   PROCESS 

The  reactions  involved  in  the  ammonia  soda  process  were  dis- 
covered by  H.  G.  Dyar  and  J.  Hemming,  about  1838,  but  owing  to 
the  mechanical  difficulties,  its  practical  success  was  not  thoroughly 
established  until  1873.  In  1863,  Ernest  Solvay,  a  Belgian,  con- 
structed an  apparatus  which  has  led  to  an  enormous  development  of 
the  industry,  by  which  one-half  of  the  world's  supply  of  soda  is  now 
made.  Its  advantages  lie  in  the  strength  and  purity  of  its  products 
and  the  absence  of  troublesome  by-products,  such  as  "  tank  waste." 
But  it  does  not  yield  chlorine  nor  hydrochloric  acid,  all  the  former 
going  to  waste  as  calcium  chloride. 

The  ammonia  soda  process  depends  upon  the  fact  that  sodium 
bicarbonate  is  but  slightly  soluble  in  a  cold  ammoniacal  solution  of 
common  salt.  The  technical  success  of  the  process  depends  chiefly 
on  the  proper  regulation  of  the  temperature  during  the  precipitation, 
and  on  the  capacity  of  the  works  to  handle  large  quantities  of  gases 
and  liquids.  As  far  as  possible,  manual  labor  must  be  avoided,  and 
the  products  moved  and  treated  in  solution  or  in  suspension.  The 
reactions  are  as  follows  :  — 


1)  Nad  +  NH3  +  H20  +  C02  =  NH4C1  +  NaHC03. 

2)  2  NH4C1  +  Ca(OH)2  =  CaCl2  +  2  H20  +  2  NH3. 

The  first  equation  is  the  chief  one  ;  the  second  represents  the  recov- 
ery of  the  ammonia,  and  is  essential  to  the  commercial  success  of 
the  process. 

The  salt  is  used  as  a  very  concentrated  brine,  which  has  been 
purified  from  iron,  silica,  magnesia,  etc.  ;  it  is  then  saturated  with 
ammonia  gas,  obtained  from  gas  liquors,  or  by  the  recovery  process 
according  to  equation  (2).  The  carbon  dioxide  is  obtained  partly 
from  lime  kilns  and  partly  from  the  calcination  of  the  bicarbonate 
*  J.  Soc.  Chem.  Ind.,  1889,  11. 


THE   SODA   INDUSTRIES 


87 


to  form  the  normal  carbonate  (p.  89).  It  must  contain  at  least 
30  per  cent  of  C02,  and  is  prepared  in  special  forms  of  continuous 
limekilns.  The  lime  resulting  is  used  in  the  recovery  of  the 
ammonia  (reaction  2),  and  for  making  caustic  soda;  the  limekiln 
gases  are  cooled,  and  the  sulphur  dioxide  removed,  by  washing  in 
water  before  they  pass  into  the  carbonating  towers.  (See  below.) 

The  brine  is  contained  in  a  tank,  under  the  perforated  bottom  of 
which  the  ammonia  gas  is  introduced,  and  rising  through  the  liquor, 
is  rapidly  absorbed.  The 
heat  evolved  by  the  absorp- 
tion is  taken  up  by  cold 
water  circulating  in  coils. 
When  saturated,  the  am- 
moniacal  brine  is  pumped 
into  a  receiving  and  settling 
tank,  from  which  it  is  de- 
livered to  the  "  carbonating 
tower"  (Fig.  42).*  This 
is  from  50  to  65  feet  high, 
built  of  cast-iron  rings  or 
segments  (A,  A),  each  about 
3.5  feet  high  and  6  feet  in 
diameter.  At  the  bottom 
of  each  segment  is  a  flat 
plate  having  a  large  hole 
in  the  centre.  Above  each 
plate  is  a  dome-shaped  dia- 
phragm (D)  perforated  with 
a  great  number  of  small 
holes.  In  modern  works 
a  system  of  pipes  passes 

through  each  segment,  as  shown  at  (B,  B);  in  these,  cold  water  is 
kept  flowing,  thus  counteracting  the  heat  generated  by  the  chemical 
action.  The  ammoniacal  brine  is  forced  under  pressure  through  the 
pipe  (P),  entering  a  little  above  the  middle  of  the  tower,  which  is 
nearly  filled  with  brine.  By  this  arrangement,  any  free  ammonia  in 
the  brine,  which  would  be  swept  away  by  the  stream  of  gases  passing 
up  through  the  tower,  is  taken  up  by  the  carbon  dioxide  in  the  upper 
part  of  the  tower.  The  carbon  dioxide,  having  been  previously  well 
cooled,  is  forced  through  the  pipe  (C),  entering  under  the  lowest 
dome,  and  rising  in  small  bubbles  through  the  perforations  in  each 

*  After  Lunge. 


FIG.  42. 


88  OUTLINES  OF  INDUSTRIAL   CHEMISTRY 

dome,  comes  into  intimate  contact  with  the  ammoniacal  brine.  The 
bicarbonate  of  sodium,  thus  precipitated  gradually  works  its  way 
down  through  the  tower.  A  thick,  milky  liquid,  containing  the 
bicarbonate  in  suspension,  and  ammonium  chloride  and  common  salt 
in  solution,  is  drawn  off  through  (H)  at  the  bottom. 

After  a  tower  has  been  in  use  for  some  days,  the  holes  in  the 
domes  become  clogged  with  a  deposit  of  bicarbonate  crystals,  which 
prevent  the  free  passage  of  the  gases.  Consequently,  every  ten 
days  or  two  weeks  the  liquid  must  be  drawn  out  and  the  crystals 
dissolved  by  filling  the  tower  with  hot  water  or  steam.  The  tower 
must  be  cooled  before  starting  the  process  anew.  As  a  rule,  several 
towers  are  employed,  so  that  one  may  be  cleaned  and  cooled  without 
interrupting  the  operation. 

The  gases  escaping  from  the  top  of  the  tower,  consisting  princi- 
pally of  nitrogen,  carbon  dioxide,  and  some  ammonia,  are  passed 
through  scrubbers  (p.  273),  one  of  which  contains  brine,  which  after- 
wards goes  to  the  ammonia  saturating  tank ;  in  the  other  is  dilute 
sulphuric  acid,  to  absorb  the  small  amount  of  ammonia  which  would 
otherwise  be  lost.  The  carbon  dioxide  and  nitrogen  are  allowed  to 
escape.  The  towers  are  run  with  the  view  to  the  utilization  of  all 
the  ammonia  possible,  even  though  there  is  considerable  loss  of  salt 
and  carbon  dioxide ;  usually  about  one-fourth  of  the  salt  remains 
undecomposed. 

It  is  now  customary  to  place  a  smaller  carbonating  tower  in  con- 
nection with  the  large  one ;  in  the  former  the  brine  is  first  treated 
with  carbon  dioxide  and  the  ammonia  converted  to  neutral  carbon- 
ate (NH4)2C03;  then  the  brine  is  pumped  into  the  large  carbonating 
tower,  where  it  meets  more  carbon  dioxide,  and  the  bicarbonate  is 
formed,  causing  the  precipitation  of  the  sodium  bicarbonate.  More 
heat  is  liberated  in  the  formation  of  the  neutral  carbonate  of  am- 
monia than  in  its  conversion  to  the  bicarbonate,  hence  the  tempera- 
ture of  the  precipitation  is  more  easily  controlled  when  two  towers 
are  used,  and  less  free  ammonia  escapes  with  the  waste  gases. 

A  temperature  of  about  35°  C.  is  most  favorable  to  the  formation 
of  a  granular  or  crystalline  precipitate  of  bicarbonate,  and  also  to 
the  most  complete  utilization  of  the  ammonia.  At  higher  tempera- 
tures, too  much  bicarbonate  remains  dissolved  in  the  liquor;  at 
lower  temperatures  there  is  a  tendency  to  the  crystallization  of 
ammonium  acid  carbonate  and  ammonium  chloride,  while  the  bicar- 
bonate separates  as  a  very  fine  precipitate,  which  is  difficult  to  filter 
from  the  liquor. 

The  milky  liquor  from  the  bottom  of  the  tower,  containing  the 


THE   SODA   INDUSTRIES  89 

sodium  bicarbonate  in  suspension,  is  filtered  on  sand  filters  (p.  15) 
connected  with  a  vacuum  pump ;  or  better,  it  is  run  into  centrifugal 
machines  (p.  14),  which  afford  more  rapid  and  complete  separation 
of  the  mother-liquor.  The  bicarbonate  is  then  washed  with  water, 
to  remove  as  much  of  the  sodium  and  ammonium  chlorides  as  pos- 
sible. The  mother-liquors  and  wash  waters  go  to  the  ammonia 
recovery  process. 

The  sodium  bicarbonate  is  then  calcined  in  large  covered  cast-iron 
pans  or  ovens ;  this  converts  the  acid  salt  into  soda-ash,  and  drives 
out  any  ammonia  or  moisture  still  in  the  mass.  The  following  is 
the  reaction :  — 

2  KaHC03  =  Na2CO3  +  CO,  +  H20. 

The  fumes  are  passed  through  coolers  and  scrubbers  to  remove 
ammonia;  the  concentrated  carbon  dioxide  remaining  is  pumped 
into  the  carbonating  towers.  The  ammonia  liquors  go  to  the 
ammonia  stills. 

A  modification  of  the  Thelen  pan  (Fig.  40,  p.  79)  is  sometimes 
used  for  this  calcining.  A  gas-tight  cover  is  placed  over  the  pan, 
and  the  scrapers  pass  back  and  forth  over  the  pan  bottom,  being 
moved  by  a  connecting  rod  and  crank.  The  gases  and  steam  pass 
off  through  a  pipe  set  in  the  cover.  In  practice,  it  has  been  found 
best  to  leave  the  mass  in  this  pan  only  until  all  the  ammonia  and 
about  75  per  cent  of  the  carbon  dioxide  of  the  bicarbonate  have 
been  expelled;  the  calcination  is  completed  in  a  reverberatory 
furnace. 

The  product  of  the  calcination  is  called  soda-ash ;  it  is  often  very 
pure,  containing  only  a  trace  of  salt  and  a  little  bicarbonate,  and 
is  free  from  caustic  soda,  sulphide,  and  sulphate.  But  its  density 
is  only  0.8,  while  that  of  the  Leblanc  product  is  1.2.  This  is  dis- 
advantageous, owing  to  the  larger  packages  needed  for  a  given 
weight  and  to  the  mechanical  loss  incurred  in  operations  where  the 
soda-ash  is  exposed  to  a  strong  draught  of  air.  In  order  to  increase 
the  density,  it  is  sometimes  subjected  to  a  second  heating  in  a  rever- 
beratory (revolving)  furnace. 

The  second  reaction,  on  p.  86,  is  that  on  which  the  recovery  of 
the  ammonia  depends.  The  liquid  in  which  the  bicarbonate  of  soda 
was  suspended  contains  undecomposed  salt,  ammonium  chloride,  and 
ammonium  carbonate.  It  is  passed  through  an  ammonia  still,  usu- 
ally a  tall  column  or  dephlegmator  (p.  8).  Steam  is  admitted  at 
the  bottom  of  the  apparatus,  and  bubbling  up  through  the  liquid, 
decomposes  the  ammonium  carbonate  into  ammonia,  carbon  dioxide, 


90  OUTLINES  OF  INDUSTRIAL   CHEMISTRY 

and  water;  the  ammonium  chloride  passes  down  into  the  lower 
part  of  the  tower,  or  the  still  proper,  where  it  is  decomposed  by 
"milk  of  lime."  The  ammonia  set  free  is  cooled  and  used  to 
saturate  the  brine.  The  calcium  chloride  formed  remains  in  solu- 
tion, and  together  with  the  excess  of  salt,  goes  to  waste.  (For  the 
various  proposals  to  utilize  the  waste  calcium  chloride  for  the  pro- 
duction of  hydrochloric  acid  and  chlorine,  see  p.  102.) 

The  damp  bicarbonate  is  dried  in  an  atmosphere  of  carbon  dioxide, 
at  a  temperature  of  about  90°  C. ;  this  prevents  decomposition  of  the 
sodium  bicarbonate,  while  the  ammonium  bicarbonate  is  decom- 
posed, the  vapors  passing  to  the  scrubbers,  where  the  ammonia  is 
recovered.  A  considerable  quantity  of  the  bicarbonate  of  soda  is  sold 
directly  to  the  manufacturers  of  baking  powder  and  the  poorer  grades 
to  the  soda-water  makers. 

Caustic  soda  can  be  made  stronger  and  purer  from  ammonia  soda- 
ash  than  from  Leblanc  ash,  and  the  process  is  not  essentially  differ- 
ent, except  that  no  treatment  to  remove  sulphur  is  necessary ;  but  it 
cannot  be  made  so  cheaply  as  from  the  "  red  liquors "  or  the  "  tank 
liquors  "  of  the  Leblanc  process.  If  pure  lime  is  used  for  causticiz- 
ing  ammonia  soda-ash,  the  product  is  better  than  in  the  case  of  the 
Leblanc  ash,  as  it  is  free  from  sulphur,  alumina,  etc. 

Loewig's  process  (p.  81)  appears  especially  suited  for  causticiz- 
ing  ammonia  soda-ash,  since  it  requires  an  ash  free  from  silica. 

The  Parnell  and  Simpson  process*  was  expected  to  solve  the 
problem  of  the  Leblanc  "  alkali  waste  " ;  but  while  it  is  interesting, 
it  has  not  justified  the  hopes  of  its  promoters.  It  was  proposed  to 
combine  to  a  considerable  extent  the  two  leading  soda  processes. 
The  reactions  involved  are  as  follows :  — 

1)  (NH4)2S  +  C02  +  H20  =  NH4HC03  +  NH4HS. 

2)  NH4HS  +  C02  -f  HaO  =  NH4HC03  +  H2S. 

3)  NH4HC03  +  NaCl  =  NaHC03  +  NH4Cl. 

4)  CaS  +  2  NH4C1  =  (NH4)2S  +  CaCl2  f 

A  solution  containing  a  mixture  of  ammonium  sulphide  and  salt 
is  treated  with  carbon  dioxide,  as  in  the  ammonia  process.  Sodium 
bicarbonate  is  precipitated  and  hydrogen  sulphide  set  free ;  this  is 
burned  with  air,  and  the  sulphur  dioxide  sent  to  the  lead  chambers 
of  the  sulphuric  acid  process.  Or  the  sulphur  may  also  be  recovered 
in  a  Glaus  kiln  (p.  85).  The  ammonium  sulphide  is  obtained  by 

*  J.  Soc.  Chem.  Ind.,  1889,  11. 

t  Equation  (4)  does  not  exactly  represent  the  facts,  as  some  polysulphides  are 
present  in  the  tank  waste. 


THE  SODA  INDUSTRIES 

boiling  the  alkali  waste  of  the  Leblanc  process,  with  the  ammonium 
chloride  liquors  of  the  ammonia  process,  or  those  formed  in  this 
(Parnell-Simpson)  process.  Thus  the  ammonia  is  recovered  and  at 
the  same  time  the  troublesome  Leblanc  waste  is  disposed  of. 

When  the  waste  is  boiled  in  the  ammonium  chloride  solution, 
ammonia  gas,  together  with  vapors  of  ammonium  sulphide,  is  lib- 
erated. These  are  led  directly  into  the  brine  solution  in  the  satu- 
rating tank.  The  ammoniacal  brine  is  then  pumped  into  the 
carbonatiug  tower,  which  is  very  similar  to  that  described  on  p.  87. 
Here  the  first  three  reactions  take  place ;  *  the  hydrogen  sulphide 
generated  goes  to  the  sulphur  recovery,  while  the  ammonium  chloride 
solution,  carrying  the  sodium  bicarbonate  in  suspension,  is  drawn  out 
and  filtered. 

The  conversion  of  salt  into  sodium  carbonate  by  any  method 
involves  an  endothermic  reaction  in  some  part  of  the  process.  Thus 
energy  must  be  expended,  necessitating  the  use  of  fuel.  In  the  case 
of  the  Leblanc  process,  this  expenditure  of  fuel  is  large,  and  is 
chiefly  used  in  carrying  out  the  reactions  in  the  salt-cake  and  the 
black-ash  furnaces.  But  much  of  the  expended  energy  of  this  pro- 
cess reappears  in  the  hydrochloric  acid,  the  principal  by-product. 

In  the  ammonia  process  the  principal  reactions  are  exothermic, 
but  some  fuel  is  consumed  by  the  calcination  of  the  precipitated 
bicarbonate  and  in  the  preparation  of  the  quicklime  used  in  the 
ammonia  recovery  and  for  generating  carbon  dioxide.  Although 
less  fuel  is  used  than  in  the  Leblanc  process,  the  practical  economy 
of  the  ammonia  process  is  not  so  great  as  would  at  first  appear ;  for 
all  the  chlorine  is  lost,  together  with  a  large  part  of  the  original  salt 
used.  As  a  method  of  producing  soda-ash  it  is  far  superior  to  the 
Leblanc,  but  until  a  practical  process  for  the  cheap  production  of 
chlorine  is  discovered,  the  latter  will  continue  to  be  an  extensive 
industry. 

*  According  to  Lunge,  Sulphuric  Acid  and  Alkali,  Vol.  Ill,  p.  157,  the  sodium 
bicarbonate  is  formed  by  agitating  the  brine  with  crystallized  ammonium  bicarbon- 
ate, the  latter  being  obtained  by  saturating  the  ammonium  sulphide  solution  with 
carbon  dioxide  (equations  1  and  2) .  The  carbon  dioxide,  which  must  be  very  pure 
and  concentrated,  is  made  by  heating  ammonium  bicarbonate  crystals  to  74°  C.,  in  a 
retort,  CO2,  steam,  and  NH3  passing  off.  By  scrubbing  (p.  273),  the  carbon  dioxide  is 
obtained  pure. 

Ammonium  bicarbonate  is  also  prepared  by  passing  lime-kiln  gases  into  a  solution 
of  ammonia  or  neutral  ammonium  carbonate,  and  then  cooling  it  to  crystallize  the 
bicarbonate. 


92  OUTLINES   OF  INDUSTRIAL  CHEMISTRY 


THE   CRYOLITE   SODA   PROCESS 

« 

Cryolite  is  a  double  fluoride  of  sodium  and  aluminum,  found  as 
a  mineral  in  southern  Greenland.  As  no  other  important  deposit 
has  been  found,  the  supply  is  limited,  and  only  two  or  three  manu- 
factories using  this  process  are  in  operation,  one  of  which  is  in  this 
country.  The  reactions  involved  are  as  follows :  — 

1)  A1F3  •  3  NaF  +  3  CaC03  =  NaAlO,  +  Na2O  +  3  CaF2  +  3  C02. 

2)  NaA102  +  Na20  =  Na3A103. 

3)  2  Na3A103  +  3  H20  +  3  CO2  =  3  Na2C03  +  2  Al  (OH)3. 

The  ground  cryolite  is  mixed  with  powdered  limestone,  and  calcined 
at  a  red  heat.  Carbon  dioxide  escapes,  and  a  mixture  of  calcium 
fluoride,  sodium  oxide,  and  sodium  aluminate  remains.  On  lixiviat- 
ing this  mixture  with  water,  another  sodium  aluminate  is  formed  and 
goes  into  solution,  leaving  the  calcium  fluoride  as  an  insoluble  resi- 
due. The  solution  of  sodium  aluminate  is  then  decomposed  according 
to  the  third  reaction,  by  passing  into  it  purified  lime-kiln  gases,  or 
the  furnace  gases  of  the  calcining  operation.  Hyd rated  alumina  is 
precipitated,  while  sodium  carbonate  remains  in  solution.  Sal-soda 
may  be  made  by  evaporating  the  solution,  and  was  formerly  the  chief 
source  of  bicarbonate  for  culinary  and  medicinal  purposes.  If  carried 
to  complete  dryness  and  calcined,  a  high  grade  of  soda-ash  is  obtained. 
By  causticizing,  it  yields  a  very  excellent  caustic. 

The  by-products  aluminum  hydroxide  and  calcium  fluoride  are 
used  in  the  alum  and  glass  industries  respectively. 

Many  other  processes  for  the  manufacture  of  soda  from  salt  have 
been  proposed,  but  none  of  them  are  now  of  any  commercial  impor- 
tance. A  small  amount  of  soda  is  still  made  from  kelp  or  varec, 
which  is  the  ash  of  seaweeds. 

A  new  process  for  making  soda  has  been  proposed,  *  which  is  in- 
teresting and  may  be  developed  in  the  future,  but  has  not  as  yet 
been  placed  on  a  practical  basis.  Salt-cake  is  made  from  salt  by  the 
Hargreaves  process  (p.  71) ;  then  in  the  same  cylinder  and  at  the 
same  temperature,  it  is  treated  with  water  gas.  This  reduces  the  salt- 
cake  to  sodium  sulphide,  while  water,  carbon  monoxide,  and  hydro- 
gen escape.  These  vapors  are  cooled,  the  water  condensed,  and  the 
mixture  of  gases  burned,  the  products  of  combustion,  carbon  dioxide 
and  water,  passing  into  the  cylinders  containing  the  sodium  sul- 

*  J.  Soc.  Chem.  Ind.,  1895,  933. 


THE  SODA  INDUSTRIES  93 

phide.  Hydrogen  sulphide  and  sodium  carbonate  are  formed,  and  as 
the  temperature  is  much  above  100°  C.,  no  water  can  combine  with 
the  carbonate.  The  hydrogen  sulphide  is  burned  to  sulphur  dioxide, 
and  the  latter  returned  to  the  Hargreaves  process.  The  reactions 
involved  are  as  follows  :  — 

1)  2  NaCl  +  S02  +  H20  +  O  =  Na2S04  4-  2  HC1. 

2)  Na2S04  +  5  CO  +  5  H2  =  Na2S  +  4  H20  +  5  CO  +  H2. 

3)  CO  +  H2  +  02  =  C02  +  H20. 

4)  Na2S  +  C02  +  H20  =  Na2C03  +  H2S. 

5)  H2S  +  3  O  =  H2O  +  S02. 

This  process   seems  to  offer  several  advantages  of  which  the 
following  are  the  chief :  — 

1.  Cheap  materials. 

2.  Small  outlay  for  labor,  —  the  materials  not  been  handled  from 
the  time   the  salt  is  charged  into  the  cylinders  until  the  soda-ash 
is  raked  out. 

3.  No  waste  products  nor  nuisance. 

4.  The  temperature   constantly  decreases,  being   highest  when 
the  furnace  is  charged  and  lowest  when  the  soda-ash  is  finished. 

5.  The  process  yields  hydrochloric   acid  which  can  be  utilized 
for  making  chlorine. 

For  the   methods   of  producing  caustic   soda  and  chlorine  by 
electrolysis  of  brine,  see  Chlorine,  p.  104. 

REFERENCES 

Berichte  ueber  die  Entwickelung  der  chemischen  Industrie.     A.  W.  Hoffmann, 

Vol.  I,  418.     (1875.). 
History,  Products,  and  Processes  of  the  Alkali  Trade.     Charles  T.  Kingzett, 

London,  1877.     (Longmans.) 
Manual  of  Alkali  Trade.     John  Lomas,  London,    1880.     (Crosby,  Lockwood 

and  Co.) 
J.  Soc.  Chem.  Ind :  — 

1883,  405,  Walter  Weldon. 

1885,  527,  Ludwig  Mond. 

1886,  412,  E.  K.  Muspratt. 

1887,  416,  Watson  Smith. 

1888,  162,  Alexander  Chance. 

1889,  11,  E.  Parnell. 

Sulphuric  Acid  and  Alkali.    G.  Lunge,  2d  ed.,  Vols.  II,  1895,  III,  1896.    (Gur- 
ney  and  Jackson,  London.) 


94  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 


CHLORINE   INDUSTRY. 

Chlorine  is  extensively  used  in  the  arts  as  a  bleaching  and 
oxidizing  agent.  It  is  chiefly  employed  in  the  form  of  a  solution 
of  "  bleaching  powder "  or  "  chloride  of  lime,"  which  contains  cal- 
cium hypochlorite,  and  as  chlorates  or  hypochlorites  of  the  alkali 
metals.  Liquid  chlorine,  compressed  in  steel  cylinders,  has  recently 
become  an  article  of  commerce,  and  it  appears  probable  that  this 
form  of  shipment  may  be  extended  in  the  future. 

Practically,  all  the  chlorine  used  in  the  arts  must  be  derived 
from  the  chlorides  of  sodium,  potassium,  or  magnesium,  which  are 
found  more  or  less  abundantly  in  nature.  A  very  large  part  of  the 
hydrochloric  acid  made  from  salt  (p.  67)  is  used  for  making  chlorine. 
Since  this  acid  is  the  chief  by-product  of  the  Leblanc  process,  a 
plant  for  making  bleaching  powder  is  always  a  part  of  those  works. 

The  important  methods  of  making  chlorine  from  the  acid  may 
be  considered  under  two  heads :  those  using  manganese  oxides  for 
decomposing  the  acid,  and  those  not  using  manganese  for  this 
purpose. 

The  function  of  manganese  is  to  oxidize  the  hydrogen  of  the 
acid,  forming  water  and  liberating  the  chlorine.  At  the  same  time, 
the  manganese  is  converted  into  chloride,  and  being  somewhat  ex- 
pensive, its  recovery  in  a  form  that  permits  of  its  return  to  the 
process  is  essential. 

The  oxides  of  manganese  are  found  in  nature  as  pyrolusite 
(Mn02),  braunite  (Mn203),  manganite  (Mn203  •  H20),  hausmannite 
(Mn304),  wad  and  psilomelane,  the  last  two  of  indefinite  composi- 
tion. The  reactions  occurring  when  manganese  oxides  are  treated 
with  hydrochloric  acid  are  as  follows  :  — 

1)  MnO    +  2  HC1  =  MnCl2  +  H20. 

2)  Mn02  +  4  HC1  =  MnCl2  +  2  H20  +  2  Cl. 

3)  Mn  A  +  6  HC1  =  2  MnCl2  +  3  H20  +  2  Cl. 

4)  Mn304  +  8  HC1  =  3  MnCl2  +  4  H2O  +  2  Cl. 

Thus  it  is  readily  seen  that  with  pyrolusite,  less  acid  is  neces- 
sary for  a  given  yield* of  chlorine,  and  a  smaller  quantity  of  man- 
ganous  chloride  must  be  treated  to  recover  the  manganese.  This 
ore  is  purchased  according  to  its  content  of  Mn02,  which  is  estimated 
by  determining  the  "  available "  oxygen.  The  presence  of  iron 
oxides,  silica,  calcium  carbonate,  etc.,  is  disadvantageous. 


CHLORINE    INDUSTRY 


95 


FIG.  43. 


In  small  works,  especially  where  no  at- 
tempt is  made  to  recover  the  manganese, 

the  process  is  carried  on  in  simple  stills  of 

earthenware  or  sandstone.     The   earthen- 
ware  stills  (Fig.  43)*   are  cheap,  but  of 

limited    capacity.      They    are    heated   by 

blowing  free  steam  into  the  wooden  casing 

in  which  they  are  set.      The  pyrolusite  is 

put  into  the  central  perforated  cylinder, 

and  the  acid  runs  through  the  pipe  (A), 

chlorine  escaping  at  (B).     Sandstone  stills 

(Fig.  44)*  are  made  from  single  blocks  of 

sandstone,  or  built  up  of  slabs,  the  joints 

being  made  tight  by  a  rubber  packing,  or  by  a  lute  of  clay  and  lin- 
seed oil.     The  pyrolusite  rests  on  a  false  bottom  (A),  and  the  acid 

is  run  in  through 
(B),  while  steam 
is  blown  in  through 
the  sandstone  pipe 
(C).  Chlorine  es- 
capes through  (D). 
These  stills  are 
larger  than  the 
earthenware  ones, 
but  do  not  utilize 
the  acid  so  com- 
pletely. 
The  pipes  through  which  chlorine  is  conducted  are  of  lead  or 

earthenware.      Since  valves  in   these   pipes  are  rapidly  corroded, 

a  device  shown  in  Fig.  45*  is  used  to 

shut  off  the  flow  of  gas.     A   U-shaped 

bend  is  made  in  the  pipe,  and  a  small 

flexible  tube  attached  at  the  lowest  point 

of  the  U,  connecting  it  with  the  vessel 

(A),  filled  with  water.      By  raising  (A), 

the  water  flows  into  and  fills  the  U-pipe 

to  the  line  (CD),  cutting  off  the  flow  of 

gas.     By  lowering  (A)  to  (Ar),  the  water 

runs  out  of  the  U,  and  the  flow  of  gas  is 

uninterrupted. 

The  liquor  remaining  in  the  still  con- 
*  After  Lunge. 


FIG.  44. 


96 


OUTLINES  OF  INDUSTRIAL  CHEMISTRY 


tains  much  free  acid,  manganous  chloride,  ferric  chloride,  etc.  It 
continues  to  evolve  some  chlorine  for  a  long  time,  and  is  a  very 
offensive  and  troublesome  material  to  dispose  of,  since  it  pollutes 
the  air,  or  the  streams,  into  which  it  passes. 

Of  the  many  attempts  to  recover  the  manganese,  the  two  follow- 
ing are  the  most  important :  — 

By  Dunlop's  method,  the  "  still  liquor  "  is  neutralized  cold,  with 
powdered  limestone,  until  all  free  acid  is  removed  and  the  iron  pre- 
cipitated. The  clear  solution  of  manganous  and  calcium  chlorides 
is  then  mixed  with  a  carefully  determined  quantity  of  powdered 
limestone  or  chalk,  and  heated  under  pressure  by  steam.  This 
precipitates  the  manganese  as  carbonate,  which  is  settled,  and  the 
solution  of  calcium  chloride  drawn  off.  The  manganous  carbonate 
is  washed,  and  then  calcined  at  about  300°  C.  in  a  retort,  while 
water  spray  and  a  current  of  air  is  introduced.  This  produces  a 
mixture  of  Mn02,  MnO,  Mn203,  etc.,  containing  about  70  per  cent 

of  the  dioxide.  The  process 
requires  an  expensive  plant 
and  consumes  a  large  amount 
of  fuel. 

The  Weldon  process,*  for 
manganese  recovery,  is  the 
most  successful,  and  is  in 
general  use  in  all  large  works, 
since  it  furnishes  a  continu- 
ous process  for  chlorine  mak- 
ing and  manganese  recovery. 
The  "  still  liquors  "  are  neu- 
tralized with  just  sufficient 
powdered  limestone  or  chalk 
to  remove  free  acid  and  pre- 
cipitate the  iron.  This  is 
done  in  the  tank  (A)  (Fig. 
46),f  provided  with  a  stirrer. 
The  mixture  is  then  pumped 
into  settling  tanks  (B,  B), 

where  the  precipitate  deposits.  The  clear  solution  of  manganous 
and  calcium  chlorides  is  then  drawn  into  the  "  oxidizers  "  (C),  where 
steam  is  blown  in  to  heat  it  to  55°  C.  Milk  of  lime  is  made  from  pure 
lime,  especially  free  from  magnesia,  and  is  added  from  (E)  until  tests 


FIG.  46. 


*  J.  Soc.  Chem.  Ind.,  1885,  525. 


f  After  Lunge. 


CHLORINE  INDUSTRY  97 

show  that  the  manganese  is  all  precipitated ;  meanwhile  air  is  slowly 
forced  into  (C).  The  quantity  of  "milk"  used  is  noted,  and  then 
from  one-half  to  one-quarter  more  is  added,  and  the  air  blast  turned 
on  at  full  strength.  This  addition  of  an  excess  of  lime  is  necessary 
to  hasten  and  complete  the  conversion  of  manganous  hydroxide  into 
the  peroxide,  and  to  prevent  the  formation  of  Mn304  ("  red  batch  "). 
The  total  quantity  of  lime  used  should  be  such  that  the  precipitate 
formed  during  the  blowing  contains  approximately  two  molecules 
of  manganese  peroxide  to  one  of  calcium  oxide.  This  is  the  so-called 
"  acid  calcium  manganite  "  (CaO  •  Mn02)  4-  (MnO  •  Mn02),  a  mixture 
of  manganites  of  calcium  and  manganese.  It  forms  a  thin,  slimy, 
black  mass,  and  is  called  "Weldon  mud."  By  adding  a  little  more 
neutralized  "  still  liquors  "  during  the  "  blowing,"  some  of  the  calcium 
oxide  in  the  calcium  manganite  can  be  replaced  by  manganese  from 
the  manganous  chloride  of  these  liquors. 

The  calcium  chloride  liquor,  in  which  the  mud  is  suspended, 
is  run  into  settling  tanks  (D,  D),  from  which  the  supernatant  solu- 
tion is  drawn  off  as  waste.  The  Weldon  mud  is  then  run  into  the 
chlorine  stills  (F,  F)  as  a  thin  paste;  if  of  good  quality,  it  contains 
about  80  per  cent  of  its  manganese  as  Mn02,  and  owing  to  its  fine 
state  of  division,  is  readily  decomposed  by  dilute  hydrochloric  acid. 

A  small  loss  of  manganese  occurs  in  the  precipitate  from  the 
first  neutralization  with  marble  or  chalk  dust;  this  loss  is  made 
up  by  decomposing  some  pyrolusite  with  hydrochloric  acid  in  a 
small  still  (G),  and  adding  this  liquor  to  that  from  the  stills  (F,  F). 

The  Weldon  process  works  continuously  and  almost  automatic- 
ally, the  materials  being  handled  by  pumps  as  liquids  or  slimes. 
It  is  also  very  rapid,  producing  large  amounts  of  chlorine,  with  but 
slight  loss  (2  to  3  per  cent)  of  manganese  oxide.  But  even  at  its 
best,  only  about  one-third  of  the  chlorine  of  the  hydrochloric  acid  is 
obtained  as  gas,  the  remainder  going  to  waste  as  calcium  chloride 
in  the  liquor  from  the  oxidizers. 

Schlosing's  process  *  for  chlorine  by  the  use  of  nitric  and  hydro- 
chloric acids  and  manganese  oxides  depends  upon  the  following 
reactions :  — 

2  HC1  +  2  HN03  +  Mn02  =  Mn(N03)2  4-  2  H20  +  C12. 

The  reaction  is  carried  out  by  heating  the  mixture  of  acids  and 
manganese  peroxide  to  125°  C.,  using  an  excess  of  nitric  acid.  By 
heating  the  manganous  nitrate  to  180°  to  190°  C.,  it  'is  decomposed, 

*  Zeit.  angew.  Chemie,  1893,  99,  Lunge  and  Pret.  Wagner's  Jahresbericht, 
1862,  235. 

H 


98  OUTLINES  OF  INDUSTRIAL   CHEMISTRY 

and  nitric  acid  may  be  regenerated   from    the  vapors   by  treating 
them  with  air  and  steam,  while  manganese  peroxide  is  recovered:  — 

Mn(N03)2  =  Mn02  +  N204  ; 


Wischin,  Just,  and  Alsberge  have  each  patented  modifications 
of  the  above  process.  Alsberge  proposes  to  apply  the  method  to  the 
recovery  of  chlorine  from  the  ammonium  chloride  liquors  of  the 
ammonia  soda  process,  by  employing  the  following  equations:  — 

1)  2NH4Cl+MgO+Mn02=MgCl2+Mn024-H20+2NH3. 

2)  MgCl2+Mn02+4  HNO3=Mg(N03)2+Mn(N03)2+2  H20  +01* 

By  evaporating  to  dryness  and  calcining  the  residue,  the  nitrates 
are  decomposed  thus  :  — 


Mg(N03)2  +  Mn(N03)2  =  MgO  +  Mn02  +  2  N204  +  0. 

The  peroxide  of  nitrogen  is  converted  to  nitric  acid  by  treatment 
with  steam  and  air  :  — 


Deacon's  process!  seems  to  be  the  most  successful  method  of 
producing  chlorine  without  the  use  of  manganese.  It  depends  on 
the  oxidation  of  hydrochloric  acid  gas,  by  the  oxygen  of  the  air. 
This  is  done  in  the  presence  of  certain  metallic  salts,  which  may 
act  as  "  contact  "  substances,  or  as  carriers  of  oxygen  from  the  air 
to  the  acid,  the  apparent  reaction  being  :  — 


The  most  satisfactory  "contact"  or  "  catalytic"  substance  for  this 
purpose  is  copper  chloride.  When  cupric  chloride  is  heated  to 
400°  C.,  it  dissociates  into  cuprous  chloride  and  free  chlorine. 
Then,  on  exposing  the  cuprous  chloride  to  oxygen,  cupric  oxide  is 
formed  and  more  chlorine  set  free.  But  the  cupric  oxide,  reacting 
with  hydrochloric  acid  gas,  forms  water  and  cupric  chloride.  The 
following  are  the  reactions  involved  :  — 

1)  2  CuCl2  =  Cu2Cl2  +  C12. 

2)  Cu2Cl2  +  02  =  2CuO  +  Cl2. 

3)  2  CuO  -f  4  HC1  =  2  CuCl2  +  2  H20. 

Thus  the  catalytic  substance  is  regenerated  and  the  cycle  of  changes 
begins  anew. 

t  Chemical  News  22  (1870),  157. 


CHLORINE   INDUSTRY 


99 


Heat  to  the  amount  of  32  calories  is  absorbed  during  the  disso- 
ciation of  cupric  chloride,  but  in  the  other  reactions  60.4  calories  is 
evolved.  Since  the  sum  of  the  reactions  represents  a  positive  gain 
of  28.4  calories,  theoretically  when  the  process  is  once  under  way  no 
addition  of  heat  is  necessary.  But,  in  fact,  some  heat  must  be  sup- 
plied ;  this  is  done  by  heating  the  mixture  of  air  and  hydrochloric 
acid  gas  to  400°  C.  before  admitting  it  to  the  "  decomposers."  Theo- 
retically, too,  all  the  chlorine  of  the  hydrochloric  acid  should  be 
recovered,  but  practically  the  reaction  is  far  from  complete. 


FTG.  4T. 


The  plant  for  the  process  (Fig.  47)*  is  quite  extensive.  The 
gases  from  the  salt-cake  pan  (A),t  together  with  air,  are  passed 
through  cooling  pipes  and  drying  tower  ( B)  to  condense  moisture ; 
then  they  go  through  the  "superheater"  (C),  where  the  temperature 
is  raised  to  400°  C.  The  hot  gases  then  pass  into  the  "decomposer" 
(D),  a  tall  cast-iron  cylinder,  containing  bits  of  brick  or  other  porous 
material  which  have  been  soaked  in  a  solution  of  cupric  chloride. 
Here  the  above  reactions  take  place,  and  the  resuMng  mixture  of 
chlorine,  hydrochloric  acid,  nitrogen,  steam,  and  oxygen,  passes 
through  a  condensing  apparatus  (E,  E)  to  remove  the  hydrochloric 
acid,  and  then  through  a  coke  tower  (F,  F)  sprinkled  with  concen- 
trated sulphuric  acid  to  remove  all  the  moisture;  finally,  the  dry 
chlorine  gas  (with  the  nitrogen  and  oxygen)  goes  to  the  chambers 
where  bleaching  powder  is  made  (p.  110). 

The  catalytic  substance  in  the  decomposer  becomes  inactive  after 
a  time  (it  seldom  lasts  more  than  four  months)  and  must  be  re- 
placed by  fresh  material.  To  accomplish  this  without  interrupting 
the  process  the  decomposers  are  now  built  in  separate  compartments, 
each  holding  about  six  tons  of  broken  brick ;  every  two  weeks  one 
compartment  is  emptied  and  recharged  without  discontinuing  the 
*  After  Lunge.  t  Roaster  gas  is  too  dilute  and  impure. 


100  OUTLINES  OF   INDUSTRIAL   CHEMISTRY 

flow  of  gas  through  the  others.  This  loss  of  activity  in  the  cata- 
lytic substance  is  attributed*  to  the  presence  of  sulphuric  acid  in 
the  gases  from  the  salt-cake  furnace.  To  overcome  this  difficulty, 
Hasenclever  has  devised  a  method!  by  which  an  aqueous  solution 
of  impure  hydrochloric  acid,  made  in  the  bombonnes  and  coke 
towers,  is  run  into  hot,  concentrated  sulphuric  acid  (1.42°  Tw.)  while 
a  blast  of  air  is  forced  through  the  mixture.  The  sulphuric  acid 
absorbs  the  water  and  generates  pure  HCl  gas,  which  mixes  with  the 
air  in  proper  proportion  for  use  in  the  decomposer  of  Deacon's 
process.  By  this  method,  84  per  cent  of  the  hydrochloric  acid  gas  is 
decomposed  according  to  the  reaction  :  — 

2HC1+0  =  H20  +  2C1. 

The  diluted  sulphuric  acid  is  concentrated  and  returned  to  the 
process.  The  dilute  hydrochloric  acid  which  passes  through  the 
apparatus  is  recovered  by  washing  the  chlorine  gas,  and  is  mixed 
with  the  strong  acid  from  the  roasters. 

Owing  to  the  admixture  of  nitrogen  with  the  chlorine,  the  latter 
is  weaker  than  that  furnished  by  the  Weldon  process.  It  is  well 
suited  for  making  chlorates  (p.  Ill),  but  for  making  bleaching  powder 
a  special  form  of  absorption  chamber  must  be  used. 

When  the  hydrochloric  acid  gas  is  taken  directly  from  the  salt- 
cake  pan  or  from  the  muffle  furnace,  there  is  apt  to  be  some  diffi- 
culty in  working  Deacon's  process,  owing  to  the  variation  in  the 
rate  of  liberation  of  the  gas.  Much  care  in  the  regulation  of  the  air 
supply  is  necessary. 

The  hydrochloric  acid  gas  from  the  Hargreaves  process  (p.  71) 
is  too  dilute  for  direct  use  in  the  Deacon  apparatus. 

Arsenic  in  'the  sulphuric  acid  used  in  the  salt-cake  pan,  or  for 
drying  the  chlorine  gas,  causes  a  loss,  —  in  the  first  case  by  rendering 
the  copper  salt  inactive,  and  in  the  second,  by  forming  hydrochloric 
acid,  thus  :  — 

+  4  Cl  +  2  H20  =  As205  +  4  HCl. 


Part  of  this  hydrochloric  acid  combines  with  the  As205  to  form 
a  solution  which  condenses  in  the  pipes  between  the  drying  tower 
and  the  bleaching  powder  chambers.  But  some  of  the  acid  is  left 
in  the  chlorine  and  attacks  the  bleaching  powder,  causing  it  to  be 
"  weak." 

The  cost  of  a  Deacon  plant  is  rather  more  than  of  a  Weldon 

*  Berichte  d.  chem.  Gesellschaft,  IX,  1070. 
t  Lunge,  Sulphuric  Acid  and  Alkali,  If,  417. 


CHLORINE        bttSTRY^VXv  \\\  \    ;.    101 

plant  of  the  same  capacity ;  and  while  it  is  theoretically  a  superior 
process  and  requires  less  labor,  it  is  not  yet  in  general  use. 

Several  processes  for  the  preparation  of  chlorine  by  the  use  of 
nitric  and  sulphuric  acids  have  been  proposed. 

Dunlop's  nitric  acid-chlorine  process  depends*  upon  one  or  the 
other  of  the  following  equations:  — 

2  NaCl  +  2  NaNO3  +  4  H2S04  =  4  NaHS04  +  N2O4  +  C12+  2  H20 ; 
4  NaCl  +  2  NaN03  +  6  H2S04  =  6  NaHS04  +  N203  +  2  C12  +  3  H20. 

The  mixture  of  salt,  sodium  nitrate,  and  sulphuric  acid  is  heated 
in  an  iron  cylinder  which  is  surrounded  by  the  flames  of  the  fire. 
The  vapors  leaving  the  retort  are  passed  through  concentrated  sul- 
phuric acid  which  retains  the  nitrogen  oxides,  and  the  chlorine  is 
then  washed  with  water  to  remove  any  traces  of  hydrochloric  acid. 

The  nitrous  vitriol  obtained  may  be  used  in  the  sulphuric  acid 
manufacture.  The  process  was  worked  on  a  large  scale  at  St.  Kol- 
lox,  England,  but  has  been  abandoned. 

Donald's  process  t  consists  in  passing  the  hydrochloric  acid  vapor 
from  a  salt-cake  furnace  through  sulphuric  acid  to  dry  it,  and  then 
through  a  mixture  of  nitric  and  sulphuric  acids  kept  at  0°  C.,  when 
the  following  reactions  take  place :  — 

2  HC1  +  2  HN03  =  2  H20  +  N204  +  C12. 

The  gas  mixture  thus  formed  is  led  through  dilute  nitric  acid, 
when  the  following  takes  place :  — 

N204  +  H20  =  HN03  +  HNO2. 

By  passing  through  concentrated  sulphuric  acid,  the  nitrous  acid 
and  nitrogen  oxides  are  absorbed,  while  the  chlorine  is  sent  to  the 
bleaching  powder  chambers. 

The  S adler- Wilson  $  nitric  acid-chlorine  process  consists  in  re- 
acting upon  hydrochloric  acid  with  nitric  acid,  in  the  presence  of 
sulphuric  acid;  the  operation  is  carried  on  in  a  heated  " decom- 
poser "  built  of  flagstones.  The  hot,  dilute  sulphuric  acid  is  again 
concentrated,  and  the  gases  from  the  decomposer  are  cooled  and 
passed  through  a  Gay  Lussac  tower  to  recover  the  nitrous  vapors. 
The  chlorine  is  washed  to  remove  free  hydrochloric  acid,  dried  and 
led  into  the  bleaching  powder  chambers. 

Many  attempts  have  been  made  to  recover  the  chlorine  from  the 
waste  liquors  of  the  ammonia  soda  process,  but  no  one  of  them  has 

»  Lunge,  Sulphuric  Acid  and  Alkali,  III,  566. 

t  Ibid.,  572. 

J  J.  Soc.  Chem.  Ind.,  1895,  865. 


102  OFTLI'NPS  OF   INDUSTRIAL   CHEMISTRY 

yet  proved  a  commercial  success.  Several  of  them  are,  however, 
interesting,  and  deserve  a  few  words. 

Solvay  conducted  elaborate  experiments  in  which  he  tried  to 
realize  the  reaction:  — 

CaCl2  +  Si02  +  O  =  CaSiOg  +  C12. 

But  calcium  chloride  is  very  stable,  and  its  decomposition  in  this 
way  is  incomplete,  and  requires  enormous  expenditure  of  heat, 
besides  that  used  in  evaporating  the  solution  of  calcium  chloride 
to  dryness. 

Magnesium  chloride  •  is  more  easily  decomposed  than  calcium 
chloride,  and  several  processes  have  been  devised,  based  on  the  use 
of  this  salt.  It  is  proposed  to  use  magnesium  oxide  or  hydroxide 
instead  of  lime  for  decomposing  the  ammonium  chloride  solution 
of  the  ammonia  process  ;  by  this,  magnesium  chloride  is  formed  and 
the  ammonia  gas  set  free.  Both  Solvay  and  Weldon,  within  a  few 
days  of  each  other,  patented  methods  for  carrying  out  this  idea. 
But  the  reaction  between  ammonium  chloride  and  magnesia  is  not 
complete,  and  the  solution  of  magnesium  chloride  obtained  is  dilute. 
Viewed  as  a  method  for  chlorine,  more  promising  results  were  ob- 
tained by  using  the  concentrated  magnesium  chloride  mother-liquors 
from  the  Stassfurt  industries  (p.  132),  or  from  other  manufacturing 
operations.  The  magnesium  chloride  solution  is  evaporated  to  dry- 
ness  at  a  very  low  temperature,  and  the  dried  chloride  is  decomposed 
by  passing  air  or  steam  over  it  while  heated  to  a  red  heat.  The 
reactions  are  as  follows  :  — 


2) 

The  hydrochloric  acid  obtained  is  used  in  the  Weldon  or  Deacon 
process. 

The  Weldon-Pechiney  *  process  was  the  most  successful  of  the 
magnesia  methods,  though  none  of  them  can  be  said  to  be  profitable. 
In  this,  magnesium  chloride  solution  (made  by  dissolving  the  oxide 
in  hydrochloric  acid,  or  obtained  from  waste  liquors)  is  concentrated 
until  it  contains  six  molecules  of  water  for  each  molecule  of  magne- 
sium chloride;  then  1-J-  equivalents  of  magnesium  oxide  is  stirred 
into  the  solution.  The  pasty  mass  heats  and  soon  hardens  to  a  solid 
cake  of  magnesium  oxychloride,  which  is  broken  into  lumps  about 
the  size  of  a  butternut,  and  screened  to  remove  the  dust.  The 
presence  of  dust  causes  the  mass  to  cake  badly  during  the  subse- 

»  J.  Soc.  Chem.  Ind.,  1887,  775. 


CHLORINE  INDUSTRY  103 

quent  drying.  The  lumps  are  dried  at  a  temperature  not  exceeding 
300°  C.,  by  passing  a  current  of  hot  air  over  them  while  spread  in 
a  thin  layer  on  gratings.  Too  high  temperature  causes  a  loss  of 
chlorine  as  such.  If  not  thoroughly  dried,  chlorine  is  lost  as  hydro- 
chloric acid.  The  dried  oxychloride  is  quickly  decomposed  in  a 
special  form  of  retort,  which  has  been  heated  by  producer  gas  to 
a  temperature  of  1000°  C.  before  the  charge  is  introduced.  Air  is 
passed  into  the  retort  to  assist  in  the  decomposition,  which  must 
be  rapid,  or  the  yield  of  chlorine  is  reduced.  Magnesium  oxide 
is  left  in  the  retort,  while  a  mixture  of  chlorine,  hydrochloric  acid, 
and  nitrogen  escapes.  The  hydrochloric  acid  is  recovered  by  wash- 
ing the  gases  with  water,  and  is  used  to  dissolve  part  of  the  oxide 
from  the  retort.  The  chlorine,  mixed  with  nitrogen,  is  used  for 
bleaching  powder,  or  for  chlorate  making,  preferably  the  latter. 
The  residue  of  magnesium  oxide  from  the  retorts  is  returned  to 
the  first  stage  of  the  process. 

The  yield,  including  the  hydrochloric  acid  recovered,  is  about 
88  per  cent  of  the  whole  amount  of  chlorine  in  the  magnesium 
chloride.  About  40  per  cent  is  obtained  as  free  chlorine,  and  48.5 
per  cent  is  returned  to  the  process  as  MgCl2  and  HC1. 

Of  the  several  methods  that  have  been  devised  for  the  direct 
production  of  chlorine  from  the  ammonium  chloride  formed  in  the 
ammonia  soda  industry,  Monet's  process,1*  which  provides  for  the  re- 
covery of  the  ammonia,  has  been  most  carefully  developed,  but  its 
practical  success  is  as  yet  problematical.  It  is  based  on  the  disso- 
ciation of  ammonium  chloride  into  ammonia  and  hydrochloric  acid, 
at  a  temperature  of  350°-360°  C. ;  the  hydrochloric  acid  being  then 
combined  with  some  metallic  oxide,  to  form  a  non-volatile  chloride, 
to  be  later  decomposed  with  liberation  of  the  chlorine.  Oxide  of 
nickel  was  used  at  first,  but  was  later  abandoned  in  favor  of  mag- 
nesium oxide.  The  reactions  are :  — 

1)  MgO  +  (2  NH3  +  2  HC1)  =  MgCl2  +  H20  +  2  NH3. 

2)  MgCl2  +  0  =  MgO  +  C12. 

Since  an  excess  of  magnesia  is  present,  it  is  very  probable  that 
considerable  magnesium  oxychloride  is  also  formed,  according  to  the 
reaction :  — 

2  MgO  +  2  HC1  =  MgO  -  MgCl2  +  H20. 

Then  this  is  decomposed  by  the  air  (reaction  2),  thus :  — 
MgO  •  2  MgCl2  +  0  =  2  MgO  +  C12. 

*Chemische  Industrie,  1892,  466.    J.  Soc.  Chem.  Ind.,  1887,  140,  216,  217,  440; 
1888,  626,  845. 


104  OUTLINES  OF   INDUSTRIAL  CHEMISTRY 

The  liberated  ammonia  passes  from  the  apparatus  to  the  scrub- 
bers of  the  ammonia  recovery  process.  The  complete  recovery  of 
this  ammonia  is  the  first  essential  to  the  success  of  this  method. 

The  ammonium  chloride  is  crystallized  from  the  liquors  of  the 
Solvay  carbonating  towers  (p.  87),  by  cooling  them  to  about  0°  C. 
The  dry  crystals  are  then  vaporized  by  introducing  them  into  melted 
zinc  chloride,  contained  in  an  iron  vessel  lined  with  an  antimony 
alloy. 

The  magnesium  oxide,  mixed  with  some  potassium  chloride,  china 
clay,  and  lime,  is  made  into  balls  ("pills"),  about  one-half  inch  in 
diameter,  and  baked.  The  decomposer  is  then  filled  with  the 
"pills'7  and  heated  to  360°  C.,  when  vapors  of  ammonium  chloride 
are  passed  through  the  apparatus.  The  reaction  between  the  ammo- 
nium chloride  and  magnesia  raises  the  temperature  in  the  decom- 
poser above  400°  C.  Next,  inert  gases,  such  as  those  from  lime- 
kilns, heated  to  550°  C,,  are  passed  into  the  apparatus  to  drive  out 
the  ammonia  and  water  vapors;  these  also  heat  the  charge  above 
500°  C.  Air,  heated  to  800°  C.,  is  then  admitted  to  break  up  the 
magnesium  chloride  (reaction  2)  and  regenerate  the  oxide ;  it  also 
sweeps  out  the  chlorine  formed.  After  cooling  to  360°  C.  ammonium 
chloride  vapors  are  again  introduced  and  the  cycle  of  operations  is 
repeated.  To  secure  uninterrupted  working,  there  are  usually  four 
decomposers  in  each  plant. 


ELECTROLYTIC  PROCESSES  FOR  CHLORINE  AND  CAUSTIC 

SODA 

By  passing  a  current  of  electricity  through  a  sodium  chloride 
solution  the  salt  is  decomposed  into  chlorine  at  the  anode  and 
sodium  at  the  cathode.  But  the  latter  at  once  decomposes  a  mole- 
cule of  water  of  the  solution,  forming  caustic  soda  and  setting  free 
hydrogen.  Hence  the  products  of  electrolysis  are  chlorine,  caustic 
soda,  and  hydrogen,  of  which  the  last  mentioned  is  of  no  practical 
value  at  present. 

There  are  serious  mechanical  difficulties  encountered  in  all  elec- 
trolytic processes  for  decomposing  salt.  The  chlorine  set  free  at  the 
anode  must  not  be  permitted  to  diffuse  through  the  whole  solution, 
since  it  causes  secondary  reactions.  To  prevent  this  diffusion,  vari- 
ous devices  have  been  proposed,  most  of  them  being  porous  dia- 
phragms between  the  anode  and  cathode.  But  no  material  is  yet 
known  which,  while  offering  no  resistance  to  the  passage  of  the 
electrical  current,  still  prevents  the  diffusion  of  the  sodium  hydroxide 


CHLORINE  INDUSTRY  105 

and  chlorine  solutions.  Furthermore,  very  few  substances  can  be 
used  for  the  diaphragms,  because  of  the  destructive  action  of  the 
chlorine.  The  nascent  chlorine  is  also  very  destructive  to  the  anode 
and  practically  only  platinum,  or  slabs  cut  from  magnetite  (Fe3O4), 
have  proved  efficient  in  withstanding  its  action.  These  are  expen- 
sive, and  magnetite  slabs  are  very  fragile.  If  the  hydrogen  liberated 
at  the  cathode  is  permitted  to  escape  through  the  solution,  it  stirs 
the  liquid,  aiding  the  diffusion  of  the  chlorine,  and  the  consequent 
formation  of  chlorates  and  hypochlorites,  thus :  — 

1)  Nad  =  Na  +  Cl. 

2)  Na  +  H2O  =  NaOH  +  H. 

3)  2  NaOH  +  2  Cl  =  NaCIO  +  NaCl  +  H2O. 

4)  3  NaCIO  =  NaC103  +  2  NaCl. 

5)  NaC103  +  6  H  =  NaCl  +  3  H20. 

Thus  reactions  3,  4  and  5  cause  a  loss,  since  they  regenerate  salt 
from  the  chlorine  set  free. 

LeSueur's  process*  formerly  employed  the  apparatus  described 
in  Lunge's  "Sulphuric  Acid  and  Alkali,"  Vol.  Ill,  p.  664.  The 
cathode,  of  iron  wire  gauze,  was  placed  in  a  slanting  position.  On 
it  rested  the  diaphragm,  consisting  of  two  parts, — a  sheet  of  parch- 
ment paper  and  a  double  sheet  of  asbestos  cemented  together  by 
blood  albumin,  coagulated  and  hardened  by  treatment  with  potas- 
sium bichromate.  An  earthenware  bell  enclosed  the  anode,  which 
was  made  of  lead,  carrying  carbon  rods  dipping  into  the  salt  solu- 
tion. Caustic  soda  was  formed  in  the  solution  outside  the  bell,  and 
owing  to  the  inclined  position  of  the  cathode,  the  hydrogen  was 
expected  to  escape  readily,  thus  preventing  polarization.  But  it 
proved  in  practice  that  the  earthenware  bells  were  disintegrated 
by  the  caustic  soda  solution,  while  the  hydrogen  set  free  on  the 
lower  side  of  the  cathode  did  not  ascend  along  the  sloping  dia- 
phragm and  escape,  but  diffused  through  it  and  found  its  way  into 
the  interior  of  the  cell.  This  resulted  in  forming  a  dangerous 
mixture  of  hydrogen  and  chlorine,  and  it  is  said  that  several  serious 
explosions  occurred.  Consequently  the  form  of  the  cell  has  been 
altered;  but  no  facts  regarding  the  improved  cell  can  be  given, 
owing  to  the  secrecy  maintained  about  its  construction  and  working. 
The  diaphragms  are  rapidly  destroyed,  lasting  only  from  24  to  48 
hours.  The  anodes  are  consumed  more  slowly,  lasting  about  six 
weeks.  The  process  yields  a  solution  of  caustic  containing  10  per 
cent  NaOH. 

*  J.  Soc.  Chem.  Ind.,  1892,  963;  1894,  453. 


106  OUTLINES  OF  INDUSTRIAL   CHEMISTRY 

In  Carmichael's  apparatus,*  an  asbestos  diaphragm,  impregnated 
with  Portland  cement,  is  used.  The  diaphragm  rests  horizontally 
on  the  cathode  at  the  bottom  of  the  cell ;  above  it  is  a  bell  to  collect 
the  hydrogen  given  off.  The  anode  is  a  grating  of  copper  rods, 
covered  with  hard  rubber,  through  which  numerous  platinum  points 
project  into  the  brine.  This  anode  is  suspended  in  the  top  of  the 
cell,  and  the  chlorine  set  free  is  thus  only  momentarily  in  con- 
tact with  the  liquid.  The  salt  solution  is  fed  into  the  cell  at  the 
top,  in  a  rapid  stream  of  drops  while  the  mixture  of  caustic  soda 
and  salt  flows  continuously  from  the  bottom.  The  supply  of  brine 
is  so  regulated  that  the  caustic  formed  at  the  cathode  is  drawn  off 
before  it  has  time  to  diffuse  through  the  liquid.  The  solution  drawn 
from  the  cell  contains  about  20  per  cent  of  caustic  soda,  and  about 
75  per  cent  of  the  salt  is  decomposed.  The  reaction  is  carried  on  at 
a  temperature  of  about  80°  C.  in  the  top  of  the  cell  near  the  anode, 
while  the  region  around  the  cathode  is  kept  as  cool  as  possible. 
Being  removed  from  the  immediate  action  of  the  chlorine,  the  dia- 
phragms are  very  durable. 

Greenwood's  apparatus!  consists  of  an  iron  vessel,  coated  with 
electrolytically  deposited  copper ;  this  is  made  the  cathode,  and  in 
it  is  placed  a  circular  anode  coated  with  carbon.  Between  the 
anode  and  the  vessel  walls  is  a  diaphragm  made  up  of  a  series  of 
V-shaped  circular  troughs  of  glass  or  porcelain,  fitted  together,  the 
spaces  between  them  being  packed  with  asbestos.  The  chlorine 
from  the  anode  chamber  is  led  away  by  suitable  pipes,  and  the 
caustic-salt  solution  passes  into  another  similar  cell,  where  more  of 
the  salt  is  decomposed.  The  cells  are  placed  en  cascade,  the  brine 
flowing  from  the  top  one,  down  through  the  series.  The  solution 
obtained  in  this  process  contains  about  2.2  per  cent  NaOH. 

In  the  Holland  and  Richardson  process  $  the  cathode  is  covered 
with  cupric  oxide.  The  hydrogen  liberated  here  reduces  the  oxide 
to  metallic  copper,  and  polarization  is  prevented.  If  caustic  soda  is 
desired,  the  cathode  is  placed  horizontally  at  the  bottom  of  the  cell. 
The  caustic  solution  formed,  being  heavy,  remains  on  the  cathode, 
while  the  chlorine  "escapes  from  the  anode  at  the  top.  When 
"  bleaching  liquors  "  or  hypochlorites  are  desired,  the  anode  is  put 
at  the  bottom  of  the  cell  and  the  cathode  at  the  top.  In  this  case 
the  chlorine  rises  through  the  caustic  solution  and  is  absorbed :  — 

2  NaOH  +  01,  =  NaOCl  +  NaCl  +  H20. 

*  Zeitschr.  f.  angew.  Chemie,  1896,  537. 

t  J.  Soc.  Chem.  Ind.,  1891,  642.  J  Ibid.,  1891,  699. 


CHLORINE   INDUSTRY 


107 


The  Hargreaves-Bird  process  *  employs  an  asbestos  diaphragm, 
impregnated,  with  Portland  cement,  or  with  clay  and  sodium  silicate  j 
it  is  fastened  on  a  wire  gauze  and  placed  in  a  horizontal  position. 

To  avoid  the  use  of  a  diaphragm,  numerous  processes  have  been 
proposed  in  which  mercury  is  used  as  the  cathode  or  is  placed 
between  the  anode  and  cathode. 

The  Hermite  process  t  has  attracted  much  attention  as  a  method 
of  making  bleaching  and  disinfecting  liquors  from  magnesium  or 
sodium  chloride  solutions;  but  it  is  not  used  for  the  production 
of  free  chlorine  or  caustic. 

The  Castner  process  $  appears  to  be  the  most  promising  of  the 
methods  using  mercury  between  the  anode  and  cathode.  The  cell 
(Fig.  48)  is  divided  into  three  com- 
partments, the  two  outside  ones 
containing  brine  and  the  carbon 
anodes  (A),  while  the  middle  one 
contains  the  caustic  solution  and 
the  iron  cathode  (C).  The  sodium 
set  free  is  taken  up  by  the  mercury, 
forming  an  amalgam.  The  cell  is 
made  to  rock  slightly  by  the  cam 
(E),  and  the  motion  carries  the 
mercury  and  amalgam  into  the  centre  compartment,  where  the  amal- 
gam acts  as  the  anode  during  the  passage  of  the  current  to  the 
cathode,  the  sodium  being  liberated.  A  regulated  supply  of  water 
flows  into  the  centre  compartment  continuously,  while  a  corre- 
sponding amount  of  caustic  solution  overflows  into  a  collecting 
tank,  the  process  being  thus  uninterrupted.  Each  cell  is  about 
6  feet  by  3  feet  by  6  inches,  and  will  decompose  about  56.5  pounds 
of  salt  daily,  producing  38.5  pounds  of  caustic  and  34.5  pounds 
of  chlorine  per  each  3.5  horse-power.  The  electrodes  being  near 
together,  there  is  but  little  resistance,  and  the  voltage  is  only 
about  4,  with  a  current  of  550  amperes.  The  wear  and  tear  is  said 
to  be  small.  The  process  is  claimed  to  yield  a  20  per  cent  solution 
of  caustic,  free  from  hypochlorites,  while  the  chlorine  gas  is  very 
pure,  containing  only  a  little  hydrogen.  The  mercury  seldom  con- 
tains more  than  0.02  per  cent  of  sodium,  which  is  removed  electro- 
lytically.  No  hypochlorites  are  produced,  and  the  electrical  efficiency 
is  claimed  to  be  over  88  per  cent. 

*  J.  Soc.  Chem.  Ind.,  1895, 1011. 

t  Ibid.,  1888,  292.     Zeitschr.  f.  angew.  Chem.,  1893,  301. 

|  Engineering  and  Mining  Journal,  1894  [58],  270. 


FIG.  48. 


108  OUTLINES  OF  INDUSTRIAL   CHEMISTRY 

Although  electrolytic  processes  have  been  much  elaborated  within 
the  last  decade,  the  difficulties  encountered  in  preventing  the  forma- 
tion of  hypochlorites  and  regeneration  of  the  salt,  the  destructive 
action  of  the  chlorine  and  caustic  on  the  diaphragms  and  other  parts 
of  the  apparatus,  and  the  large  size  of  plant  needed  for  a  compara- 
tively small  output,  have  deterred  most  manufacturers  from  engaging 
on  a  large  scale  in  such  an  uncertain  enterprise.  Then,  too,  except  in 
those  favored  places  where  water  power  can  be  had  cheap,  the  elec- 
tricity must  be  generated  by  means  of  boiler,  engine,  and  dynamo,  a 
method  which  consumes  much  fuel  with  low  efficiency.  The  electro- 
motive force  needed  to  decompose  sodium  chloride  is  a  little  over 
two  volts,  but  the  resistance  of  the  bath,  together  with  polarization, 
increases  the  tension  to  from  3.5  to  4  volts.  A  current  of  one  ampere 
at  4£  volts  will  yield,  theoretically,  0.00292  pounds  of  chlorine  and 
0.0033  pounds  of  caustic  soda  per  hour.  Cross  and  Bevan*  calculate 
that  with  an  efficiency  of  80  per  cent,  caustic  soda  costs  £12  10s. 
per  ton,  and  bleaching  powder  £7  10s.  per  ton,  when  produced  by 
electrolysis.  According  to  Haussermann,f  one  ampere,  with  80  per 
cent  efficiency,  yields  28.56  grams  of  NaOH  and  25.2  grams  Cl  in 
24  hours,  the  voltage  being  3.5.  Thus  35  amperes  are  needed  to 
produce  one  kilo  of  NaOH  in  24  hours. 

If  a  theoretical  yield  were  obtained,  the  chlorine  evolved  would 
make  about  100  pounds  of  bleaching  powder  for  each  40  pounds  of 
caustic  soda  produced.  But  the  latter,  which  is  in  much  greater 
demand  than  bleaching  powder,  can  be  made  more  cheaply  from 
ammonia  soda ;  therefore  it  would  seem  that  if  electrolytic  methods 
prove  successful  in  the  future  their  expansion  would  be  limited 
to  supplying  bleaching  powder  and  chlorates,  and  the  caustic  be 
regarded  as  a  by-product.  Moreover,  the  caustic  liquors  produced 
by  electrolysis  are  dilute,  necessitating  much  evaporation,  and  the 
product  is  contaminated  with  much  chloride  and  chlorate. 

HYPOCHLORITES 

By  passing  chlorine  into  a  cold  solution  of  sodium  or  potassium 
carbonate,  a  mixture  of  the  chloride  and  hypochlorite  of  the  alkali 
metal  is  formed.  But  if  any  excess  of  chlorine  is  introduced,  the 
hypochlorite  is  decomposed  into  chloride  and  free  hypochlorous 
acid  (HOC1)  :  — 

1)  K2C03  +  H20  +  2  Cl  =  KC1  +  KOC1  +  H20  +  C02. 

2)  K2C03  +  H,0  +  4  Cl  =  2  KC1  +  C02  +  2  HOC1. 

*  J.  Soc.  Chem.  Ind.,  1892,  963.  t  Zeitschrift  f.  Electrochemie,  1895,  21. 


CHLORINE   INDUSTRY  109 

This  solution  of  hypochlorous  acid  is  a  powerful  bleaching  and 
oxidizing  agent.  It  was  first  made  about  1789,  and  brought  into 
trade  in  France  as  a  "  bleach  liquor "  under  the  name  of  eau  de 
Javelle,  or  eau  de  Labarraque.  In  1798  or  1799  Charles  Tennant 
took  out  a  patent  in  England  for  a  "  bleach  liquor  "  made  by  passing 
chlorine  into  "milk  of  lime,"  by  which  a  solution  of  calcium  chloride 
and  hypochlorite  was  formed :  — 

2  Ca  (OH)2  +  4  Cl  =  CaCl2  +  Ca  (OC1)2  +  2  H2O. 

This  bleach  liquor  is  cheaper,  stronger,  and  more  convenient  to  use 
than  bleaching  powder  (see  below),  but  since  it  is  unstable,  evolving 
oxygen  even  when  kept  in  a  closed  vessel  in  the  dark,  it  is  usually 
made  only  for  immediate  use. 

The  tanks  in  which  the  milk  of  lime  is  treated  with  chlorine  are 
provided  with  stirring  apparatus ;  the  temperature  must  not  rise 
much  above  30°  C.,  or  chlorates  are  formed  (p.  111).  A  dilute 
chlorine  may  be  used.  The  density  of  the  solution  obtained  is 
about  8°  Tw. 

Calcium  carbonate  suspended  in  water  may  also  be  employed  for 
preparing  bleach  liquor :  — 

CaC03  +  H20  +  4  Cl  =  CaCl2  +  C02  +  2  HOC1. 

These  liquors  are  chiefly  used  for  bleaching  vegetable  fibres  and 
for  disinfectants. 

The  absorption  of  chlorine  in  milk  of  lime  soon  led  to  trials  of 
dry,  slaked  lime  or  calcium  hydroxide  for  the  same  purpose.  A  dry 
bleaching  powder,  fairly  stable  and  constant  in  strength,  resulted ; 
but  its  composition  is  not  the  same  as  that  of  the  bleach  liquor  made 
from  milk  of  lime.  It  was  at  first  supposed  that  a  direct  combina- 
tion took  place  between  the  lime  and  chlorine,  and  that  the  powder 
was  simply  calcium  hypochlorite  [Ca(OCl)2],  so  the  name  "chloride 
of  lime  "  was  given  to  it.  Other  investigations  led  to  the  view  that 
it  contained  a  mixture  of  calcium  chloride  and  hypochlorite.  But 
this  was  disproved  by  Lunge  *  and  his  students ;  Lunge  assigns  to 

/Cl 

it  the  formula  Ca<^  .     Hence  it  is  an  oxy chloride  of  calcium. 

\0-C1 

When  dissolved  in  water,  this  forms  hypochlorite  and  chloride  of 
calcium. 

*Chemische  Industrie,  1881,  289.  Dingl.  J.,  237,  63.  Annalen  der  Chemie, 
219,  129.  Berichte  d.  deutch.  chem.  Gesellschaft,  1887, 1474.  Zeit.  f .  anorg,  Chemie, 
II,  311. 


110  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

For  making  bleaching  powder,  a  very  pure,  fat  lime  (p.  148)  is 
desirable.  It  is  slaked  carefully,  so  that  the  resulting  hydroxide 
contains  about  24.5  to  25.5  per  cent  of  water.  That  is,  there  should 
be  a  slight  excess  of  water  over  that  necessary  to  form  calcium 
hydroxide. 

The  absorption  chambers  are  brick,  cast  iron,  or  lead,  and  are 
usually  6.5  feet  high,  and  have  about  200  square  feet  of  floor  area 
per  ton  of  bleach  made  per  week.  Brick  chambers  are  tarred  inside 
to  make  them  gas  tight  and  to  protect  them  from  the  chlorine; 
large  ones  are  usually  made  from  lead,  much  like  the  vitriol  cham- 
bers (p.  52),  and  may  have  a  floor  area  of  30  by  100  feet.  The  slaked 
lime  is  sifted  through  screens  with  from  20  to  25  meshes  per  linear 
inch,  as  only  the  fine  powder  is  suitable.  This  is  spread  three  or 
four  inches  deep  on  the  floor,  and  is  furrowed  with  a  special  rake 
in  order  to  assist  the  absorption  by  increasing  the  surface.  The 
chlorine  is  introduced  at  the  top  of  the  chamber,  and  settling  to  the 
bottom  because  of  its  density,  is  at  first  rapidly  absorbed  by  the  lime. 

After  a  time  the  process  goes  on  more  slowly,  and  finally  the  gas 
enters  under  some  pressure.  In  modern  works  there  are  three  or 
more  chambers  in  a  series,  the  strongest  chlorine  entering  that  con- 
taining the  most  nearly  finished  bleach,  and  passing  out  through 
that  containing  the  fresh  lime.  The  degree  of  absorption  of  chlorine 
is  judged  by  the  color  of  the  gases  seen  through  the  glass  "  sights  " 
in  the  chamber  walls.  The  powder  is  turned  over  once  or  twice, 
and  the  treatment  ("gassing")  continued  until  tests  show  that  it 
contains  from  36  to  37  per  cent  of  "available  chlorine."  If  under 
strength  ("  weak  "),  after  the  third  "  gassing,"  it  should  be  packed 
and  sold  for  what  it  will  bring,  for  further  exposure  will  cause  the 
formation  of  chlorate  and  chloride  with  loss  of  strength. 

During  the  absorption  considerable  heat  is  generated ;  for  strong 
powder  the  temperature  should  not  exceed  40°  —  46°  C.  *  The  chlo- 
rine should  be  admitted  in  a  very  slow  stream,  and  should  be  con- 
centrated, dry,  and  free  from  hydrochloric  or  carbonic  acids.  When 
dilute  (as  from  Deacon's  apparatus),  a  large,  special  chamber  pro- 
vided with  numerous  shelves,  on  which  the  slaked  lime  is  spread 
to  secure  a  greater  absorbing  surface,  is  employed.  The  yield  from 
100  pounds  of  good  lime  is  about  150  pounds. 

Bleaching  powder  is  a  yellowish  white  substance,  which  should 
be  perfectly  dry  and  free  from  lumps.  On  exposure  to  the  air,  it 
absorbs  moisture  and  carbon  dioxide,  giving  off  hypochlorous  acid, 

*  Lunge  and  Schappi,  Dingl.  J.,  237,  63. 


CHLORINE  INDUSTRY  HI 

the  evolution  of  which  gives  bleach  its  peculiar  odor.  Good  samples 
contain  about  36  per  cent  "  available  chlorine."  Its  chief  use  is  for 
bleaching  vegetable  fibres  for  the  textile  and  paper  industries. 

In  order  to  liberate  the  chlorine  for  bleaching  purposes,  the  powder 
is  usually  decomposed  by  a  mineral  acid,  thus :  the  fibre  having  been 
saturated  with  the  bleaching  powder  solution,  is  passed  into  a  dilute 
acid  bath,  where  the  hypochlorite  is  decomposed  and  the  chlorine 
set  free.  The  nascent  chlorine  combines  with  the  hydrogen  of  the 
water,  liberating  nascent  oxygen,  which,  in  turn,  destroys  the  organic 
coloring  matter  in  the  fibre. 

/ 

CHLORATES 

Potassium  and  sodium  chlorates  are  usually  made  by  Liebig's 
process,*  in  which  double  decomposition  between  calcium  chlorate 
and  a  chloride,  sulphate,  or  carbonate  of  the  alkali  metal  is  accom- 
plished. If  the  chlorine  is  passed  into  a  hot  potash  or  soda  solution, 
and  the  liquid  evaporated,  a  very  small  yield  of  chlorate,  with  a 
large  quantity  of  chloride,  is  obtained :  — 

3  K2C03  +  6  Cl  =  5  KC1  +  KC103  +  3  CO* 

There  is  also  difficulty  in  separating  the  chloride  and  chlorate. 
In  Liebig's  process  chlorine  is   passed  into  milk  of  lime  at  or 
above  a  temperature  of  100°  C. ;  the  apparent  reaction  being :  — 

a)       6  Ca  (OH)2  +  6  C12  =  5  CaCl2  +  Ca  (C103)2  +  6  H2O. 
But  this  may  comprise  two  minor  reactions,  viz. :  — 

2  Ca  (OH),  +  2  Cl,  =  CaCl2  +  Ca  (OC1)2  +  2  H2O ; 
3  Ca  (OC1)2  =  2  CaCl2  +  Ca  (CIO,)* 

It  is  possible,  however,  that  the  hypochlorite  may  decompose 
thus :  — 

Ca(OCl)2  =  CaCl2-f  02, 

causing  waste  of  chlorine.  To  prevent  this,  an  excess  of  chlorine 
must  always  be  present.  Theoretically,  only  one  molecule  of  cal- 
cium chlorate  is  obtained  from  12  atoms  of  chlorine.  This  would 
yield  two  molecules  of  potassium  chlorate,  according  to  the  re- 
action :  — 

6)  Ca  (C103)2  +  2  KC1  =  CaCl2  +  2  KC103. 

But  the  actual  yield  is  only  about  70  per  cent  of  the  theoretical, 
since  much  of  the  potassium  chlorate  is  lost  in  the  mother-liquor. 

*  Annalen  der  Pharmacie,  41 ,  307. 


112  OUTLINES   OF  INDUSTRIAL   CHEMISTRY 

The  hot  milk  of  lime  is  saturated  with  chlorine,  in  tanks  pro- 
vided with  agitators,  and  when  the  liquor  has  a  density  of  25°  to 
30°  Tw.,  it  is  run  off  and  settled.  The  clear  solution  is  then  mixed 
with  the  calculated  quantity  of  potassium  chloride  (which  should 
be  purified,  since  sodium  or  magnesium  chloride  is  difficult  to  separate 
from  the  product) ;  the  resulting  solution  of  potassium  chlorate  is 
evaporated  in  wrought  iron  pans,  to  a  density  of  70°  Tw.  tested  in 
the  hot  liquor.  On  cooling,  the  chlorate  crystallizes  nearly  pure,  and 
the  mother-liquor,  containing  about  20  per  cent  KC103,  goes  to  waste. 
The  crude  chlorate  is  purified  by  recrystallizing  from  water,  and  the 
purified  crystals  are  drained  and  washed  carefully  in  a  centrifugal 
machine,  and  may  be  sold  as  coarse  crystals;  or  they  are  ground  to 
a  fine  powder  in  buhrstone  mills,  care  being  taken  that  no  organic 
matter,  dirt,  or  metal  (iron,  etc.)  gets  into  the  mill,  lest  an  explosion 
result.  No  fire  should  be  permitted  in  the  building,  and  heating 
should  be  by  steam,  and  lighting  by  electricity.  The  grinding  mill 
should  be  at  a  little  distance  from  the  main  building. 

Magnesia*  is  sometimes  substituted  for  lime,  in  order  to  increase 
the  yield  of  potassium  chlorate,  since  the  latter  is  much  less  soluble 
in  a  magnesium  chloride  solution  than  in  one  of  calcium  chloride. 
Thus  a  yield  of  90  per  cent  can  be  obtained,  owing  to  more  com- 
plete separation  when  crystallizing.  In  this  process  chlorine  is 
passed  into  a  "milk"  of  powdered  magnesia  in  water,  forming  a 
solution  of  magnesium  chloride  and  chlorate,  which  is  then  con- 
centrated until  crystals  of  magnesium  chloride  (MgCl2  •  6  H20) 
separate  on  cooling.  These  are  removed,  and  the  proportion  .  of 
chlorate  to  chloride  in  the  mother-liquor  is  about  1  Mg(C103)2  to 
2.8  MgCl2.  The  theoretical  quantity  of  potassium  chloride  is  then 
added,  and  potassium  chlorate  separates,  leaving  the  magnesium 
chloride  in  solution.  Any  excess  of  potassium  chloride  must  be 
avoided,  since  it  would  combine  with  the  magnesium  chloride  to 
form  a  crystalline  precipitate  of  a  double  salt  (MgCl2  •  KC1  •  6  H20 
—  artificial  carnallite),  which  would  contaminate  the  product.  The 
mother-liquors  might  be  worked  for  chlorine,  according  to  the  Wel- 
don-Pechiney  process  (p.  102). 

Sodium  chlorate  is  much  more  soluble  than  potassium  chlorate, 
and  is  more  difficult  to  crystallize.  Pechiney  devised  a  method  for 
its  production  by  which  a  solution  of  calcium  chloride  and  chlorate, 
made  by  treating  milk  of  lime  with  chlorine,  is  evaporated  to  a 
density  of  100°  Tw.  Then,  by  cooling  the  solution  to  exactly  12°  C., 
a  part  (f)  of  the  calcium  chloride  crystallizes  as  CaCl2  •  2  H2O,  leav- 
*  J.  Soc.  Chem.  Ind.,  1887,  248. 


CHLORINE  INDUSTRY  113 

ing  about  one  molecule  of  chloride  to  one  of  chlorate  in  the  liquor. 
Sodium  sulphate  is  then  added,  which  precipitates  calcium  sulphate, 
and  leaves  sodium  chloride  and  chlorate  in  solution.  On  concen- 
trating, sodium  chloride  crystallizes  and  is  "fished"  out  of  the 
warm  liquor,  which,  on  cooling,  deposits  crystals  of  sodium  chlorate; 
these  are  recrystallized. 

The  process  depends  on  the  fact*  that  a  saturated  solution  of 
the  mixed  salts  at  12°  C.  contains  24.4  grams  NaCl  and  50.75  grams 
NaC103  in  100  c.c.,  but  at  the  boiling  point  (122°  C.)  a  saturated 
solution  contains  only  11.5  grams  NaCl,  with  249.6  grams  N~aC103; 
hence,  on  cooling  to  12°  C.,  all  the  NaCl,  and  only  58.6  grams  of 
NaC103,  remain  in  solution,  the  remaining  181  grams  NaC103  crys- 
tallizing. This  process  has  been  largely  used  in  France. 

Chlorate  is  formed  by  the  electrolysis  of  a  potassium  chloride 
solution,  when  conducted  in  such  a  manner  that  the  alkali  formed 
around  the  cathode  comes  into  contact  with  the  chlorine  set  free  at 
the  anode,  the  temperature  being  kept  above  50°  C.  No  hypochlorite 
can  exist  at  this  temperature,  and  if  the  liquid  is  concentrated,  the 
chlorate  crystallizes. 

In  the  Gall  and  Montlaur  process,  a  25  per  cent  solution  of  potas- 
sium chloride  is  decomposed  by  a  current-density  of  50  amperes  per 
square  decimeter,  the  tension  of  each  bath  being  5  volts.  About  45 
per  cent  of  the  theoretical  yield  is  obtained,  the  mother-liquor  being 
again  saturated  with  chloride  and  returned  to  the  process.  The 
reactions  are  probably  as  follows  :  — 

2  KOH  +  Cl  =  KC10  +  KC1  +  H20  ; 

3  KC10  =  KC103  +  2  KC1, 

the  hypochlorite  being  instantly  decomposed  by  the  temperature  of 
the  bath.  The  hydrogen  set  free  in  the  bath  may  cause  part  of  the 
loss :  — 

KC103  +  6  H  =  KC1  +  3  H2O. 

Sodium  chlorate  may  be  formed  in  the  same  way,  but  being  more 
soluble,  does  not  precipitate  as  crystals,  and  hence  a  larger  propor- 
tion of  it  is  destroyed  by  the  reducing  action  of  the  hydrogen. 

REFERENCES 

Berichte  tiber  die  Entwickelung  der  chemischen  Industrie,  Dr.  A.  W.  Hofmann, 

Vol.  I,  Braunschweig,  1875.     (Vieweg.) 
Die  Fabrication  von  chlorsaurem  Kali  und  anderen  Chloraten.    Dr.  Conrad  W. 

Jurisch,  Berlin,  1888.     (R.  Gaertner.) 

*  Lunge,  Sulphuric  Acid  and  Alkali,  Vol.  Ill,  547. 


114  OUTLINES   OF  INDUSTRIAL   CHEMISTRY 

Die  Darstellung  von  Chlor  u.  Salzsaure,  unabhangig  von  der  LeBlanc  Soda 

Industrie.     Dr.  N.  Caro,  Berlin,  1893.     (R.  Oppenheimer. ) 
Sulphuric  Acid  and  Alkali.     G.  Lunge,  2d  ed.,  Vol.  Ill,  London,  1896.     (Gur- 

ney  and  Jackson.) 
J.  Soc.  Chem.  Ind :  — 

1883,  103,  Ferdinand  Hurter. 
1885,  525,  W.  Weldon. 
1887,  248,  C.  Longuet  Higgins. 
1887,  775,  James  Dewar. 
1896,  713,  Ludwig  Mond. 

Zeit.  f.  angew.  Chem.,  1893,  301.     (Hermite  and  Dubos§  Process.) 
Electro-Chemistry.     M.  Leblanc,  translated  by  W.  R.   Whitney,  Ph.D.,  New 

York,  1896.     (Macmillan  &  Co.) 
Elements  of  Electro-Chemistry.    Lupke. 


NITRIC   ACID 

The  manufacture  of  nitric  acid  is  very  often  combined  with  that 
of  sulphuric,  especially  in  those  factories  where  the  former  is 
employed  in  making  the  vitriol.  Large  quantities,  however,  are 
produced  for  general  manufacturing  purposes. 

Practically  all  nitric  acid  is  now  made  by  treating  sodium  nitrate 
(p.  119),  with  sulphuric  acid,  in  cast-iron  retorts.  The  reactions  are 
as  follows  :  — 


H2S04  =  NaHS04  +  HN03. 
2)  2  NaN03  +  H2S04  =  Na2S04  +  2  HN03. 

In  practice,  the  quantities  of  material  iised  do  not  correspond 
with  either  of  these  equations,  but  the  charge  is  so  regulated  that  a 
mixture  of  acid  and  neutral  sulphates  of  sodium,  which  remains 
liquid  at  the  temperature  employed,  is  left  in  the  retort.  If  reaction 
(1)  were  followed,  too  much  sulphuric  acid  would  be  used  for  profit- 
able working,  except  in  soda  works,  where  the  resulting  acid  sulphate 
might  be  used  in  the  salt-cake  furnace.  If  reaction  (2)  is  carried 
out,  the  temperature  must  be  very  high,  the  neutral  sulphate  solidifies 
in  the  retort  and  is  difficult  to  remove,  and  the  resulting  nitric  acid 
may  be  partly  decomposed  by  the  heat  before  it  can  escape  from  the 
retort,  thus  causing  a  diminished  yield  and  a  product  discolored  by 
the  oxides  of  nitrogen  produced. 

The  sulphuric  acid  employed  is  usually  that  from  the  lead  pan 
evaporation  (sp.  gr.  1.70),  but  for  nitric  acid  above  1.38  sp.  gr.,  oil  of 
vitriol  of  66°  Be.  is  used,  although  this  decomposes  part  of  the  nitric 
acid  formed.  The  sodium  nitrate  used  is  the  purified  Chili  saltpetre, 


NITRIC   ACID 


115 


containing  from  98  to  99  per  cent  of  NaN03,  when  dried.  It  should 
be  free  from  sodium  chloride  to  avoid  contaminating  the  nitric  acid 
with  hydrochloric  acid.  The  size  of  the  charge  depends  on  the 
capacity  of  the  plant,  but  in  some  more  modern  factories  it  amounts 
to  as  much  as  1200  pounds  of  nitrate,  with  somewhat  more  than  an 
equal  weight  of  sulphuric  acid  (sp.  gr.  1.70). 

The  old  style  of  plant  consisted  of  a  horizontal  cast-iron  cylinder, 
5  or  6  feet  long,  set  over  a  fireplace  in  such  a  way  that  the  flames 
played  over  the  sides  and  top,  heating  all  parts  to  a  high  tempera- 


ture.  Another  and  better  form  of  plant  is  shown  in  Fig.  49,  in  which 
the  cast-iron  retort  (A)  is  entirely  surrounded  by  the  flames  from 
the  grate.  Cast  iron  is  but  little  attacked  by  concentrated  nitric 
acid  or  its  vapors,  and  it  is  important  to  keep  the  retort  hot  enough 
in  all  parts,  to  prevent  condensation  of  the  acid.  A  more  mod- 
ern retort  is  shown  in  Fig.  50.  In  the  lower 
part  of  the  retort  is  a  pipe,  by  which  the 
melted  residue  of  "nitre  cake"  is  run  off, 
after  the  reaction  is  finished.  For  condensing 
the  acid  vapors  which  escape  from  the  retort, 
a  series  of  glass  or  earthenware  Woulfe  bottles 
(bombonnes)  (B,  B,  Fig.  49)  are  employed.  The 
first  two  or  three  of  these  bottles  are  generally 
placed  over  the  flue  by  which  the  fire  gases 
pass  to  the  chimney.  Being  thus  warmed, 
there  is  less  danger  of  breakage  by  the  high 
heat  of  the  vapors  from  the  retort.  At  the 
end  of  the  series  is  usually  placed  a  coke 

tower,  fed  with  water  or  concentrated  sulphuric  acid,  to  condense 
the  fumes  escaping  from  the  bombonnes.  Usually,  no  water  is  ad- 
mitted to  the  bombonnes  unless  a  dilute  acid  is  required ;  but  they 
are  sometimes  placed  en  cascade,  to  allow  the  condensed  acid  to  flow 


116 


OUTLINES  OF   INDUSTRIAL   CHEMISTRY 


through  the  series  in  a  direction  opposite  to  the  movement  of  the 
acid  vapors. 

The  most  concentrated  acid  is  condensed  in  the  first  two  or  three 
bombonnes,  but  is  contaminated  with  sulphuric  acid  and  nitrogen 
oxides.  The  last  of  the  series  contains  dilute  acid,  which  is  con- 
taminated with  chlorine.  In  the  middle  bottles  is  a  pure  acid  of 
moderate  strength.  Owing  to  more  or  less  reduction  of  the  nitric 
acid  in  the  retort,  the  condensed  acid  has  a 
yellow  or  red  color,  due  to  the  absorbed  nitrous 
vapors.  These  are  undesirable  in  a  commer- 
cial acid,  and  must  be  removed  by  "bleach- 
ing "  j  the  acid  is  heated  to  about  90°  C.,  and 
warm  air  blown  in.  which  carries  away  the 
nitrogen  oxides,  and  is  then  passed  through 
the  coke  tower  for  their  recovery. 

Guttmann's  apparatus  *  is  more  modern. 
The  large  cast-iron  retort  (Fig.  51)  is  made  in 
three  pieces  and  is  entirely  surrounded  by  the 
flames  from  the  grate.  The  gases  from  the 
retort  pass  into  a  system  (Fig.  52)  of  vertical  earthenware  pipes 
(AA),  having  very  thin  walls  and  joined  at  the  top  by  180°  bends, 
while  they  open  at  the  bottom  into  a  nearly  horizontal  collecting 


FIG.  51. 


FIG.  52. 


pipe  (BB),  which  is  divided  into  chambers  by  diaphragms.  These 
chambers  are  joined  by  U -tubes,  passing  under  the  diaphragms. 
The  diaphragms  force  the  acid  vapors  to  pass  up  one  pipe  and  down 


*  J.  Soc.  Chem.  Ind.,  1893,  203. 


NITRIC   ACID 


117 


the  next,  in  order  to  go  through  the  system.  The  thin  walls  (8  mm.) 
of  the  vertical  pipes  allow  very  efficient  cooling  by  exposure  to  the 
air  alone,  or  they  may  be  placed  in  a  tank  of  cold  water,  as  repre- 
sented in  the  figure.  By  this  very  rapid  cooling,  the  acid  vapors 
are  condensed  quickly.  Hot  air  at  80°  C.  is  injected  from  (F)  into 
the  outlet  pipe  (D),  where  it  converts  some  of  the  nitrous  vapors 
to  nitric  acid,  increasing  the  yield  materially.  (The  uncondensed 
nitrous  vapors  pass  into  the  Lunge-Rohrmann  plate  tower  (E)  (p.  58), 
where  the  nitrogen  oxides  are  absorbed  in  sulphuric  acid  or  water.) 
If  the  vapors  remain  in  the  retort  too  long,  part  of  the  acid  is  decom- 
posed, and  nitrogen  peroxide  is  formed,  and  absorbed  by  the  con- 
densed acid,  to  which  it  imparts  a  red  color.  But  since  there  is  a 
good  draught  through  the  apparatus,  the  vapors  are  drawn  out  of 
the  retort  very  soon  after  they  are  evolved,  and  are  at  once  con- 
densed. Thus  very  little  peroxide  is  formed,  and  a  light  colored, 
concentrated  acid  is  obtained  directly.  It  is  claimed  that  acid  of 
40°  Be.  (1.38  sp.  gr.),  requiring  no  "  bleaching/'  may  be  thus  made, 
and  that,  with  water-cooled  pipes,  98  per  cent  of  the  theoretical  yield 
is  obtained  as  concentrated 
acid,  while  2  per  cent  con-  -M  E 

denses   in   the    Lunge-Eohr- 
mann  tower. 

Hart's  tube  condenser 
(Fig.  53),  for  nitric  acid,  is  a 
new  form  of  apparatus.  It 
is  made  of  glass  and  earthen- 
ware tubes,  and  is  placed 
above  the  brick  arch  cover- 
ing the  retort,  thus  occupy- 
ing but  little  floor  space. 
The  vapor  from  the  retort 
(A)  passes  into  the  pot  (B), 
and  thence  through  the  ver- 
tical earthenware  tube  (C). 
From  (C)  to  (D)  extend  a 
number  of  glass  tubes,  which 
are  slightly  inclined  towards 

(C),  and  which  are  cooled  by  jets  of  water  from  the  perforated 
pipe  (EE).  From  (D),  the  uncondensed  vapors  pass  to  a  Lunge 
tower  or  a  coke  tower.  The  acid  condensed  in  the  glass  tubes  flows 
back  into  (C),  and  then  into  ( B),  thus  coming  into  contact  with  the 
hot  vapors  from  the  retort.  This  heats  the  acid  so  hot,  that  all  the 


FIG.  53. 


118  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

nitrous  vapors  are  driven  out  of  it.  From  (B),  the  acid  flows  through 
the  U-tube  (F)  into  bottles  or  carboys.  In  this  apparatus,  the  acid 
is  condensed  very  quickly  and  but  little  nitrogen  peroxide  is  formed. 
If  frothing  occurs  in  the  retort,  the  overflow  is  caught  in  the  pot  (B), 
and  may  be  removed  without  difficulty.  The  flow  of  water  from 
(E)  can  be  so  regulated  that  all  or  nearly  all  of  it  is  evaporated  on 
the  surface  of  the  glass  tubes,  thus  securing  the  greatest  cooling 
effect,  with  small  consumption  of  water.  Any  condenser  water  not 
evaporated  is  caught  in  the  trough  (G).  The  chief  repairs  are  of 
broken  tubes,  which  are  cheaply  and  easily  replaced. 

The  strength  of  the  nitric  acid  produced  in  any  apparatus  depends 
upon  the  strength  of  the  sulphuric  acid,  on  the  temperature  of  the 
retort,  and  on  the  purity  of  the  sodium  nitrate.  With  sulphuric  acid 
of  1.71  sp.  gr.,  the  nitric  acid  varies  from  1.38  to  1.42  sp.  gr.  (40°to 
42°  Be.).  If  the  sodium  nitrate  contains  chlorides,  some  of  the  nitric 
acid  is  decomposed  by  the  hydrochloric  acid  produced  ;  thus  :  — 

HN0  +  HC1  =  H0  +  N"0  +  Cl. 


It  is  claimed  that  with  Guttmann's  apparatus,  an  acid  of  1.5  to 
1.52  sp.  gr.  (50°  Be.),  containing  about  95  per  cent  HN03,  can  be 
made. 

For  chemically  pure  acid,  perfectly  pure  materials  should  be 
used,  although  formerly  the  common  acid  was  purified  by  treating 
with  silver  and  barium  nitrates,  and  redistilling.  But  concentrated 
acid  cannot  be  distilled  without  some  decomposition,  and  the  product 
must  be  "  bleached  "  by  heating  and  blowing  in  pure  air. 

Fuming1  nitric  acid  is  a  solution  of  nitrogen  peroxide  in  concen- 
trated nitric  acid.  It  is  red  in  color  and  has  a  specific  gravity  of 
1.55  to  1.62.  To  make  this,  perfectly  dry  sodium  nitrate  and  oil  of 
vitriol  (1.84  sp.  gr.)  are  used.  The  reaction  is  carried  so  far  that 
neutral  sulphate  of  sodium  is  formed  by  the  action  of  the  acid  sul- 
phate on  the  nitrate  :  — 

2  NaN03  +  2  NaHS04  =  2  Na2S04  +  2  N02  +  H20  +  0. 

The  nitrogen  peroxide  formed  dissolves  in  the  nitric  acid  to 
form  the  fuming  acid.  A  little  powdered  starch  is  sometimes  added 
to  assist  in  the  reduction  of  the  nitric  acid.  An  impure  fuming  acid 
is  sometimes  prepared  by  distilling  a  mixture  of  concentrated  nitric 
and  sulphuric  acids. 

Nitric  acid  is  largely  used  in  the  manufacture  of  explosives  ;  for 
parting  gold  and  silver  j  in  the  manufacture  of  coal-tar  dyes  ;  as  a 


NITRIC   ACID  119 

"pickling  liquor"  for  cleaning  metal;  and  in  the  manufacture  of 
various  metallic  nitrates.  It  is  a  colorless  liquid,  boiling  at  86°  C., 
but  with  decomposition.  (See  above.)  The  pure  acid  also  decom- 
poses on  exposure  to  strong  light  and  becomes  yellow  (N02).  When 
it  acts  on  metals,  the  hydrogen  liberated  at  once  reduces  some  of 
the  nitric  acid  itself,  setting  free  various  oxides  of  nitrogen,  of  which 
nitric  oxide  is  the  most  prominent.  Ordinary  commercial  nitric 
acid  (1.42  sp.  gr.)  distills  at  123°  C.,  and  contains  about  68  to  69  per 
cent  HISTOg,  and  corresponds  nearly  to  the  formula  2  H]ST03+3  H2O. 
The  very  concentrated  acid  of  1.50  sp.  gr.  contains  about  94  per 
cent  HN03. 

The  acid  sodium  sulphate  left  in  the  retort  after  making  nitric 
acid  is  called  "  nitre  cake,"  and  is  often  used  in  the  charge  for  mak- 
ing sulphate  in  the  Leblanc  process. 

Various  other  processes  for  making  nitric  acid  have  been  sug- 
gested, but  owing  to  the  low  price  of  Chili  saltpetre,  none  of  them 
are  now  in  use.  An  ingenious  proposal  to  use  the  "  still  liquors  " 
from  the  chlorine  manufacture,  instead  of  sulphuric  acid  for  decom- 
posing sodium  nitrate,  is  based  on  the  following  reactions  :  — 

1)   10  NaN03  +  5  MnCl2  =  2  MnO  +  3  Mn02 


2) 
3)   2 

This  permits  the  manganese  to  be  recovered  in  a  form  suitable 
for  use  in  the  chlorine  stills  again.  The  "  still  liquor  "  is  evaporated 
to  dryness,  the  pulverized  residue,  mixed  with  dry  sodium  nitrate, 
and  the  mixture  heated  to  about  230°  C.  in  a  retort.  .Reaction  (1) 
takes  place,  and  the  gases,  consisting  of  a  mixture  of  nitrogen  per- 
oxide and  oxygen,  are  led  into  a  tower  and  condensed  with  water  as 
per  reaction  (2).  The  nitric  oxide  produced  is  treated  with  air  and 
steam  and  condensed  according  to  reaction  (3). 

NITRATES 

The  most  important  nitrates  are  those  of  sodium  and  potassium, 
but  ammonium,  lead,  iron,  silver,  strontium,  and  barium  nitrates 
are  used  to  some  extent  in  the  arts. 

Sodium  nitrate,*  also  called  Chili  saltpetre,  is  found  in  natural 
deposits  in  desert  regions  along  the  west  coast  of  South  America, 
especially  near  the  boundary  lines  between  Peru,  Chili,  and  Bolivia, 

*  J.  Soc.  Chem.  Ind.,  1890,  664;  1893,  128. 


120  OUTLINES  OF  INDUSTRIAL   CHEMISTRY 

in  latitude  20°  to  26°  S.  The  territory  is  now  chiefly  owned  by 
Chili.  The  deposits  extend  about  220  miles  in  length,  and  average 
about  two  miles  in  width. 

The  crude  nitrate,  called  "caliche"  varies  from  yellowish-white 
to  brown  or  gray,  and  contains  from  20  to  55  per  cent  NaN03;  it 
forms  beds  about  5  feet  thick,  lying  near  the  surface,  but  usually 
covered  by  a  conglomerate  of  rock  debris,  cemented  together  by  salt 
and  gypsum.  The  region  is  rainless,  and  water  and  fuel,  being  very 
scarce,  are  used  as  economically  as  possible  in  refining  the  crude 
ore.  The  caliche  is  crushed  and  boiled  with  water  in  tanks  heated 
by  steam  coils,  until  the  liquor  reaches  a  density  of  110°  T\v.,  when 
it  is  run  off  to  crystallize.  The  mother-liquor  retains  most  of  the 
chloride,  iodide,  and  iodate  of  sodium  and  magnesium,  together  with 
about  20  per  cent  of  the  nitrate.  Hence  the  liquors  are  diluted  with 
the  wash  water  from  the  residue,  and  used  again  to  lixiviate  another 
portion  of  caliche.  But  after  two  or  three  repetitions  of  this  process, 
the  mother-liquor  is  too  contaminated  for  further  use.  It  is  then 
run  off  and  treated  for  the  recovery  of  the  iodine  (p.  218),  which  it 
contains.  The  residue  from  the  lixiviation  contains  some  nitrate, 
and  is  washed  with  fresh  water,  yielding  a  weak  solution,  which  is 
used  to  dilute  the  mother-liquors  before  using  them  for  leaching. 
The  sodium  nitrate  crystals  are  drained  or  "  centriffed "  and  dried 
in  the  sun.  They  are  then  packed  and  shipped  as  crude  Chili  salt- 
petre, containing  from  94  to  98  per  cent  of  NalSTOs.  For  many  pur- 
poses this  is  purified  by  recrystallization. 

Large  deposits  of  a  very  high  grade  of  sodium  nitrate  have  been 
found  recently  in  Upper  Egypt  and  in  the  trans-Caspian  region,  but 
these  have  not  been  much  developed  as  yet,  and  nearly  all  the 
world's  supply  comes  from  Chili. 

The  formation  of  these  beds  is  attributed  to  the  decomposition 
of  sea-plants  under  such  conditions  of  temperature  and  humidity 
that  the  ammonia  produced  was  converted  into  nitrate  by  the  action 
of  the  nitrifying  bacillus,  an  organism  found  in  the  soil.  The  region 
being  rainless,  the  sodium  nitrate  was  not  washed  away. 

Potassium  nitrate,  or  saltpetre,  is  derived  from  three  sources :  — 

1.  Natural  nitrate  beds,  formed  by  the  decomposition  of  organic 
matter  in  warm,  damp  climates. 

2.  Artificial  nitrate  beds,  prepared  especially  for  the  purpose. 

3.  The  decomposition  of  sodium  nitrate  by  potassium  chloride. 
In   many   tropical   countries,    especially  in   India,   Persia,   and 

Egypt,  native  deposits  of  potassium  nitrate  are  found  impregnating 
the  earth  in  the  neighborhood  of  large  cities  and  towns.  This 


NITRIC    ACID  121 

formation  is  due  to  the  action  of  the  nitrifying  bacteria,  and  is  not 
strictly  an  oxidation  process.  The  deposits  are  continually  form- 
ing, a  white  efflorescence  appearing  on  the  surface  of  the  ground. 
This  is  scraped  up,  lixiviated  with  water,  and  the  clarified  solution 
evaporated  directly,  to  crystallize  the  nitre.  But  all  the  calcium 
nitrate  in  the  mother-liquors  is  thus  lost.  By  adding  potash  ob- 
tained from  wood  ashes  the  calcium  nitrate  is  decomposed,  and  a 
larger  yield  of  nitre  is  obtained. 

The  artificial  production  of  saltpetre  in  beds  of  decaying  organic 
matter  is  now  of  slight  importance,  though  formerly  largely  prac- 
tised in  Sweden,  Switzerland,  and  France  when  nitre  was  collected 
as  a  part  of  each  farmer's  tax.  By  this  process  putrefying  organic 
matter  is  mixed  with  old  mortar,  or  with  porous  earth  containing 
calcium  carbonate  and  wood  ashes,  and  the  pile  allowed  to  stand  for 
some  months,  being  occasionally  moistened  with  the  liquid  drainage 
from  stables.  The  nitrifying  organisms  soon  impregnate  the  mass 
with  nitrates  of  calcium,  potassium,  and  magnesium.  On  leaching, 
these  go  into  solution;  when  boiled  with  wood  ashes,  the  calcium 
and  magnesium  are  precipitated  as  carbonates,  while  the  clarified 
liquor  yields  potassium  nitrate  on  concentrating.  The  solution  is 
clarified  by  adding  a  little  glue,  which  combines  with  the  impurities, 
forming  a  scum,  which  is  removed  by  skimming. 

Potassium  nitrate,  made  by  double  decomposition  of  sodium 
nitrate  with  potassium  chloride,  is  now  the  most  important  from  a 
commercial  standpoint.  The  reaction  is  very  simple :  — 

NaN03  +  KC1  =  NaCl  +  KNT03. 

Commercial  potassium  chloride,  containing  about  80  per  cent  KC1,  is 
dissolved  in  water  in  cast-iron,  copper,  or  lead  lined  wood  tanks  hold- 
ing 500  to  600  gallons.  When  the  hot  solution  has  a  density  of 
about  40°  to  42°  Tw.  (1.20  to  1.21  sp.  gr.),  sodium  nitrate  containing 
95  per  cent  NaK03  is  added,  and  the  boiling  mixture  well  stirred  for  an 
hour.  On  evaporation,  the  common  salt,  being  less  soluble  than  the 
nitrate,  precipitates,  and  as  much  as  possible  of  it  is  "  fished "  out, 
the  concentration  being  continued  until  the  density  of  the  solution 
is  100°  Tw.  (1.50  sp.  gr.).  The  liquid  is  allowed  to  stand  a  short 
time  to  settle,  and  then,  while  still  hot,  is  drawn  from  the  sediment 
into  crystallizing  tank?,  where  it  is  actively  stirred  while  cooling. 
This  causes  the  separation  of  the  nitre  as  " crystal  meal"  (p.  16), 
which  is  washed  with  a  saturated  solution  of  potassium  nitrate  (or 
often  with  cold  water)  to  remove  the  mother-liquor  and  remaining 
sodium  chloride.  The  wash  waters  and  mother-liquors  are  used  to 


122  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

dissolve  the  next  lot  of  potassium  chloride.  One  or  two  recrystal- 
lizations  free  the  potassium  nitrate  from  all  but  a  trace  of  chloride. 

When  the  potassium  chloride  contains  some  magnesium  chloride, 
it  is  best  to  precipitate  the  magnesium  by  soda-ash  before  adding 
the  sodium  nitrate,  since  traces  of  magnesium  chloride  may  other- 
wise remain  in  the  product.  This  salt,  being  deliquescent,  may 
cause  the  nitrate  to  become  wet  on  exposure. 

The  chief  uses  of  potassium  nitrate  are  for  making  gunpowder 
and  explosives,  in  matches,  in  pyrotechnics,  in  assaying,  in  metal- 
lurgical and  analytical  operations,  and  for  curing  meat. 

Ammonium  nitrate  is  now  used  to  a  considerable  extent  in  the 
manufacture  of  certain  "nameless  "  explosives,  and  also,  in  a  less  de- 
gree, for  making  nitrous  oxide  ("  laughing  gas  ").  It  is  usually  made 
by  neutralizing  nitric  acid  with  ammonia.  Attempts  to  produce  it 
by  double  decomposition  of  sodium  nitrate  with  ammonium  salts 
result  in  incomplete  reactions,  and  some  sodium  nitrate  remains  un- 
decomposed. 

Lead  nitrate  is  generally  made  by  dissolving  litharge  (PbO)  in 
hot  dilute  nitric  acid.  After  filtering,  the  solution  is  concentrated 
to  a  density  of  100°  Tw.  (1.50  sp.  gr.)  and  allowed  to  crystallize. 

It  is  used  in  dyeing  and  calico  printing,  for  the  manufacture  of 
certain  orange  and  yellow  pigments  (chrome  yellows),  for  some 
explosives,  and  in  some  kinds  of  matches.  It  is  important  in  that 
it  furnishes  a  moderately  soluble  lead  salt. 

Ferric  nitrate  (nitrate  of  iron)  is  generally  made  by  dissolving 
scrap  iron  in  nitric  acid  of  1.30  sp.  gr.  The  reaction  is  as  follows :  — 

2  Fe  +  8  HN03  =  2  Fe(N03)3  +  2  NO  +  4  H20. 

By  concentrating  the  solution,  colorless  crystals,  containing  six  or 
nine  molecules  of  crystal  water,  are  obtained. 

The  aqueous  solution  will  dissolve  ferric  hydroxide,  and  this  basic 
solution  is  much  used  in  textile  coloring.  By  using  an  excess  of 
iron,  and  permitting  the  reaction  to  continue  slowly,  after  all  the 
acid  has  been  acted  upon,  a  precipitate  of  insoluble  basic  ferric 
nitrate  ultimately  forms.  The  solution  obtained  in  this  way  is  of  a 
red-brown  color  and  indefinite  composition.  It  is  chiefly  used  for 
blacks  in  silk  dyeing,  and  for  iron-buff  on  cotton. 

Ferrous  nitrate  is  prepared  by  dissolving  iron  in  cold  dilute  nitr-ic 
acid  (1.10  sp.  gr.).  But  a  considerable  amount  of  ammonium  nitrate 
is  also  formed  in  the  solution,  according  to  the  reaction :  — 

4  Fe  +  10  HN03  =  4  Fe(N03)2  +  NH4N03  +  3  H20. 


NITRIC   ACID  123 

This  solution  is  very  unstable  and  decomposes  when  heated  even 
slightly,  forming  basic  ferric  nitrate  and  liberating  nitric  oxide. 

To  prepare  a  pure  ferrous  nitrate,  decomposition  of  a  ferrous 
sulphate  solution  by  barium  or  lead  nitrate  is  employed :  — 

FeS04  +  Ba(N03)2  =  BaS04  +  Fe(N03)2. 

The  solution  is  filtered  or  decanted  from  the  precipitated  barium 
sulphate. 

There  is  a  preparation  sold  as  "nitrate  of  iron,"  (probably  so 
called  because  some  nitric  acid  is  used  in  making  it),  which  is  not 
a  nitrate,  but  a  basic  ferric  sulphate  and  sulphate-nitrate  solution. 
A  solution  of  ferrous  sulphate  (copperas)  is  oxidized  by  nitric  acid, 
according  to  the  following  equations :  — 

1)  6  FeS04  +  2  HN03  +  2  H20  =  3  Fe2(S04)2 .  (OH),  +  2  NO. 

2)  6  FeS04  +  5  HN03  -  3  Fe2(S04)2 .  (N03)  •  (OH)  +  2  NO  +  H20. 

3)  6  FeS04  +  8  HN03  =  3  Fe2(S04)2  •  (N03)2  +  2  NO  +  4  H20. 

4)  12  FeS04  +  3  H2S04  +  4  HN03  =  3  Fe4(S04)5  •  (OH),  +  4  NO 

+  2  H20. 

Equation  4  gives  the  best  product. 

The  solution  of  basic  ferric  sulphate  and  sulphate-nitrates  is  a 
dark  brown-red  liquid,  and  is  much  used  in  silk  dyeing.  It  is  only 
mentioned  here  because  of  the  frequent  confusion  of  names  in  the 
commercial  article. 

Silver  nitrate  is  made  by  dissolving  the  metal  in  dilute  nitric 
acid :  — 

6  Ag  +  8  HN03  =  6  AgN03  +  4  H20  +  2  NO. 

If  the  silver  contains  copper,  the  resulting  solution  of  nitrates  is 
evaporated  to  dryness  and  then  heated  cautiously  to  about  250°  C., 
at  which  temperature  the  copper  nitrate  is  decomposed  into  copper 
oxide,  nitric  oxide,  and  oxygen,  while  the  silver  salt  is  not  altered. 
By  extracting  the  residue  with  water,  the  silver  nitrate  is  dissolved, 
leaving  the  copper  oxide.  The  solution  is  then  evaporated  to  crys- 
tallize the  silver  nitrate. 

The  salt  fuses  unchanged  at  225°  C.,  but  decomposes  if  heated 
nearly  to  redness ;  it  is  cast  in  small  sticks,  and  is  much  used  in 
medicine  for  a  cautery,  under  the  name  of  lunar  caustic. 

Silver  nitrate  has  a  very  corrosive  action  on  organic  matter.  It 
is  largely  used  in  photography,  and  to  a  lesser  degree  in  pharmacy, 
in  the  manufacture  of  mirrors,  in  preparing  "  indelible  inks,"  and  as 
a  chemical  reagent. 


124  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

Barium  nitrate  is  made  by  dissolving  the  native  carbonate 
(witherite)  in  hot,  dilute  nitric  acid;  or  it  may  be  prepared  by 
decomposing  a  concentrated  solution  (32°  Be.)  of  barium  chloride, 
by  the  addition  of  sodium  nitrate,  the  less  soluble  barium  nitrate 
precipitating.  The  salt  is  purified  by  recrystallization.  It  is  chiefly 
used  for  producing  "green  fire"  in  pyrotechnics  and  for  making 
barium  peroxide  (Ba02)  (p.  231).  It  is  also  used  as  an  oxidizing 
material  in  certain  explosives. 

Strontium  nitrate  is  made  by  dissolving  the  native  carbonate 
(strontianite)  in  hot  nitric  acid.  Its  chief  use  is  for  "  red  fire  "  in 
pyrotechnics. 

REFERENCES 

Berichte  iiber  die  Entwickelung  der  chemischen  Industrie,  u.  s.  w.     A.  "W. 

Hofmann,  1877.     (Vieweg,  Braunschweig.) 
Sulphuric  Acid  and  Alkali.     G.  Lunge.     Second  ed.,  Vol.  I.      (Gurney  and 

Jackson,  London.) 

The  Manufacture  of  Explosives.     Oscar  Guttmann.     (Nitric  acid  and  nitre.) 
Der  Chilisalpeter  und  Zukunft  der  Salpeterindustrie.     H.  Polakowsky.     Direct- 

orium  der  landwirthschaftl.    Hauptgenossenschaft  zu  Berlin.     Berlin,  1893. 
Zeitschrift  f.  angewandte  Chemie.     1893,  37.     Oscar  Guttmann. 
Journal  American  Chemical  Society,  1895,  576.    Edward  Hart. 
J.  Soc.   Chem.  Ind.,  1893,  128.      J.  Buchanan.     (Sodium  nitrate  in  Chile.) 

1893,  203.     Oscar  Guttmann.     (Nitric  acid.) 


AMMONIA 

Whenever  organic  matter  containing  nitrogen  is  submitted  to 
destructive  distillation,  more  or  less  ammonia  is  formed.  The  chief 
sources  of  ammonia  are  :  the  distillation  of  coal  for  gas  or  coke,  of 
bituminous  shales,  and  of  bones  and  other  animal  matter;  putrid 
urine  ;  the  residues  of  the  beet  sugar  industry  and  those  left  after 
the  fermentation  of  molasses  for  alcohol  ;  and  the  waste  gases  from 
blast  furnaces. 

Ammonia  can  be  made  from  the  nitrogen  of  the  air.  The  reac- 
tions involved  are  as  follows  :  — 


1)  Ba(OH)2  +  3C+2N  +  0  =  Ba(CN)2  +  H20  +  C02. 

2)  Ba  (ON),  +  4  H20  =  Ba  (OH),  +  2  CO  +  2  NH3. 

The  first  reaction  is  accomplished  by  passing  air  over  barium  hy- 
droxide or  oxide  and  carbon,  heated  to  a  white  heat.  Then  the 
temperature  is  lowered  to  about  450°  C.,  and  steam  admitted  to  de- 
compose the  barium  cyanide  according  to  (2).  The  reactions  are  not 
quantitative,  and  the  process  is  not  economical  and  is  unimportant. 


AMMONIA  125 

The  chief  source  of  ammonia  is  the  "gas  liquor"  from  the 
hydraulic  main  and  scrubbers  of  the  illuminating  gas  manufacture 
(p.  275).  The  nitrogen  contained  in  coal  is  largely  converted  into 
ammonia  and  cyanogen  compounds  by  destructive  distillation.  The 
principal  ammonium  salts  are  the  carbonate,  sulphide  and  sulphy- 
drate,  which  are  volatile  with  steam,  and  sulphate,  thiosulphate, 
sulphite,  sulphocyanide,  and  ferrocyanide,  which  are  not  volatile 
with  steam.  These  salts,  together  with  free  ammonia,  are  found 
in  the  "  gas  liquor."  Gas  liquor  is  valued  according  to  its  percent- 
age of  ammonium  salts,  as  determined  by  distilling  with  caustic 
soda,  absorbing  the  vapors  in  normal  sulphuric  acid  and  titrating 
the  uncombined  acid.  The  liquor  is  gauged  according  to  the  number 
of  ounces' of  concentrated  oil  of  vitriol  necessary  to  neutralize  one 
gallon  of  it ;  e.g.,  an  "  eight  ounce "  liquor  requires  eight  ounces  of 
oil  of  vitriol  to  combine  with  the  ammonia  from  one  gallon. 

More  or  less  tar  is  mixed  with  the  gas  liquor,  but  on  standing  this 
settles  to  the  bottom  of  the  tank.  The  clear  liquor  is  then  distilled 
to  separate  the  ammonia.  There  are  several  forms  of  apparatus  for 
this  distillation.  In  the  simplest  form  the  gas  liquor  is  heated  in 
one  still  until  all  the  volatile  salts  are  expelled,  and  then  it  is  drawn 
into  another  still,  where  "  milk  of  lime "  is  added,  and  heat  again 
applied  until  the  fixed  salts  are  decomposed  and  the  ammonia  driven 
off.  The  ammonia  and  volatile  salts  are  condensed  in  a  vessel  con- 
taining sulphuric  or  hydrochloric  acid.  Some  hydrogen  sulphide 
and  other  foul-smelling  gases  pass  out  of  the  absorption  vessel,  and 
are  led  into  the  chimney  or  are  decomposed  in  a  Glaus  kiln  (p.  85). 

In  England,  a  large  part  of  the  gas  liquor  is  distilled  in  Coffey 
stills  (p.  9),  but  since  it  is  inconvenient  to  use  lime  in  these  stills, 
most  of  the  fixed  salts  are  lost.  The  gas  liquor,  having  been  heated 
in  the  rectifier,  passes  into  the  analyzer,  and  there  the  volatile 
ammonia  salts  and  free  ammonia  are  driven  out  and  pass  through 
the  rectifier,  on  their  way  to  the  absorption  vessel. 

The  more  modern  apparatus  of  Feldmann  and  of  Grtineberg 
and  Blum,  are  now  much  used  on  the  continent  of  Europe  and  in 
America.  Feldmann's  apparatus  (Fig.  54)  is  most  used  in  this 
country.  The  gas  liquor  is  drawn  from  the  settling  tank  (F)  into 
the  economizer  (E),  which  consists  of  a  long,  cylindrical  shell,  con- 
taining a  number  of  narrow  tubes,  through  which  the  gas  liquor 
flows.  In  the  absorption  vessel  (D)  is  sulphuric  acid,  to  combine 
with  the  ammonia  vapors  passing  from  the  still  by  the  pipe  (G). 
The  hydrogen  sulphide  and  carbon  dioxide  liberated  in  (D)  are 
collected  under  the  bell.  The  heat  of  the  reaction  between  the  acid 


126 


OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


and  the  ammonia  raises  the  temperature  of  these  gases  to  a  high 
degree.  They  pass  through  the  outlet  pipe  into  the  outside  jacket 
or  shell  surrounding  the  tubes  in  the  economizer,  where  they  heat 
the  gas  liquor  which  is  flowing  through  the  small  tubes,  so  that  it  is 
hot  when  it  arrives  at  the  top  of  the  tower  (AB)  through  the  pipe 

(K).  In  the  tower,  the 
free  ammonia  and  its 
volatile  salts  are  driven 
out  by  the  steam  which 
is  passing  up  through  it. 
The  liquor  containing 
the  fixed  ammonia  salts 
then  passes  to  the  lower 
part  of  (AB),  where  it  is 
mixed  with  "milk  of 
lime "  while  steam  is 
blown  in.  The  mixture 
then  overflow^  through 
the  pipe  (M)  into  the 
smaller  still  (C),  where 
all  the  ammonia  set  free 
by  the  lime,  is  driven 
out  by  a  steam  jet  from 
(S).  This  ammonia 
passes  through  (ON)  in- 
to the  first  tower,  where 
it  mixes  with  the  gas 
escaping  from  (AB),  and 
is  absorbed  in  (D).  The  waste  liquors  escape  through  the  pipe  (P), 
and  the  sludge  of  calcium  salts  formed  in  ( B)  is  drawn  off  at  regular 
intervals  through  (R).  The  still  may  be  run  for  months  without 
stopping. 

The  Gruneberg-Blum  apparatus  is  rather,  more  complicated  in  its 
details,  but  involves  nearly  the  same  principles  as  the  above.  All 
the  stills  mentioned  here  employ  the  principle  of  dephlegmation 
(p.  8). 

An  appliance  for  distilling  gas  liquor  is  sometimes  employed  in 
which  the  vapors,  set  free  by  the  action  of  the  lime,  are  made  to 
bubble  through  fresh  gas  liquor  in  a  second  vessel.  Thus  the  vola- 
tile ammonia  salts  are  expelled  by  the  heat  of  these  vapors,  and 
pass  off  with  them  to  the  acid  absorption  tanks,  while  the  gas  liquor 
is  drawn  into  the  first  vessel  and  is  there  treated  with  lime.  This 


FIG.  54. 


AMMONIA  127 

method  was  used  in  the  old  apparatus  of  Griineberg  and  of  A. 
Mallet. 

The  ammonia  gas  set  free  in  any  of  the  above  described  stills  is 
generally  absorbed  in  sulphuric  acid.  If  dilute  acid  (80°  to  100°  Tw.) 
is  used,  there  is  no  separation  of  ammonium  sulphate  crystals  in 
the  saturator,  and  the  liquor  is  easily  clarified  from  tar  and  sus- 
pended impurities  before  evaporating  to  crystallize.  This  yields 
the  lightest  colored  product.  If  more  concentrated  acid  (140°  Tw.) 
is  used,  a  separation  of  ammonium  sulphate  crystals  takes  place  in 
the  saturator,  and  these  are  "fished  out."  But  they  are  often  dis- 
colored, since  the  liquor  has  had  no  chance  to  clarify  by  settling. 
As  fast  as  the  crystals  are  removed,  fresh  acid  is  introduced  in  a 
small  stream  into  the  saturator.  This  is  always  covered  with  a  lid, 
or  hood,  from  which  a  pipe  carries  off  the  foul  gases,  consisting 
largely  of  hydrogen  sulphide.  These  are  often  led  to  a  Glaus  kiln 
(p.  85)  and  decomposed  to  recover  the  sulphur,  thus  avoiding  con- 
tamination of  the  atmosphere.  A  recent  patent  *  involves  the  burn- 
ing of  this  gas  in  an  atmosphere  highly  impregnated  with  sulphur 
dioxide,  whereby  the  following  reaction  occurs :  — 

2  H.S  +  S02  =  2  H20  +  3  S. 

Care  is  taken  that  no  ammonia  passes  out  with  the  gases,  a  slight 
excess  of  acid  always  being  present.  The  ammonia  gas  is  led  into 
the  saturator  through  a  pipe  perforated  with  small  holes  and  sub- 
merged in  the  acid. 

Gas  liquor  is  not  always  distilled.  Occasionally  it  is  neutralized 
directly  with  mineral  acid  and  evaporated  to  dryness,  but  this  pro- 
duces a  salt  which  is  contaminated  with  tar,  while  the  escape  of 
hydrogen  sulphide  and  other  foul-smelling  gases  during  the  iieu- 
tralizating  is  liable  to  cause  nuisance.  Moreover,  the  solutions  thus 
obtained  are  dilute,  and  much  fuel  is  consumed  in  concentrating 
them. 

Ammonia  has  been  made  in  this  country  by  the  destructive  distil- 
lation of  waste  animal  matter  from  slaughter  houses  and  tanneries. 
Hair,  "fleshings"  from  tanneries,  scrap  leather,  etc.,  are  the  raw 
materials.  These  are  dried  and  put  into  an  upright  iron  cylinder, 
provided  with  a  manhole  at  the  top  and  at  the  bottom,  and  having  a 
large  perforated  pipe  running  up  through  the  centre,  about  three- 
fourths  of  the  distance  to  the  top.  Hot  chimney  gases  are  forced  by 
an  air  compressor  through  the  pipes  of  a  superheater  (a  furnace 
containing  coils  of  pipe  heated  to  a  bright  red  heat),  and  into  the 
*  J.  Soc.  Chem.  Ind.,  1897,  536  and  980. 


128  OUTLINES   OF  INDUSTRIAL   CHEMISTRY 

bottom  of  the  cylinder,  where  they  escape  through  the  perforated 
pipe,  and  come  into  direct  contact  with,  and  char,  the  animal  mai>- 
ter.*  The  volatile  products  of  the  heating  pass  out  at  the  top  of  the 
retort  into  a  hydraulic  main,  similar  to  those  used  in  gas  works. 
The  tarry  matter  settles  in  the  main,  and  the  gases  pass  through 
condensers,  which  are  cylinders  containing  4-inch  tubes.  Both  the 
condensed  liquors  and  the  gases  pass  into  absorption  tanks  contain- 
ing water.  The  unabsorbed  gases  pass  through  a  "scrubber,"  the 
same  as  that  used  for  gas  liquor,  to  remove  the  last  traces  of 
ammonia.  The  washed  gases  are  burned  under  the  retort.  The 
liquor  produced  in  the  absorbers  and  scrubbers  is  distilled  in  an 
ammonia  still,  Feldmann's  being  generally  used. 

The  coke  remaining  in  the  retort  is  porous,  and  contains  a  high 
percentage  of  nitrogen.  It  is  generally  used  for  fuel,  but  may  per- 
haps be  utilized  for  making  cyanides. 

Ammonium  sulphate,  as  found  in  commerce,  has  a  light  gray  or 
yellowish  color,  or,  if  carefully  made  and  washed  after  crystallizing, 
is  nearly  white.  When  prepared  by  direct  saturation  the  color  may 
be  brown  or  nearly  black.  Common  acid  made  from  pyrites  yields 
a  salt  which  is  yellow  in  color,  owing  to  the  iron  or  arsenic  present. 
The  crystals  should  be  washed,  and  dried  in  a  lead-lined  centrifugal 
machine.  It  is  sometimes  sold  damp,  but  is  generally  dried  by 
warm  air.  When  sold  in  large  quantities  it  is  always  valued  accord- 
ing to  its  content  of  ammonia  or  nitrogen.  Good  samples  contain 
from  23  to  25  per  cent  NH3.  It  is  largely  used  as  a  source  of  nitro- 
gen in  making  fertilizers,  but  for  this  purpose  must  be  free  from 
sulphocyanide,  which  is  very  injurious  to  vegetation.  When  made 
by  absorbing  the  gas  in  acid,  little  or  no  sulphocyanide  is  present, 
but  by  direct  neutralization  of  the  gas  liquor  the  cyanide  may  sepa- 
rate with  the  sulphate.  The  salt  is  used  as  a  source  of  other  ammo- 
nium compounds,  and  to  a  slight  extent  in  rendering  fabrics  and 
other  tissues  non-inflammable.  By  distilling  with  lime  it  yields  a 
very  pure  ammonia  gas,  which  may  be  absorbed  directly  in  water 
for  the  "  aqua  ammonia  "  of  trade ;  or  the  gas  may  be  passed  through 
towers  filled  with  charcoal,  to  remove  any  trace  of  tar,  before  ab- 
sorption. Any  sulphuretted  hydrogen  may  be  removed  by  passing 
the  gas  over  oxide  of  iron. 

A  considerable  amount  of  liquid  ammonia  is  now  prepared  and 
sent  into  the  market  for  use  in  ice  machines  (p.  19).  This  is  com- 
pressed into  steel  cylinders,  usually  containing  about  100  pounds  of 
the  liquid. 

*  It  is  said  that  the  process  did  not  prove  successful  in  practice  and  has  been 
given  up. 


AMMONIA  129 

Ammonium  chloride  is  made  by  absorbing  ammonia  gas  in  dilute 
hydrochloric  acid,  or  by  neutralizing  gas  liquor  with  the  acid  directly 
and  evaporating  the  solution.  During  the  evaporation  much  of  the 
tarry  matter  separates,  and  is  skimmed  off.  Some  nuisance  may 
result  from  the  gases  escaping  during  the  neutralizing. 

Another  method  is  to  mix  a  saturated  solution  of  ammonium 
sulphate  with  a  strong  solution  of  salt  or  potassium  chloride.  On 
evaporating  somewhat,  monohydrated  sodium  sulphate  (Na2S04  •  H20) 
separates  from  the  hot  liquor,  leaving  the  ammonium  chloride  in 
solution.  On  cooling,  the  ammonium  chloride  crystallizes  :  — 

(NH4)2S04 •-{-  2 NaCl  =  Na2S04  +  2 NH4CL 

The  crystallized  chloride  is  more  or  less  discolored  by  tar,  and 
is  purified  by  sublimation  (p.  10)  in  iron  or  earthenware  pots  or 
retorts.  The  ammonium  chloride  collects  on  the  cover  of  the  pot 
as  a  thick,  fibrous  cake,  in  which  form  it  comes  in  trade  under  the 
name  of  sal-ammoniac.  This  generally  contains  iron  as  an  impurity, 
It  was  formerly  made  by  subliming  the  soot  obtained  by  burning 
dried  camel's  dung,  but  is  now  nearly  all  made  from  gas  liquor. 
The  crystallized  salt  is  often  sold  under  the  name  of  "  muriate  of 
ammonia,'7  and  is  usually  less  pure  than  sal-ammoniac.  Muriate  of 
ammonia  is  much  used  in  the  arts  for  charging  Leclanche  electric 
batteries ;  in  the  process  of  "  galvanizing  "  iron ;  in  soldering  liquors ; 
for  making  "rust  cement"  for  pipe  joints;  and  in  textile  coloring. 

Ammonium  carbonate  as  found  in  commerce  is  not  a  pure  salt, 
but  is  a  mixture  of  acid  ammonium  carbonate  (NH4  •  HC03)  and  a 
salt  of  carbamic  acid  (NH2  •  C02  •  NH4).  The  commercial  salt  is 
made  by  heating  a  mixture  of  the  sulphate  and  powdered  calcium 
carbonate  in  iron  retorts.  The  vapors  are  condensed  in  lead-lined 
chambers,  and  the  impure  product  is  generally  sublimed  in  iron  pots 
having  lead  caps.  A  little  water  is  put  into  each  pot  along  with  the 
salt,  this  causing  the  sublimed  product  to  be  transparent  instead  of 
opaque  white.  The  temperature  of  this  second  sublimation  is  not 
much  above  70°  C. 

Ammonium  carbonate  is  transparent  when  fresh  and  pure,  but  on 
exposure  to  the  air,  becomes  covered  with  a  white  layer  of  bicarbon- 
ate, owing  to  the  loss  of  ammonia.  It  is  entirely  volatile  when 
heated,  and  from  this  fact  is  derived  its  old  name  of  sal-volatile.  It 
is  used  considerably  in  wool  scouring,  in  certain  baking  powders,  in 
medicine,  and  for  the  preparation  of  "  smelling  salts,7'  and  to  some 
extent,  as  an  analytical  reagent. 

Ammonium  sulphocyanide  (thiocyanate),  p.  248. 


130  OUTLINES  OF  INDUSTRIAL   CHEMISTRY 


REFERENCES 

Acetic  Acid,  Vinegar,  Ammonia,  and  Alum.  John  Gardner,  F.I.C.,  F.C.S., 
London,  1885.  (J.  and  A.  Churchill.) 

Chemie  des  Steinkohlentheers.  Dr.  Gustav  Schultz,  2te  Auf.,  Vol.  I,  Braun- 
schweig, 1886.  (Vieweg  und  Sohn.) 

Das  Ammoniak-Wasser.  Albert  Fehrmann,  Brauschweig,  1887.  (Vieweg  und 
Sohn.) 

Coal  Tar  and  Ammonia,  G.  Lunge,  2d  ed.,  London,  1887.    (Gurney  and  Jackson.) 

Ammoniak  und  Ammoniak-Praeparate.  Dr.  R.  Arnold,  Berlin,  1889.  (S. 
Fischer.) 

Traitement  des  Eaux  Arnmoniacales.  L.  Weill-Goetz  et  F.  Desor,  Strasbourg, 
1889.  (G.  Fischbach.) 


POTASH   INDUSTRY 

Previous  to  the  invention  of  the  Leblanc  Soda  Process,  the  most 
important  alkali  was  potassium  carbonate,  —  potash,  which  was 
nearly  all  derived  from  wood  ashes.  But  with  the  development  of 
the  soda  industry,  the  demand  for  potash  was  greatly  diminished, 
and  at  the  present  time,  soda  has  replaced  it  for  all  except  a  few 
special  purposes. 

The  chief  sources  of  potassium  salts  now  are :  — 

Wood  ashes. 

Beet-sugar  molasses  and  residues. 

Wool  scourings.     (Suint.) 

Stassfurt  salts. 

Land  plants  take  up  considerable  quantities  of  potassium  com- 
pounds from  the  soil.  When  the  plants  are  burned,  about  10  per 
cent  of  the  weight  of  the  ashes  is  potassium  carbonate,*  which  may 
be  obtained  by  lixiviation.  Potash  from  wood  ashes  is  now  chiefly 
made  in  Eussia,  Sweden,  and  America,  the  woods  most  employed 
being  elm,  maple,  and  birch.  Sometimes  the  stumps  and  small 
branches  only  are  burned,  the  trunks  being  used  for  timber.  The 
ashes  are  moistened  slightly,  put  into  tanks  having  false  bottoms  on 
which  straw  is  spread,  and  then  lixiviated  with  warm  water.  The 
lye  so  obtained  is  evaporated  (sometimes  by  the  waste  heat  from  the 
burning  wood)  in  iron  pots  until  it  solidifies  on  cooling.  The  dirty 
brown  mass  is  then  calcined  in  a  reverberatory  furnace  until  all  the 
organic  matter  is  destroyed.  The  product  is  known  as  potash  or 
crude  pearlash.  It  is  white  or  gray  in  color,  and  contains  about 

*  Those  plants  which  contain  much  silica  or  phosphoric  acid  —  straw  and  grasses 
—  yield  hut  little  potash. 


POTASH  INDUSTRY  131 

70  per  cent  K2C03,  with  some  sulphate  and  chloride  and  sodium  salts. 
By  redissolving  the  crude  potash  in  water,  settling  and  concentrat- 
ing the  solution  until  the  sulphates  and  chlorides  separate  as  crystals, 
a  concentrated  and  pure  lye  is  obtained.  When  this  is  evaporated 
to  dryness  and  the  residue  calcined,  it  yields  a  much  purer  product, 
known  as  "  refined  pearlash,"  and  containing  from  95  to  97  per  cent 
of  K2C03.  It  is  necessary  that  a  low  heat  be  employed  in  the  cal- 
cination, since  the  charge  fuses  at  a  moderate  temperature. 

Often,  some  quicklime  is  put  in  the  bottom  of  the  tanks  before 
the  ashes  are  introduced.  On  leaching,  the  solution  of  potassium 
salts  reacts  with  the  lime,  forming  insoluble  calcium  salts,  and  yield- 
ing more  or  less  potassium  hydroxide  in  the  lye.  The  resulting  prod- 
uct is  then  a  mixture  of  potash  and  caustic  potash. 

In  the  manufacture  of  beet  sugar,  a  very  impure  molasses  re- 
mains, containing  among  other  things  a  large  amount  of  soluble 
potassium  salts.  This  molasses  is  now  generally  fermented,  in 
which  process  the  sugary  substances  are  converted  into  alcohol, 
which  is  distilled  off,  leaving  the  mineral  salts  in  the  liquid  resi- 
due, called  vinasse  or  schlempe.  If  this  is  evaporated  to  dryness 
and  the  mass  calcined,  the  organic  potassium  salts  are  decomposed, 
leaving  in  the  cinder  about  35  per  cent  potassium  carbonate,  and  a 
large  amount  of  chloride  and  sulphate,  together  with  sodium  salts. 

If  the  vinasse  be  evaporated  to  dryness  and  the  residue  destruct- 
ively distilled  in  retorts,  a  distillate  is  obtained,  containing  organic 
compounds  of  which  methyl  alcohol  CH3OH,  ammonia,  and  tri- 

/CH3 
methylamine,  ]ST  —  CH3  are  valuable.     The  cinder  in  the  retort  con- 

\CH3 

tains  potassium  salts,  which  are  obtained  in  solution  by  lixiviation, 
and  a  considerable  quantity  of  potash  is  thus  recovered.  Very  often, 
however,  the  ash  is  used  as  a  fertilizer,  thus  returning  the  potash 
to  the  soil. 

Wool  scourings  furnish  some  potash  in  countries  where  much 
wool  is  washed.  Sheep's  wool  as  it  comes  from  the  animal  contains 
from  30  to  75  per  cent  of  its  weight  of  impurities,  consisting  of 
dirt,  sand,  dung,  etc. ;  wool  grease  or  "  yolk,"  a  fat-like  substance, 
made  up  of  cholesterine  and  compounds  of  it  with  oleic,  stearic,  and 
palmitic  acids ;  and  "  suint"  which  consists  chiefly  of  potassium 
salts  of  oleic,  stearic,  and  other  organic  acids,  with  small  quantities 
of  chlorides  and  sulphates  and  nitrogenous  matter.  The  "  suint " 
exudes  from  the  animal  in  the  perspiration,  and  is  deposited  on  the 
wool  by  evaporation.  It  is  soluble  in  cold  water,  and  is  thus  removed 


132  OUTLINES  OF  INDUSTRIAL   CHEMISTRY 

in  the  scouring  process.  If  these  wash  waters,  containing  wool 
grease  and  suint,  are  run  into  the  drains  or  streams,  pollution  of  the 
water  results.  The  prevention  of  this  nuisance,  as  well  as  the  value 
of  the  potash,  has  necessitated  attempts  to  dispose  of  the  washings 
in  some  economical  manner,  and  they  are  usually  evaporated  to  dry- 
ness  and  calcined.  If  the  calcination  is  done  in  closed  retorts,  a 
considerable  quantity  of  ammonia  is  obtained.  The  cinder  is  lixiv- 
iated, and  on  evaporation,  the  solution  yields,  first,  chlorides  and 
sulphates  of  potassium  and  sodium,  and  finally  a  very  pure  potash, 
which  averages  a  little  less  than  4  per  cent  of  the  weight  of  the  raw 
wool  scoured. 

For  the  recovery  and  treatment  of  wool  grease,  see  pp.  320  and 
444. 

This  utilization  of  wool  grease  and  suint  is  mainly  practised  in 
France,  Belgium,  and  Germany,  and  in  these  countries  this  is  done 
chiefly  to  prevent  the  pollution  of  the  streams.  Cheap  fuel  is  very 
essential  to  a  successful  working  of  the  process.  On  a  small  scale 
it  cannot  be  carried  on  profitably,  and  the  wash  waters  are  often  run 
onto  the  fields  as  fertilizer. 

For  potassium  carbonate  from  potassium  chloride,  see  p.  135. 

By  far  the  most  important  source  of  potassium  compounds  at  the 
present  time  is  the  great  natural  deposit  of  potassium  salts  found 
at  Stassfurt  and  Leopoldshall,  near  Magdeburg,  Germany.  This 
consists  of  immense  beds  of  various  salts,  which  have  been  deposited 
from  sea  water.  They  were  discovered  in  attempting  to  reach  the 
underlying  rock-salt,  but  because  of  the  large  proportion  of  potas- 
sium and  magnesium  chlorides,  the  material  was  at  first  thrown 
aside  as  worthless,  the  name  applied  to  it,  —  "  abmumsalze"  —  indi- 
cating the  small  value  attached  to  it.  But  in  1861-4  methods  were 
devised  by  which  potassium  chloride  and  sulphate  could  be  obtained 
cheaply  from  the  Stassfurt  salts,  and  since  these  furnish  a  valu- 
able source  for  nearly  all  other  potassium  salts,  a  rapid  development 
of  the  industry  followed. 

Sea  water  contains  about  3.5  per  cent  of  solids,  consisting  of :  — 

Sodium  chloride 76.49  per  cent* 

Magnesium  chloride 10.20  «« 

Magnesium  sulphate 6.51  " 

Calcium  sulphate 3.97  " 

Potassium  chloride 1.98  " 

Magnesium  bromide *     '     *  1  0  85  " 

Calcium  bicarbonate,  etc j 

*  Regnault  (Thorpe's  Dictionary  of  Applied  Chemistry,  Vol.  Ill,  266). 


POTASH  INDUSTRY  133 

By  the  evaporation  of  sea  water  under  certain  conditions,  these 
salts,  together  with  various  doable  salts,  formed  by  mutual  inter- 
reactions,  crystallize  in  the  order  of  their  relative  insolubility. 

The  Stassfurt  deposit  was  undoubtedly  formed  by  the  evaporation 
of  sea  water,  under  peculiar  conditions.  The  mode  of  formation  has 
been  studied  by  many  investigators,  to  whose  memoirs  the  reader  is 
referred  for  full  explanations.*  The  deposit  is  nearly  3000  feet  thick, 
and  about  16  different  salts  have  been  identified  in  the  various  strata. 
The  more  important  salts  and  their  composition,  are  given  below:  — 

Gypsum  ........  CaSO4.2H2O 

Anhydrite    .......  CaS04 

Kainite    ........  K2S04,  MgS04,  MgCl2-6H20 

Carnallite     .......  KC1,  MgCl2  •  6  H2O 

Kieserite  ........  MgS04-H2O 

Polyhalite    .......  K2SO4,  MgS04,  2  CaSO4  •  2  H20 

Kock-Salt     .......  NaCl 

Sylvine    ........  KC1 

Tachydrite    .......  CaCl2,  2  MgCl2  •  12  H20 

Boracite  ........  2  (Mg3B8Oi5)  +  MgCl2 

Astrakanite  .......  MgS04,  Na2S04  •  4  H2O 

Schoenite      .......  K2S04,  MgS04  •  6  H2O 

The  beds  are  not  sharply  defined  layers  of  separate  salts,  the  de- 
posit being  generally  regarded  as  containing  four  principal  "regions." 

The  rock-salt  or  anhydrite  region  is  the  lowest  of  these.  This 
consists  of  thin  layers  of  very  pure  rock-salt,  separated  by  narrow 
strata  (one-fourth  of  an  inch  thick)  of  anhydrite.  The  anhydrite  is 
separated  from  the  salt  mechanically,  and  the  latter  is  then  ground 
for  use  directly.  This  bed  is  nearly  2000  feet  thick  in  places. 

The  polyhalite  region,  about  200  feet  thick,  is  above  the  rock- 
salt  region.  It  is  composed  of  91  per  cent  of  rock-salt,  and  6|-  per 
cent  of  polyhalite,  with  smaller  quantities  of  other  salts. 

The  kieserite  region,  lying  next  above,  is  about  185  feet  thick, 
and  contains  65  per  cent  rock-salt,  17  per  cent  of  kieserite,  13  per 
cent  carnallite,  and  5  per  cent  of  other  salts. 

The  carnallite  region  lies  nearest  the  surface,  and  is  about  140 
feet  thick.  This  is  the  most  important  and  contains  :  — 

Carnallite      ...........    .     55-60  per  cent 

Rock-salt  ........    .....    20-25  per  cent 

Kieserite  .............     16  per  cent 


...........      4  per  cent 

Boracite     / 

*  A  very  good  account  is  given  in  Thorpe's  Dictionary  of  Applied  Chemistry,  Vol. 
Ill,  pp.  266-268.    Also  see  Pfeiffer's  Handbuch  der  Kali-Industrie. 


I 

Potassium  chloride    .     .     . 

16.2  per  cent 

Magnesium  chloride  .     .     . 

24.3 

t 

Sodium  chloride     .... 

18.7 

' 

Calcium  chloride    .... 

0.2 

t 

Magnesium  sulphate  .     .     . 

9.7 

• 

Calcium  sulphate  .... 

2.1 

i 

Water      .                         .     . 

28.8 

i 

Insoluble 

00.0 

, 

134  OUTLINES   OF  INDUSTRIAL   CHEMISTRY 

In  parts  of  this  region,  changes  have  taken  place  through  the 
action  of  water,  by  which  considerable  deposits  of  kainite  and 
sylvine  have  been  formed.  The  composition  of  raw  carnallite  is 
about  as  follows  :  — 

II 

>  .  15.7  per  cent 
.  *  21.3  " 
.  .  21.5  " 
.  .  0.3  " 
,  .  13.0  " 
.  .  00.0  " 
.  .  26.2  " 
.  .  2.0  » 

The  crude  carnallite  is  often  colored  a  deep  red  by  the  presence 
of  iron  compounds. 

The  present  commercial  supply  of  potassium  chloride,  and  inci- 
dentally of  other  potassium  compounds,  is  obtained  from  carnallite. 
The  crude  material  is  treated  with  the  hot  mother -liquor  from  a 
previous  lot,  in  an  iron  kettle  having  a  stirring  apparatus  and  a  false 
bottom.  This  mother-liquor  contains  about  20  per  cent  MgCl2,  which 
prevents  the  solution  of  the  rock-salt  and  kieserite,  but  does  not 
hinder  the  dissolving  of  the  carnallite.  The  action  of  the  magnesium 
chloride  solution  is  continued  until  the  hot  liquor  reaches  a  density 
of  1.32  sp.  gr.,  when  it  is  drawn  off  from  the  sludge  and  allowed  to 
cool  slowly.  At  this  density,  the  greater  part  of  the  potassium 
chloride  crystallizes  on  cooling,  leaving  the  magnesium  chloride  and 
some  potassium  chloride  still  in  solution.  This  liquor  is  then 
further  concentrated,  until  it  contains  about  30  per  cent  mag- 
nesium chloride.  On  cooling,  crystals  having  the  composition 
KC1,  MgCl2  •  6  H20,  —  artificial  carnallite,  —  separate,  leaving  only 
the  excess  of  magnesium  chloride  in  solution.  The  artificial  carnal- 
lite  is  decomposed  with  water,  and  the  potassium  chloride  crystallized 
out,  leaving  the  magnesium  chloride  in  solution;  a  part  of  this 
liquor,  diluted  with  the  wash  water  from  the  sludge,  is  used  to 
extract  the  next  portion  of  raw  carnallite.  The  potassium  chloride 
is  washed  with  a  small  portion  of  very  cold  water,  to  remove  the 
common  salt. 

The  residue  from  the  solution  of  the  raw  carnallite  consists 
largely  of  kieserite  mud  (MgS04  •  H.,0),  which  is  insoluble  in  water ; 
but  on  standing  for  some  time  in  contact  with  water,  it  passes  over 
into  the  soluble  Epsom  salts  (MgS04  •  7  H20).  At  an  intermediate 
stage  of  the  hydration,  the  mud  solidifies  in  a  manner  similar  to 


POTASH   INDUSTRY  135 

plaster  of  Paris  when  mixed  with,  water.  When  this  solidification 
is  about  to  take  place,  the  mud  is  moulded  into  blocks,  which  become 
very  hard,  and  in  which  form  it  is  shipped.  But  after  some  time 
they  take  up  moisture  from  the  air,  and  fall  to  a  powder  of  Epsom 
salt. 

Glauber's  salt  is  made  at  Stassfurt  in  the  winter  time  as  fol- 
lows :  Solutions  of  common  salt  and  magnesium  sulphate  (e.g. 
from  kieserite)  when  kept  below  0°  C.  will  react  together,  thus :  — 

MgS04  +  2  NaCl  =  MgCl2  +  Na2S04, 

and  at  the  low  temperature,  the  sodium  sulphate  crystallizes  to  form 
Na2S04  •  10  H20. 

Kainite  (K2S04,  MgS04,  MgCl2  -  6  H20)  is  extensively  used  in  the 
crude  state  as  a  fertilizer.  Some  of  it,  however,  is  treated  for 
potassium  sulphate,  by  the  method  of  H.  Precht.  When  heated 
with  water  under  pressures  of  four  or  five  atmospheres,  kainite 
decomposes  into  a  double  potassium-magnesium  sulphate,  magne- 
sium chloride,  and  potassium  chloride,  thus :  — 


+  2  KC1  + 16  H20. 


3  (K2S04,  MgS04,  MgCl2 .  6  H20) 

=  2  (K2S04,  2  MgS04  •  H20)  +  2  MgCl 

The  double  potassium-magnesium  sulphate  separates  in  crystals, 
and  is  freed  from  chlorides  by  washing ;  during  the  washing,  one 
molecule  of  the  magnesium  sulphate  is  also  removed,  and  a  salt 
of  the  composition,  K2S04,  MgS04,  remains.  This  is  dried  and 
calcined,  and  sold  as  double  potassium-magnesium  sulphate;  or  it 
may  be  decomposed  directly  by  treating  with  a  solution  of  potas- 
sium chloride  of  1.142  sp.  gr. :  — 

K2S04,  MgS04  +  2  KC1  =  MgCl2  +  2  K2S04. 

The  potassium  sulphate  is  separated  from  the  magnesium,  chlo- 
ride by  crystallization. 

Potassium  sulphate,  made  from,  kainite  as  above,  or  by  the 
action  of  sulphuric  acid  on  potassium  chloride,  is  largely  used  as 
a  fertilizer  and  for  the  manufacture  of  potassium  carbonate. 

Potassium  chloride,  chiefly  obtained  from  carnallite,  is  exten- 
sively used  for  preparing  other  potassium  salts,  especially  the 
nitrate  (p.  121),  sulphate,  and  carbonate. 

Potassium  carbonate  or  potash  is  made  from  potassium  chloride 
by  the  Leblanc  process,  in  the  same  way  as  soda-ash  from  salt.  But 
the  ammonia  process  cannot  be  employed,  because  the  acid  carbonate 


136  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

of  potassium  (KHS04)  is  soluble  in  ammoniacal  solutions,  and  does 
not  precipitate. 

Potassium  carbonate  is  sold  in  trade  under  the  name  of  potash 
or  pearlash,  and  is  used  chiefly  in  the  glass  industry,  for  caustic 
potash  and  for  chromates  of  potassium.  A  considerable  quantity  is 
bought  by  soap  makers,  and  causticized,  the  solution  being  used  for 
soft  soaps  (p.  322). 

Caustic  Potash  is  made  in  the  same  way  as  caustic  soda  (p.  80). 
The  mother-liquors  from  the  black-ash  lixiviation  are  decomposed 
directly  with  slaked  lime.  Caustic  potash  is  much  more  deliques- 
cent than  caustic  soda,  and  is  generally  made  where  it  is  to  be  used. 

In  soap  making,  it  was  formerly  customary  to  saponify  the  fat 
with  caustic  potash,  and  then  to  add  common  salt.  An  interchange 
between  the  potassium  and  sodium  took  place,  and  a  hard  sodium 
soap  resulted.  But  as  soda  is  now  cheaper,  and  yields  a  hard  soap 
directly,  potash  soaps  are  only  used  for  special  purposes. 

Potassium  nitrate.     (See  p.  120.) 

Potassium  bichromate  (K2Cr207)  is  made  by  roasting  chromite  (a 
native  oxide  of  chromium  and  iron)  with  potash,  lixiviating  the 
fused  mass  with  water,  and  adding  enough  sulphuric  acid  to  convert 
the  neutral  potassium  chromate  into  bichromate.  The  reactions 
involved  are  as  follows :  — 

Cr203-f-30==2Cr03; 

Cr03  +  K2C03  =  K2Cr04  +  C02 ; 

2  K2Cr04  +  H2S04  =  K2S04  +  K2Cr207  +  H20. 

The  finely  powdered  chrome  ore  is  mixed  with  lime  and  potash, 
and  roasted  at  a  bright  red  heat,  with  free  access  of  air  and  frequent 
stirring.  After  several  hours  the  chromic  oxide  is  all  oxidized  to 
chromium  trioxide  (Cr03),  which  combines  with  the  lime  and  pot- 
ash to  form  neutral  chromates  of  calcium  and  potassium.  The  mass 
is  then  treated  with  a  hot  solution  of  potassium  sulphate,  which 
forms  potassium  chromate  from  the  calcium  chromate.  The  solu- 
tion of  neutral  potassium  chromate,  when  saturated,  is  drawn  off 
and  settled.  It  is  then  decomposed  in  lead-lined  tanks,  by  the  addi- 
tion of  sulphuric  acid.  Since  potassium  bichromate  is  very  much 
less  soluble  in  cold  solution  than  the  neutral  chromate,  about  three- 
fourths  of  the  total  amount  of  bichromate  formed  precipitates.  The 
remaining  liquor,  containing  potassium  sulphate,  is  used  to  leach 
a  new  portion  of  cinder.  The  precipitated  bichromate  is  recrystal- 
lized  from  water. 


FERTILIZERS  137 

The  addition  of  lime  to  the  furnace  charge  is  necessary  to  pre- 
vent the  fusion  of  the  mass,  and  to  keep  it  porous,  so  that  the 
oxidation  of  the  chrome  is  more  complete. 

Potassium  bichromate  is  much  used  as  a  source  of  other  chromium 
compounds;  as  an  oxidizing  agent  in  dyeing  and  making  coal-tar 
dyes ;  as  a  mordant ;  as  a  bleaching  agent  for  oils  and  fats ;  and  for 
the  preparation  of  leather  in  the  chrome  tannage  processes. 

REFERENCES 

Die  Industrie  von  Stassfurt  u.  Leopoldshall.    G.  Krause.     Coethen,  1877. 

Handbuch  der  Kali  Industrie.     E.  Pfeiffer,  1887. 

Die  Salz  Industrie  von  Stassfurt.     Dr.  Precht,  Stassfurt,  1889.     (R.  Weicke.) 

Die  Stassfurter  Kali-Industrie.     G.  Lierke,  Wien,  1891.     (Hilschmann.) 

J.  Soc.  Chern.  Ind.,  1883,  146,  C.  N.  Hake. 

Chemische  Zeitung,  1890,  Grief.     1891,  Heyer. 

Dingler's  polyteclmisches  Jour.    Vol.  241.     Precht. 


FERTILIZERS 

Growing  plants  are  nourished  by  certain  constituents  which  they 
absorb  from  the  soil  and  air.  The  chief  elements  drawn  from  the 
soil  are  potassium,  calcium,  sulphur,  phosphorus,  and  nitrogen; 
other  elements  such  as  silicon,  iron,  sodium,  magnesium,  and  chlorine 
are  taken  up  to  a  less  degree.  The  natural  weathering  of  the  min- 
erals in  the  ground  usually  provide  the  elements  necessary  to  plant 
life;  but  the  supply  of  potassium,  phosphorus,  and  nitrogen  may 
be  insufficient  and  become  exhausted  by  frequent  repetitions  of  the 
same  crops  on  the  same  land.  The  soil  becomes  less  productive,  and 
finally  the  crops  are  failures. 

To  supply  this  continued  drain  on  the  soil,  fertilizers  are  employed. 
The  natural  fertilizers,  barn-yard  manure,  urine,  and  decomposing 
vegetable  mould  or  muck,  will  not  be  considered  here,  as  they  need 
little  or  no  treatment  before  use. 

By  artificial  fertilizers  we  understand  those  manurial  substances, 
prepared  from  materials  which  need  some  special  treatment  to 
render  them  fit  for  plant  food.  The  chief  requisites  of  a  good  arti- 
ficial fertilizer  are :  — 

1.  It  must  contain  at  least  one  substance  fit  for  plant  food,  and 
this  substance  must  be  easily  convertible,  by  the  action  of  rain  and 
moisture,  to  such  a  form  that  plants  can  assimilate  it. 

2.  It  must  be  dry  and  finely  powdered,  so  that  it  may  be  evenly 
distributed  over  the  surface  of  the  ground. 


138  OUTLINES   OF  INDUSTRIAL   CHEMISTRY 

3.  It  must  contain  nothing  injurious  to  plant  life. 

4.  It  must  be  cheap. 

A  complete  fertilizer  should  supply  the  three  essentials,  potas- 
sium, nitrogen  and  phosphorus.  But  the  majority  of  artificial 
fertilizers  afford  only  one  or  two  of  these  elements,  and  are  usually 
sold  for  certain  crops,  or  for  use  on  particular  kinds  of  soil. 

Potassium  is  generally  returned  to  the  soil  in  the  form  of  sul- 
phate or  carbonate  (wood  ashes),  and  occasionally  as  chloride.  The 
preparation  and  use  of  these  salts  have  already  been  considered  and 
also  the  preparation  of  ground  kainite  (p.  135)  for  this  purpose. 

Nitrogen  is  frequently  supplied  as  ammonium  salts  (p.  128),  or 
nitrates,  particularly  sodium  nitrate  (p.  119).  But  many  substances 
used  for  fertilizers  contain  nitrogen  in  organic  compounds,  which 
decompose  readily  in  the  soil,  setting  free  the  nitrogen. 

Phosphorus  is  nearly  always  applied  to  the  soil  in  some  form  of 
calcium  phosphate  derived  from  mineral  sources  or  from  organic 
matter.  The  most  important  branch  of  the  fertilizer  industry  is 
the  preparation  of  phosphates. 

Fertilizers  are  largely  made  from  the  waste  products  of  slaughter 
houses,  such  as  blood,  bits  of  waste  meat  and  other  refuse,  bones, 
hoofs,  horns,  and  hair.  Tainted  meat  and  animals  which  have  died 
of  disease  are  also  sent  to  the  rendering  tanks.*  Blood  is  dried  at  a 
moderate  heat  and  crushed  to  powder  between  rolls.  It  contains 
about  10  per  cent  1ST,  and  is  very  uniform  in  composition. 

Bones  are  very  good  fertilizing  material,  supplying  both  nitrogen 
and  phosphorus  when  used  as  raw  bone ;  i.e.  without  treatment 
other  .than  grinding.  But  as  a  rule  the  bones  are  extracted  with 
benzine  and  then  boiled,  or  extracted  with  steam  under  pressure  to 
remove  the  fats  and  gelatine  (p.  527),  after  which  the  residue  is 
ground  and  used  directly  for  fertilizer  as  bone  meal,  the  fineness 
of  this  "  meal "  having  much  influence  on  the  rapidity  of  its  decay 
in  the  soil.  Being  more  spongy  and  soft,  it  yields  its  phosphoric 
acid  in  a  much  shorter  time  than  the  hard  "  raw  bone.'7  The  latter 
contains  about  22  per  cent  of  phosphoric  acid  and  4  per  cent  of 
nitrogen.  But  steaming  reduces  the  nitrogen  to  about  1  per  cent, 
while  the  proportion  of  phosphoric  acid  is  raised  to  27  or  28  per  cent. 

Bones  are  often  subjected  to  destructive  distillation  in  retorts, 
by  which  nearly  all  the  nitrogen  is  driven  out  as  ammonia,  ammo- 
nium carbonate,  pyridine,  and  other  nitrogenous  organic  compounds, 

*  "Rendering"  consists  in  extracting  all  the  fats,  oils,  and  gelatinous  matter  from 
the  carcasses  by  treating  with  benzine  or  steam  under  pressure.  The  fat  extracted 
is  used  for  soap  stock.  ' '  » 


FERTILIZERS 


139 


while  the  residue  left  in  the  retort,  known  as  "  bone-char  "  or  "  bone- 
black,"  contains  calcium  phosphates  and  other  salts,  mixed  with 
carbon.  This  bone-char  is  extensively  used  as  a  decolorizing  agent 
in  the  purification  of  sugar,  glucose,  oils,  and  other  liquids ;  when  it 
can  no  longer  be  employed  for  this  purpose  (see  p.  265)  it  is  burned 
with  free  access  of  air  to  form  "white-ash,"  which  contains  a  high 
percentage  of  phosphorus.  This  bone-ash  may  be  used  directly  as  a 
fertilizer,  but  is  usually  treated  with  sulphuric  acid  to  form  "  super- 
phosphate" (p.  143),  which  is  more  soluble  than  the  tricalcium 
phosphate  of  the  bone. 

A  process  for  extracting  the  mineral  phosphate  from  bones  by 
digesting  with  hydrochloric  acid  has  been  practised  to  some  extent. 
The  solution  of  phosphoric  acid  thus  obtained  is  neutralized  with 
milk  of  lime,  by  which  the  calcium  phosphate  is  precipitated,  chiefly 
as  dicalcium  phosphate  (Ca2H2P208).  This  is  sometimes  sold  as 
"  precipitated  phosphate,"  but  the  method  is  more  commonly  applied 
to  low  grades  of  mineral  phosphates  (p.  145)  than  to  bones. 

Garbage  containing  fatty  matter  is  now  collected  in  many  cities 
and  subjected  to  a  rendering  process.  It  is  put  into  steel  digesters 
and  subjected  to  the  action  of  steam  at  50  pounds  pressure  for  eight 
or  ten  hours,  when  the  mass  is  reduced  to  a  soft  pulp  which  is  put  into 
presses  and  the  oily  matter  pressed  out.  The  press-cake  is  broken 
up  and  dried  in  revolving  steam-heated  drums,  after  which  it  is 
powdered,  sifted,  and  used  for  "  filler  "  in  fertilizers,  under  the  name 
"tankage."  It  contains  nitrogen,  phosphoric  acid,  and  a  little 
potash.  On  cooling  the  oily  matter  forms  a  soft  grease,  which  is 
used  for  soap  and  candle  stock.  The  water  which  is  pressed  out  of 
the  tankage  with  the  grease  contains  a  large  amount  of  ammonium 
salts  and  some  potash ;  it  is  evaporated  to  dryness  and  the  residue 
mixed  with  the  tankage,  thus  increasing  the  nitrogen  and  potash  in 
the  latter. 

Other  nitrogenous  waste  from  various  industries  —  leather  scrap, 
wool  waste  and  dust  from  shoddy  and  felt  mills  —  are  used  to  some 
extent;  but  these,  though  very  rich  in  nitrogen,  are  very  slow  in 
decomposing,  and  are  so  light  when  powdered  that  they  are  easily 
blown  away. 

The  press-cakes  from  various  oil  industries  (e.g.  the  manufacture 
of  cotton-seed,  rape,  and  castor  oils)  are  often  ground  for  fertilizer. 
Sometimes  the  cake  is  burned  for  fuel  and  the  ashes  used  for  fertiliz- 
ing, but  in  this  case  the  nitrogen  is  lost,  only  the  potassium  and 
phosphorus  being  returned  to  the  soil.  In  the  manufacture  of  fish 
oils  there  is  a  considerable  amount  of  residue  from  which  the  oil  has 


140  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

been  pressed.  This  is  known  as  "  fish  scrap,"  and  consists  of  the 
scales,  bones,  fins,  and  meat  of  the  fish.  It  contains  about  7  per 
cent  of  nitrogen  and  nearly  16  per  cent  of  phosphorus  pentoxide 
(P20B).  It  is  dried  (usually  by  exposure  to  the  sun)  and  then 
crushed  to  a  rather  coarse  powder.  It  is  a  valuable  fertilizer, 
decaying  rapidly  in  the  soil  and  feeding  the  plants  continually. 

Peruvian  guano  was  formerly  of  great  importance  as  a  fertilizer, 
but  now  the  beds  are  nearly  exhausted.  It  consists  of  dried  excre- 
ment, feathers,  and  carcasses  of  sea  fowl,  and  is  rich  in  nitrogen  and 
phosphoric  acid.  It  is  found  in  certain  islands  near  the  coast  of 
Peru  and  Chili,  and  also  on  the  mainland  at  the  base  of  the  Andes, 
near  the  sodium  nitrate  beds  (p.  119).  The  region  is  dry  and  hot, 
and  the  guana  has  been  thus  preserved  with  a  high  percentage  of 
nitrogen,  largely  as  uric  acid  and  its  salts.  It  needs  no  preliminary 
treatment  before  spreading  on  the  soil. 

Fresh  guano,  collected  yearly  from  various  islands  in  the  South 
Pacific,  is  damp,  and  contains  a  large  amount  of  ammonium  carbon- 
ate ;  this  must  be  "fixed"  by  mixing  with  sulphuric  acid,  to  prevent 
loss  of  the  nitrogen. 

Fossil  guanos,  consisting  of  fossil  excrement  and  remains  of  birds 
and  reptiles,  are  found  in  the  West  Indies,  Bolivia,  Chili,  and  the 
South  Pacific  islands.  Since  more  or  less  rain  falls  in  these  climates, 
the  soluble  ammonium  salts  and  nitrates  have  been  washed  out, 
leaving  only  the  calcium  phosphate.  Some  of  these  guanos  have 
entered  into  combination  with  the  rocks  on  which  they  were  de- 
posited, thus  altering  their  original  character  considerably ;  e.g.  some 
of  them  contain  a  large  amount  of  calcium  sulphate.  Fossil  guanos 
are  prepared  in  the  same  way  as  phosphate  rock.  (See  below.) 

The  largest  source  of  phosphoric  acid  ,is  now  phosphate  rock, 
especially  apatite  and  phosphorite.  These  are  found  in  large  deposits 
in  Belgium,  Germany,  France,  Spain,  Algiers,  Canada,  South  Caro- 
lina, Florida,  and  the  West  Indies.  At  present  the  United  States 
deposits  are  the  most  important. 

Apatite  [3  Ca3P208  +  CaF2  •  (CaCl2)]  is  a  crystalline  mineral, 
occurring  in  large  deposits  in  Canada  and  Spain.  The  former  are 
very  extensive,  and  are  found  in  Ontario,  between  the  St.  Lawrence 
and  Ottawa  rivers,  and  in  Quebec  Province,  along  the  Gatineau  and 
du  Lievre  rivers.  The  mineral  sometimes  occurs  in  veins  and 
pockets  (bonanzas)  of  nearly  pure,  massive  apatite ;  and  in  other 
cases  as  distinct,  hexagonal  crystals  or  nodules,  disseminated  in 
calcite  or  pyroxene.  The  material  is  sold  on  a  guarantee  of  75  or 


FERTILIZERS  141 

80  per  cent  of  calcium  phosphate,  and  to  secure  this  degree  of  purity, 
'•cobbing"*  and  hand-picking  must  be  employed.  The  ore  being 
exceedingly  brittle  and  the  gangue  rock  very  hard,  there  is  much 
loss  in  the  "fines,"  from  which  it  is  not  profitable  to  separate  the 
phosphate  rock. 

Apatite  varies  in  character  from  a  moderately  hard  rock,  to  a  soft 
and  friable  mass,  called  "sugar."  The  color  varies  much,  but  is 
generally  blue-green  or  red-brown.  The  tricalcium  phosphate  being 
quite  insoluble,  the  mineral  must  be  treated  with  sulphuric  acid  to 
form  "superphosphate."  But  since  more  or  less  calcium  fluoride 
and  chloride  is  present,  considerable  acid  is  uselessly  consumed,  and 
a  special  condensing  apparatus  is  necessary  to  retain  the  vapors  of 
hydrofluoric  and  hydrochloric  acids  set  free,  or  a  nuisance  is  created. 
Apatite  also  requires  a  rather  strong  acid  (1.78  sp.  gr.)  for  its  decom- 
position, while  the  calcite  and  other  minerals  connected  with  it  being 
acted  upon,  cause  considerable  loss  of  acid. 

These  objections  do  not  apply  to  the  phosphorites  of  the  United 
States  and  Europe,  and  the  cost  of  mining  is  not  so  great.  As  a 
result  the  Canadian  mines  are  now  nearly  all  closed^  and  there  seems 
little  probability  that  they  will  be  opened  for  many  years  to  come. 

Phosphorites  are  amorphous  rocks  of  varying  composition,  but  all 
containing  a  large  percentage  of  tricalcium  phosphate,  and  some- 
times iron  and  aluminum  phosphates.  The  mode  of  formation  of 
these  rocks  has  been  a  much-disputed  question,  but  they  are  now 
generally  regarded  as  of  organic,  and  probably  animal  origin.  The 
beds  are  filled  with  fossil  remains  of  land  and  marine  animals  and 
fishes.  A  nodular  variety  found  in  England  was  erroneously  sup- 
posed to  be  fossil  reptilian  excrement,  and  was  called  "  Coprolites." 

Some  phosphorites  are  compact  and  hard  to  grind,  as  is  the 
Spanish  variety,  but  the  American  rock  is  softer  and  porous.  In 
the  United  States  there  are  two  varieties,  "  land  rock  "  and  "  river 
rock." 

Land  rock  occurs  in  beds  averaging  from  10  to  12  inches  in  thick- 
ness, and  from  2  to  40  feet  below  the  surface  of  the  ground.  These 
beds  are  sometimes  composed  of  loose  pebbles  or  gravel,  but  fre- 
quently these  have  been  compacted  into  solid  layers  having  a  lami- 
nated structure;  or  they  may  form  great  boulders  or  conglomerate 
masses.  The  beds  are  often  continuous  over  a  large  area,  but 
"pockets"  or  isolated  beds  are  frequently  found.  Good  rock  will 
average  from  75  to  80  per  cent  of  tricalcium  phosphate  (Ca3P208). 
In  some  cases  the  land  rock  is  hard,  dense,  and  nearly  pure  (hard 
*  Breaking  the  large  lumps  with  hammers  by  hand. 


142  OUTLINES  OF  INDUSTRIAL   CHEMISTRY 

phosphate),  while  in  others  it  is  soft,  resembling  clay  in  its  consist- 
ency, and  usually  containing  rather  a  large  proportion  of  iron  and 
aluminum. 

Land  rock  is  mined  by  stripping  off  the  overlying  earth,  and 
digging  out  the  phosphate  rock  with  pick  and  shovel.  It  has  been 
found  practical  to  use  steam  shovels  and  dredges  for  "soft  phos- 
phate "  and  "  pebble  "  deposits.  In  compact  rock,  blasting  is  neces- 
sary. The  work  is  done  in  open  pits,  tunnelling  not  having  proved 
successful.  The  depth  of  overburden  which  may  be  profitably 
removed,  depends  upon  the  thickness  and  purity  of  the  deposit,  but 
about  20  feet  is  the  limit,  except  in  the  case  of  very  thick  beds  of 
high  grade  ore.  For  ordinary  rock,  the  limit  is  about  10  or  12  feet. 
In  a  few  cases  hydraulic  mining  has  been  employed  to  wash  away 
the  overburden. 

After  mining,  the  rock  is  put  through  a  "breaker,"  and  reduced 
to  lumps  about  4  inches  in  diameter.  These  go  to  the  "washer" 
which  consists  of  a  long,  semicircular  trough,  set  at  a  slight  incline, 
in  which  there  is  a  revolving  shaft,  carrying  teeth  or  blades  about 
9  inches  long,  and  arranged  around  it  in  the  form  of  a  spiral 
screw,  having  a  pitch  of  about  1  in  6.  The  trough  is  set  in  a 
tank  of  water,  or  a  large  stream  of  water  enters  at  the  upper  end. 
The  lumps  of  rock  are  fed  into  the  trough  at  the  lower  end,  and 
being  caught  by  the  teeth,  are  forced  along  and  up  the  trough, 
against  the  water.  The  rubbing  against  each  other,  and  the  action 
of  the  water,  washes  away  the  sand  and  clay,  and  at  the  upper  end 
the  clean  rock  falls  on  screens,  which  separate  the  several  sizes  of 
lumps.  It  is  usually  dried  by  piling  it  on  racks  of  cord  wood,  which 
are  then  fired  and  allowed  to  burn  out ;  or  it  may  be  piled  over  cast- 
iron  pipes  having  numerous  apertures,  and  through  which  hot  air 
from  a  furnace  is  forced.  The  rock  is  then  shipped  to  the  makers 
of  "  superphosphate." 

Eiver  rock  is  dredged  or  dug  from  the  beds  of  rivers  and  streams, 
especially  Peace  Eiver  and  its  tributaries  in  Florida,  and  from  the 
streams  near  Charleston  and  Beaufort,  S.C.  When  the  deposit 
is  in  the  form  of  loose  nodules  and  gravel,  steam  dredges  or  cen- 
trifugal pumps  are  used  to  raise  it;  but  when  it  is  compact  rock, 
special  forms  of  grips  and  dredges  are  necessary.  In  most  cases, 
river  mining  is  not  carried  on  in  water  more  than  30  feet  deep. 

River  rock  is  very  similar  in  composition  to  land  rock,  but  is 
darker  in  color,  even  black,  and  contains  more  animal  remains  and 
fossils.  Jt  is  preferred  by  foreign  superphosphate  makers  and  is 
generally  shipped  abroad. 


FERTILIZERS  143 

"  Superphosphate  "  is  the  name  given  to  a  soluble  phosphate,  pre- 
pared by  treating  insoluble  rock  or  bone  *  phosphate,  with  sulphuric 
acid.  By  the  action  of  the  sulphuric  acid,  the  insoluble  tricalcium 
phosphate  is  converted  into  monocalciiim  phosphate  (CaH4P208), 
while  in  many  cases  some  free  phosphoric  acid  is  also  formed. 

The  reactions  involved  are  as  follows  :  — 


A+  2  H2S04+6H20  =  (CaH4P208+2  H20)  +2(CaS04  -  2  H20). 

2)  Ca3PA+3  H2S04+6  HaO=2  H3P04+3(CaS04  .  2  H20). 

3)  Ca3PA+H2S04+  6  H.O^Ca^PA  -  4  H20)  +  (CaS04  -  2H,0). 

Reactions  1  and  2  are  the  ones  desired  in  fertilizer  making,  but 
if  too  little  acid  is  used,  reaction  3  takes  place  to  a  greater  or  less 
extent,  forming  some  dicalcium  phosphate,  which  is  also  insoluble. 
If  too  much  acid  is  used,  reaction  2  takes  place  to  an  undesirable 
extent,  and  the  product  contains  an  excess  of  free  phosphoric  acid, 
which  attracts  moisture  from  the  air,  making  the  fertilizer  moist 
and  lumpy.  A  small  excess  of  sulphuric  acid  over  the  theoretical 
quantity  needed  is  generally  used  to  prevent  "reversion"  (p.  144) 
as  far  as  possible.  The  proper  regulation  of  the  amount  of  acid 
is  a  matter  of  great  care,  and  must  be  controlled  by  analysis  of  the 
material.  The  acid  employed  is  "chamber  acid"  of  1.54  to  1.60 
sp.  gr.  Concentrated  acid  is  not  used,  because  water  is  necessary 
in  order  that  a  hydrated  calcium  sulphate  as  well  as  a  hydrated 
monocalciiim  phosphate  may  be  formed.  The  formation  of  the 
gypsum  (CaS04  •  2  H20)  greatly  assists  in  the  subsequent  drying  of 
the  product. 

Hydrochloric  acid  is  unsuitable  for  fertilizer  making,  because  of 
its  expense,  and  the  formation  of  calcium  chloride  in  the  product. 
The  raw  phosphate  should  be  as  free  as  possible  from  impurities, 
such  as  carbonates,  iron  oxide  and  alumina.  About  3  per  cent  of 
Fe  A  +  A1203  is  the  limit  now  allowed. 

The  phosphate  rock,  powdered  to  pass  an  80-mesh  sieve,  is  put  into 
a  lead-lined  mixer,  provided  with  effective  stirring  apparatus,  and 
the  required  amount  of  acid  is  added.  The  mixing  is  complete  in 
two  or  three  minutes,  and  then  the  liquid  charge  is  at  once  run  into 
a  brick-lined  "  pit,"  where  the  principal  reactions  take  place.  The 
temperature  rises  very  rapidly  to  100°  or  110°  C.,  and  a  great  quantity 
of  gases  (HC1,  HF,  CO2,  and  SiF4)  escape  through  the  draught  flue. 
As  the  reaction  progresses,  the  mass  becomes  stiff  and  finally  solidi- 
fies, forming  a  single  cake,  which  is  broken  up,  removed  from  the 

*  Superphosphate  made  from  bones  contains  some  nitrogen  as  well  as  phosphoric 
acid. 


144  OUTLINES  OF  INDUSTRIAL   CHEMISTRY 

pit,  and  dried  by  steam  heat,  at  a  temperature  of  105°  C.  The  mass 
is  then  powdered  in  a  "disintegrator  mill." 

Frequently  the  superphosphate  is  mixed  with  nitrogenous  or 
potash  materials  in  the  disintegrator,  to  furnish  a  "  complete "  fer- 
tilizer. It  is  then  packed  in  bags  and  is  ready  for  market. 

If  the  phosphate  rock  contains  much  iron  or  aluminum  oxide,  or 
if  the  decomposition  by  acid  has  been  incomplete,  a  series  of  sec- 
ondary reactions  ensues,  when  the  superphosphate  is  stored.  By 
these,  a  part  or  all  of  the  monocalcium  phosphate  (CaH4P208),  and 
the  free  phosphoric  acid  may  be  converted  into  the  insoluble  di- 
calcium  phosphate,  or  into  insoluble  phosphates  of  iron  or  aluminum. 
This  constitutes  what  is  called  "  reversion,"  and  the  insoluble  calcium 
or  iron  phosphates  so  formed  are  called  "reverted  phosphate." 
Since  fertilizer  is  usually  valued  according  to  its  percentage  of  soluble 
phosphate,  reversion  is  a  serious  matter  for  manufacturer  and  buyer. 
Reverted  phosphate  is  recognized  as  having  a  certain  value  for 
fertilizer  purposes,  but  much  less  than  superphosphate. 

When  due  to  incomplete  decomposition  of  the  rock,  reversion 
takes  place  according  to  the  following  reaction :  — 

CaH4P208  +  Ca3P2O8  =  2  Ca2H2P208. 

When  the  rock  contains  iron  or  alumina,  the  temperature  of  the 
reaction  in  the  pit  is  kept  as  low  as  possible,  to  prevent  combina- 
tion between  these  oxides  and  the  free  phosphoric  acid  formed.  It 
is  customary  in  this  case  to  remove  the  superphosphate  from  the  pit 
as  soon  as  it  solidifies,  and  to  cool  it  by  exposure  to  the  air. 

A  "  double  superphosphate  "  is  also  made,  especially  in  Europe, 
and  contains  more  soluble  phosphoric  acid  than  the  ordinary 
superphosphate.  A  certain  quantity  of  bones  or  phosphate  rock  is 
decomposed  with  sufficient  dilute  sulphuric  acid  to  set  free  all  the 
phosphoric  acid  and  precipitate  all  the  calcium  as  hydrated  calcium 
sulphate.  The  precipitate  is  then  filtered  off  by  means  of  the  filter 
press  (p.  12),  and  the  clear  solution  of  phosphoric  acid  is  concen- 
trated by  surface  heating  in  lead  pans,  to  a  density  of  45°  Be.,  at 
which  strength  the  solution  contains  nearly  45  per  cent  P205.  Dur- 
ing this  concentration,  the  iron  and  aluminum  phosphates  separate 
and  are  removed.  The  strong  solution  of  phosphoric  acid  is  then 
treated  with  ground  phosphate  rock,  in  proper  quantity  to  form 
monocalcium  phosphate,  which  is  dried  and  disintegrated.  The 
reactions  involved  are  as  follows  :  — 

1)  Ca3P208  +  3  H2S04  +  6  H20  =  3  (CaS04  •  2  H20)  +  2  H3PO<. 

2)  Ca3P208  +  4  H3P04  4-  6  H20  =  3  (CaH4P A  +  2  H.O). 


FERTILIZERS 


145 


By  this  process,  a  very  concentrated  fertilizer,  containing  no 
gypsum  or  other  sulphate,  is  obtained.  Moreover,  a  low-grade  phos- 
phate rock  can  be  used  for  making  the  phosphoric  acid,  which  would 
not  furnish  a  strong  fertilizer  with  sulphuric  acid. 

A  small  amount  of  phosphate  rock  is  used  directly  for  fertilizer, 
without  other  preparation  than  fine  grinding.  But  tricalcium  phos- 
phate, being  very  insoluble,  is  only  slowly  assimilated  by  plants,  and 
its  action  is  not  very  marked.  Several  years  are  necessary  for  its 
complete  decomposition. 

Phosphatic  slag  is  now  used  to  a  considerable  extent  as  a  fertil- 
izer, especially  in  Europe.  In  the  process  of  making  Bessemer  steel 
by  the  Thomas  and  Gilchrist  method,  pig  iron  from  ores  containing 
phosphorus  is  treated  with  an  excess  of  lime  in  a  Bessemer  con- 
verter, lined  with  lime,  while  a  blast  of  air  is  forced  into  the  liquid 
mass.  At  the  high  temperature  of  the  melted  iron,  the  phosphorus 
is  oxidized  to  pentoxide,  which  combines  with  the  lime.  The  silica, 
alumina,  lime,  and  magnesia  unite  to  form  a  slag,  into  which  the 
calcium  phosphate  produced  also  goes.  By  proper  regulation  of  the 
charge,  a  slag  containing  about  17  per  cent  of  pentoxide  (P205)  is 
obtained.  The  phosphate  in  the  slag  is  supposed  to  be  a  tetracalcic 
phosphate  (Ca4P209),  which  is  insoluble  in  water,  but  is  much  less 
stable  than  tricalcium  phosphate.  When  exposed  to  the  weather  in 
the  soil,  it  decomposes,  though  somewhat  slowly,  and  the  phosphorus 
passes  into  a  form  which  plants  can  assimilate.  In  order  that  this 
decomposition  may  take  place,  the  slag  must  be  ground  very  fine,  so 
that  90  per  cent  of  it  will  pass  through  a  sieve  with  100  meshes  to 


FIG.  55. 


the  linear  inch.  The  grinding  is  best  done  in  a  ball  mill  (Fig.  55), 
which  consists  of  a  cast-iron  drum  (D),  and  containing  numerous 
chilled  iron  or  steel  balls  (B)  of  different  sizes.  The  coarsely  ground 


146  OUTLINES  OF  INDUSTRIAL   CHEMISTRY 

slag  is  powdered  by  the  rubbing  and  pounding  of  the  balls  as  the 
drum  rotates.  It  then  passes  through  the  perforated  plates  (P)  and 
falls  on  fine  brass  sieves  (S).  The  coarser  particles,  which  cannot 
pass  through  the  sieves,  return  to  the  interior  of  the  drum,  through 
the  openings  (C,  C),  for  further  grinding. 

Slag  fertilizer  needs  no  further  treatment  than  very  fine  grind- 
ing, but  it  is  slow  in  decomposing,  and  its  full  effect  is  not  obtained 
for  two  or  three  years.  It  decomposes  more  rapidly  than  ground 
phosphate  rock,  however,  and  is  cheap. 

There  has  been  considerable  controversy  among  agricultural 
chemists  as  to  the  relative  value  of  soluble  and  insoluble  phos- 
phates. Some  hold  that  the  soluble  phosphate  is  at  once  converted 
into  the  insoluble  form  when  it  comes  into  contact  with  the  lime, 
alumina  and  iron  in  the  soil;  and  that  this  insoluble  phosphate  is 
dissolved  or  absorbed  by  the  sap  in  the  plant  roots,  the  sap  pre- 
sumably having  an  acid  nature.  Other  chemists  claim  that  only  the 
soluble  phosphate,  as  such,  can  be  taken  up  by  the  plant.  It  ap- 
pears from  observed  facts,  however,  that  both  soluble  and  insoluble 
phosphates  are  taken  up  by  the  plant,  but  the  nature  of  the  soil  is 
an  important  factor.  On  a  soil  poor  in  lime,  and  containing  some 
organic  matter,  insoluble  phosphates  produce  their  best  results ;  but 
if  the  soil  contains  much  lime,  then  the  superphosphate  appears  to 
have  the  advantage. 

The  soluble  character  of  the  superphosphate  permits  its  dif- 
fusion through  the  soil  by  rain,  so  that  it  is  brought  immediately 
to  the  roots  of  the  plants.  But  the  insoluble  phosphate  must  be 
turned  under  the  soil,  and  the  roots  grow  to  it ;  then,  too,  when  not 
finely  ground,  it  possesses  but  little  value,  owing  to  the  slow  decom- 
position ;  but  when  in  a  very  fine  powder  it  is  taken  up  in  some  way 
by  the  roots  of  the  plant  with  fair  rapidity. 

The  manufacture  and  sale  of  artificial  fertilizers  are,  to  a  certain 
extent,  under  legal  restriction  in  nearly  all  the  states.  To  prevent 
fraud,  manufacturers  are  required  to  take  out  a  license,  and  to-  sub- 
mit samples  for  analysis  by  state  chemists ;  frequently  a  guarantee 
of  the  stated  composition  is  required.  The  methods  of  analyses  of 
fertilizers  are  set  forth  in  detail  in  the  bulletins  of  the  several 
state  agricultural  experiment  stations  and  of  the  United  States  De- 
partment of  Agriculture.*  In  general  the  matter  determined  by  the 
analysis  may  be  summed  up  as :  — 

(a)    Water,  both  hygroscopic  and  combined. 
*  Bull.  No.  28,  U.  S.  Dept.  Agriculture;  Division  of  Chemistry. 


FERTILIZERS  147 

(6)  Total  phosphoric  acid. 

(c)  Soluble  phosphoric  acid. 

(d)  Reverted  phosphoric  acid. 

(e)  Total  nitrogen. 
(/)  Potash. 

Another  substance  frequently  sold  as  fertilizer  is  pulverized 
gypsum  (CaS04  •  2  H20),  which,  when  crushed  to  a  fine  powder,  is 
brought  into  commerce  under  the  name  of  "plaster."  As  a  fertil- 
izer it  is  of  little  value,  except  in  soils  poor  in  lime  or  those  contain- 
ing "  black  alkali "  (sodium  carbonate).  But  it  is  also  claimed  to 
have  a  beneficial  action  in  retaining  nitrogen  in  the  soil.  The 
calcium  sulphate  is  supposed  to  be  decomposed  by  the  ammonia  and 
carbonic  acid  from  the  air  and  rain,  forming  ammonium  sulphate 
and  calcium  carbonate.  Ammonium  sulphate  furnishes  nitrogen  in 
a  form  which  plants  can  assimilate. 

Much  attention  has  been  devoted,  especially  in  Germany,  to 
methods  of  recovering  fertilizing  material  from  the  sewage  of  cities. 
But  when  closets  are  flushed  with  water,  the  effluent  is  generally  too 
dilute  to  be  worth  recovering.  It  is,  however,  used  to  some  extent, 
in  irrigating  lands,  generally  those  owned  by  the  municipality. 
Sewage  is  often  precipitated  with  lime  or  other  substance,  but  this 
generally  renders  the  sludge  useless  for  fertilizing.  The  contents  of 
dry  vaults  or  cesspools  are  collected  at  regular  intervals  and  used 
for  fertilizing. 

But  sewage  treatment  of  any  kind  is  usually  practised  to  pre- 
vent pollution  and  unsanitary  conditions  in  the  streams  and  water 
supplies,  rather  than  for  the  utilization  of  the  fertilizing  materials 
to  be  obtained. 

REFERENCES 

Lehrbuch  der  Diingerfabrication.     Paul  Wagner.     Braunschweig,  1877. 

Report  of  the  Commissioner  of  Agriculture  of  South  Carolina,  for  the  year 
1880.  Chas.  U.  Shepard. 

Bulletin  de  la  Socie'te'  Chimique,  1834,  219.     E.  Dreyfus. 

Die  kunstlichen  Diingermittel.     Dr.  S.  Pick,  Leipzig,  1887.     (Hartleben.) 

The  Nature  and  Origin  of  Deposits  of  Phosphate  of  Lime.  R.  A.  F.  Penrose, 
Bull.  46,  U.S.  Geological  Survey,  Washington,  1888. 

A  Treatise  on  Manures.     A.  B.  Griffiths,  London,  1889.     (Geo.  Bell  and  Sons.) 

The  Phosphates  of  America.  Francis  Wyatt,  New  York,  1891.  (Scientific 
Publishing  Co.) 

Florida,  South  Carolina,  and  Canadian  Phosphates.  C.  C.  Hoyer  Millar,  Lon- 
don, 1892.  (Fischer  and  Co.) 

Les  Phosphates  de  Chaux  naturels.     Paul  Hubert,  Paris,  1893. 


148  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

The  Phosphate  Industry  of  the  United  States.     Carroll  D.  Wright,  Washington, 

1893.     (Sixth  Special  Report  of  the  U.S.  Commissioner  of  Labor.) 
J.  Amer.  Chem.  Soc.,  1893,  321.     Chas.  U.  Shepard.     1895,  47.     W.  E.  Gar- 

rigues. 
J.  Soc.  Chem.  Ind.,  1888,  79.     W.  T.  MacAdam.     1894,  842.     Kalmann  and 

Meissels. 
Agricultural  Analysis.     F.  W.  Wiley,  Vol.  II,  Fertilizers,  Easton,  Penn.,  1896. 

(Chemical  Publishing  Co.) 


LIME,  CEMENT,  AND   PLASTER   OF   PARIS 

Good  lirne  is  nearly  pure  calcium  oxide  ;  it  is  one  of  the  most 
important  substances  used  in  chemical  industry,  and  is  prepared  in 
enormous  quantities  by  calcining  calcium  carbonate  at  a  bright  red 
heat.  If  the  carbonate  used  (limestone,  chalk,  or  the  shells  of  mol- 
lusks)  contains  much  silica,  iron,  alumina,  or  other  impurity,  the 
lime  does  not  slake  freely  with  water,  and  is  said  to  be  "  poor  "  or 
"lean."  If  but  small  quantities  of  these  impurities  are  present,  a 
fair  lime  is  produced,  when  properly  burned.  But  such  impure 
carbonates  are  very  difficult  to  burn,  since  slight  overheating  causes 
semi-fusion  of  the  lumps,  and  the  lime  combines  with  water  very 
slowly  and  incompletely,  and  is  said  to  be  "burned  to  death."  A 
pure  lime,  which  combines  readily  with  water  to  form  a  fine  white 
powder,  free  from  grit,  and  which  makes  a  smooth  stiff  paste  with 
an  excess  of  water,  is  called  a  "  fat "  lime. 

Calcium  carbonate  begins  to  decompose  below  a  red  heat  into 
calcium  oxide  and  carbon  dioxide,  but  the  decomposition  is  not 
complete  until  a  bright  red  heat  (800°  or  900°  C.)  is  reached.  The 
temperature  should  not  rise  much  above  1000°  to  1200°  C. ;  as  there 
is  danger  of  overheating  the  lime.  For  successful  burning,  it  is 
essential  that  the  gases  escape  freely  from  the  kiln,  the  draught 
usually  being  sufficient  to  remove  them  as  they  form.  This  escape 
may  be  accelerated  by  blowing  steam  or  air  into  the  kiln  during  the 
burning,  or  even  by  wetting  the  carbonate  as  it  is  introduced.  If 
the  gases  are  retained,  they  cause  pressure  in  the  kiln  and  thus 
hinder  the  decomposition;  and  on  cooling,  the  carbonic  acid  re- 
combines  with  the  lime. 

There  are  two  general  classes  of  limekilns,  continuous  and 
periodic.  (See  Calcination,  p.  18.)  The  former  are  preferred 
where  fuel  is  expensive,  and  where  a  large  regular  output  is  desired. 
They  are  tall,  narrow  furnaces  (shaft  kilns),  built  of  brick  or  of  iron 
plates,  and  vary  much  in  size,  but  are  usually  from  40  to  45  feet 


LIME,   CEMENT,   AND   PLASTER  OF  PARIS 


149 


high,  by  7  feet  in  diameter.     The  carbonate  is  fed  in  at  the  top  and 

the  linie  taken  out  at  the  bottom,  without  interrupting  the  process. 

Figure  56  shows  a  furnace  for 

burning     with     "long    flame." 

The  fuel  is  burned  on  the  grate 
(A),  and  only  the  flames  and 

combustion  gases  pass  through 

(B)  to  come  in  contact  with  the 

charge  in  the  shaft.     The  ashes 

fall  into  the  chamber  (D),  and 

are   thus   kept    separate    from 

the  lime,  which  is  withdrawn 

through  (C)  at  regular  intervals, 

causing  a  slow  descent  of  the 

charge.     Thus  a  clean  lime  is 

obtained. 

In     the     continuous     kilns 

which  use  the  "short  flame,"  FlG  56 

the    carbonate    and    fuel    are 

charged   alternately  at   the   top,  and  the  lime,  contaminated  with 

ashes,  is  taken  out  at  the  bottom.     Less  fuel  is  needed  than  for 

"long  flame  burning." 

Fuel  gas  for  lime  burning  has  been  successfully  introduced  in 

many  places.     This  gives  a  very  clean  lime,  burned  at  a  constant 

temperature. 

In  this  country,  long-flame, 
periodic  kilns  are  generally  used. 
These  require  much  fuel  and 
time,  but  are  probably  preferred 
because  of  the  simplicity  and 
cheapness  of  building.  They  are 
made  of  brick  or  of  large  blocks 
of  limestone.  Two  or  three  feet 
from  the  ground  an  arch  (A) 
(Fig.  57),  of  large  blocks  of  lime- 
stone, is  turned,  numerous  small 
openings  being  left,  through 
which  the  flames  niay  pass  into 
the  interior  of  the  kiln.  The 

fire  is  built  under  the  arch,  and  on  top  of  the  latter  the  limestone  is 

piled,  the  lumps  varying  in  size  from  that  of  a  cocoanut,  just  above 

the  arch,  to  that  of  a  goose  egg  at  the  top  of  the  kiln.     When  the 


FIG.  5T. 


150  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

kiln  is  full,  the  fire  is  started  and  the  temperature  very  slowly  raised 
during  six  or  eight  hours,  to  prevent  the  limestone  arch  from  crum- 
bling ;  then  the  temperature  is  kept  at  a  full  red  heat  for  two  days 
or  more,  when  the  fire  is  allowed  to  burn  out,  and  the  kiln  cools. 
During  the  time  of  cooling,  discharging,  and  recharging,  the  kiln 
stands  idle,  and  thus  much  time  is  lost.  Moreover,  a  large  amount 
of  fuel  is  necessary  to  heat  the  walls  of  the  kiln  after  each  re- 
charging, so  that  the  method  is  not  an  economical  one. 

Excepting  the  limekilns  in  the  ammonia-soda  works,  no  attempt 
is  made  in  this  country,  to  save  the  carbonic  acid  gas  which  escapes 
from  the  top  of  the  kiln.  But  in  Europe  the  gas  is  often  collected 
and  used  for  technical  purposes. 

Freshly  burned  lime  is  usually  called  "  caustic  "  lime  or  "  quick- 
lime," because  of  its  corrosive  action  on  organic  matter.  When 
pure,  it  is  white  and  amorphous,  but  iron  gives  it  a  yellow  or  brown 
color.  The  crystalline  limestones  and  pure  marble  yield  the  best 
lime.  Owing  to  the  loss  of  water,  organic  matter,  and  carbon  dioxide 
during  the  burning,  there  is  great  reduction  in  the  weight  of  the 
charge,  but  only  a  slight  decrease  in  its  volume.  As  a  rule,  100 
pounds  of  good  limestone  yield  about  57-59  pounds  of  lime,  but  the 
shrinkage  in  bulk  is  not  over  10-15  per  cent  of  the  original  volume 
of  the  limestone.  Nor  is  there  much  change  in  the  hardness,  though 
lime  is  much  more  porous  than  the  limestone,  and  absorbs  consider- 
able water  before  slaking. 

Pure  lime  is  infusible  at  the  temperature  of  the  oxy-hydrogen 
flame  (hence  its  use  in  the  "  calcium  light "),  but  if  silica,  iron, 
alumina  or  other  substance  is  present,  the  lime  combines  with  it  to 
form  a  fusible  substance  (glass  or  slag).  Considered  chemically, 
lime  is  calcium  oxide,  and  is  a  powerful  base.  It  combines  with  acids 
to  form  calcium  salts ;  it  has  great  affinity  for  water,  and  when  wet 
the  lumps  expand  and  fall  to  a  powder  of  calcium  hydroxide  (slaked 
lime),  with  the  evolution  of  much  heat,  especially  in  the  case  of  "  fat 
lime."  When  exposed  to  the  air  lime  absorbs  carbon  dioxide  and 
moisture,  and  soon  falls  to  a  powder  called  "  air  slaked  lime,"  consist- 
ing of  a  mixture  of  calcium  carbonate  and  hydroxide.  Lime  for  mor- 
tar and  many  other  purposes  is  always  slaked  immediately  before 
use. 

If  the  limestone  contains  more  than  from  8  to  10  per  cent  of  sili- 
cate of  aluminum  (clay),  and  is  burned  at  a  moderate  temperature, 
"  hydraulic  lime "  is  obtained.  This  does  not  slake  freely,  and  if 
kept  in  contact  with  water  after  slaking  it  soon  hardens  again.  This 
hardening  is  due  to  a  secondary  reaction  between  the  water  and  the 


LIME,   CEMENT,   AND  PLASTER  OF  PARIS  151 

anhydrous  silicates  and  aluminates  of  calcium,  which  have  been 
formed  in  the  burning,  and  which  combine  with  the  water  to  form 
hydrated  compounds,  having  considerable  hardness.  Hydraulic 
limes  are  chiefly  employed  in  mortar  and  cement  mixtures. 

Since  much  heat  is  liberated  in  the  slaking  of  lime,  the  storage 
and  shipment  is  attended  with  some  danger.  If  water  comes  into 
contact  with  the  lime  in  presence  of  combustible  material,  fire  is 
very  apt  to  ensue. 

The  uses  of  lime  in  the  arts  are  too  numerous  for  extended  men- 
tion, but  the  following  are  a  few  of  the  most  important :  in  mortar 
and  cement  mixing  ;  in  bleaching  powder ;  in  the  Leblanc  soda  pro- 
cess ;  for  purifying  illuminating  gas ;  in  the  preparation  and  purifi- 
cation of  many  chemicals,  such  as  acetic,  citric,  oxalic,  and  tartaric 
acids,  potassium  chlorate,  caustic  soda  and  potash,  etc. ;  for  purify- 
ing sugar  solutions ;  in  bleaching  and  dyeing  cotton ;  in  tanning ;  in 
glass  making ;  in  metallurgical  operations ;  for  disinfecting,  etc. 

Mortar  is  an  aqueous  pasty  mixture  of  slaked  lime,  sand,  and 
other  materials,  which  dries  without  excessive  shrinkage  and  be- 
comes hard  on  exposure  to  the  air,  owing  to  absorption  of  carbon 
dioxide  and  formation  of  carbonate  of  lime.  It  will  not  harden 
while  it  remains  wet,  and  this  is  one  of  the  chief  differences  be- 
tween mortar  and  cement.  The  hardening  of  the  two  substances  is 
due,  in  part  at  least,  to  different  causes. 

If  a  paste  of  freshly  slaked  lime  is  allowed  to  dry  by  exposure  to 
the  air,  it  shrinks  considerably,  and  if  in  thick  masses,  numerous 
cracks  are  formed.  The  admixture  of  three  or  four  volumes  of  sharp 
sand  prevents  this  shrinkage  by  separating  the  lime  paste  into  very 
thin  layers,  which  fill  the  spaces  between  the  grains  of  sand.  The 
sand  also  gives  the  mortar  a  porous  structure,  which  facilitates  the 
penetration  of  the  carbon  dioxide  during  the  hardening  period.  The 
interlacing  crystals  of  calcium  carbonate  enclose  the  sand  grains  and 
join  them  together,  thus  increasing  the  hardness  and  strength  of  the 
mortar.  This  addition  of  sand  also  cheapens  the  mortar  by  increas- 
ing the  mass  obtained  from  a  given  amount  of  lime.  "Fat  lime" 
requires  a  much  larger  proportion,  which  is  replaced  in  part  by  the 
impurities  in  "  poor  "  lime. 

For  a  good  mortar  it  is  very  necessary  that  the  lime  be  thoroughly 
slaked.  The  proper  quantity  of  water  should  be  added  all  at  once, 
or  the  product  is  apt  to  be  granular  and  lumpy.  The  mass  is  cov- 
ered with  a  layer  of  sand,  or  with  boards  or  canvas,  to  retain  the 
heat  and  moisture,  and  should  not  be  stirred  while  slaking,  but 
should  be  allowed  to  swell  and  fall  to  powder  without  disturbance. 


152  OUTLINES   OF  INDUSTRIAL   CHEMISTRY 

Water  is  then  added,  and  the  paste  allowed  to  stand  for  several  days, 
or  even  weeks,  well  protected  from  the  air,  before  being  stirred  up 
with  more  water  for  use  in  mortar. 

The  first  change  noticeable  in  a  mortar  is  the  "  set,"  which  is  a 
solidification  of  the  mass,  due  to  the  loss  of  its  water  through  evapo- 
ration or  absorption  by  the  bricks,  etc.  But  it  is  not  until  after  the 
mass  becomes  dry  that  the  real  hardening  begins.  This  is  very  slow, 
since  it  progresses  from  without  towards  the  interior  of  the  mass ; 
and  the  surface  layer  of  calcium  carbonate  first  formed  is  but  slowly 
penetrated  by  carbon  dioxide  from  the  air.  The  interior  of  thick 
walls  will  often  show  an  alkaline  reaction  after  the  lapse  of  a  century 
or  two,  but  after  twenty-five  years  the  change  is  very  slight  under 
ordinary  conditions.  After  several  hundred  years  there  appears  to 
be  a  certain  amount  of  combination  between  the  silica  of  the  sand 
and  the  calcium  carbonate  to  form  a  hydrated  silicate  of  calcium. 
This  secondary  reaction  does  not  increase  the  hardness  of  the  mor- 
tar. Hardening  is  a  true  chemical  change,  and  should  not  be  too 
rapid  for  the  best  results.  In  order  to  hasten  the  hardening  of 
mortar  and  plastering  in  new  houses,  builders  sometimes  build  coke 
or  charcoal  fires  in  open  grates  or  baskets.  But  this  is  liable  to 
cause  uneven  drying  and  excessive  shrinkage,  resulting  in  cracks  or 
scaled  places.  In  certain  mortars  hair  or  other  fibrous  material  is 
added  to  increase  the  toughness,  especially  while  wet. 

Since  mortar  does  not  harden  until  dry,  it  should  never  be  used 
in  damp  places,  such,  as  foundations  and  cellars,  nor  in  very  thick 
walls.  Sometimes  it  is  mixed  with  some  cement,  increasing  its 
strength  and  usefulness.  When  thoroughly  hardened,  good  mortar 
is  about  as  hard  as  limestone,  and  adheres  firmly  to  the  bricks  or 
stones  of  the  wall. 

CEMENT 

Cement  consists  of  certain  anhydrous  double  silicates  of  calcium 
and  aluminum,  which  are  capable  of  combining  chemically  with 
water,  to  form  a  hard  mass.  It  differs  from  lime  mortar  in  that  it 
hardens  while  wet,  does  not  require  the  presence  of  carbon  dioxide 
for  hardening,  and  is  very  insoluble  in  water.  It  is  very  well  adapted 
for  use  in  moist  places,  or  even  under  water,  and  since  its  hardening 
is  simultaneous  throughout  the  whole  mass,  and  is  quite  rapid  in 
most  varieties,  it  finds  extensive  use  in  building  operations. 

There  are  three  general  classes  of  cement :  — 

1.  Those  formed  from  certain  volcanic  tufas,  or  from  artificial 
mixtures  resembling  these.  Such  cements  generally  need  the  addi- 


LIME,   CEMENT,   AND  PLASTER  OF  PARIS  153 

tion  of  lime  before  they  display  hydraulic  properties,  i.e.  form 
insoluble  silicates  when  treated  with  water.  In  this  group  are  the 
natural  volcanic  tufas,  Pozzuolan,  trass,  and  Santorin  earth,  together 
with  blast  furnace  slags  and  certain  coal  ashes,  which  are  occasion- 
ally used. 

2.  Those  which  contain  a  large  proportion  of  free  lime,  having 
been  made  by  burning  natural  argillaceous  limestones  at  a  tempera- 
ture sufficiently  high  to  drive  off  all  the  carbon  dioxide,  but  not  to 
fuse  the  product.     These  include  "hydraulic  limes'7  (p.  150)  and 
Roman  cements. 

3.  Those  prepared  by  burning  an  intimate  mixture  of  clay  and 
powdered  calcium  carbonate,  at  a  very  high  temperature,  so  that 
incipient  fusion  takes  place  in  the  mass.     These  constitute  the  Port- 
land cements.  9 

Pozzuolanic  cements  are  chiefly  derived  from  volcanic  tufas, 
which  are  found  in  Italy,  near  Naples  (Pozzuoli),  in  the  islands 
of  the  Grecian  archipelago,  and  in  Germany  near  Andernach  on 
the  Rhine.  These  tufas  consist  of  silicates  which  are  easily  decom- 
posed by  acids.  They  have  resulted  from  the  action  of  volcanic 
fires,  and  need  no  further  treatment  than  fine  grinding  and  mix- 
ing with  lime.  Such  cements  are  slow  in  hardening,  but  have 
considerable  ultimate  strength.  Pozzuolan  has  been  used  since 
the  time  of  the  Romans,  who  were  well  acquainted  with  its  prop- 
erties. 

Blast  furnace  slag  is  now  used  to  some  extent  for  the  production 
of  cement.  But  in  order  to  develop  the  hydraulic  property,  the 
melted  slag  must  be  cooled  suddenly ;  this  is  usually  done  by  run- 
ning it  into  water.  The  granulated  material  thus  produced  is  then 
very  finely  ground  and  mixed  with  lime.  Some  slags  contain  a 
high  percentage  of  lime-alumina  silicate,  and  hence  need  less  addi- 
tion of  lime.  Slag  cements  have  not  given  entire  satisfaction  up 
to  the  present,  although  they  have  been  greatly  improved  within  a 
year  or  two,  by  increased  care  in  running  the  furnace  charges. 
These  cements  are  said  to  harden  more  slowly,  and  to  have  less 
resistance  to  the  action  of  frost  than  the  Portland  cements.  They 
shrink  considerably,  and  are  liable  to  crack,  but  this  is  remedied 
somewhat  by  coarse  grinding.  Slag  cements,  low  in  silica,  but  hav- 
ing a  high  percentage  of  iron,  do  not  harden  well. 

Hydraulic  limes  have  already  been  mentioned  (p.  150).  The  free 
lime  which  they  contain  is  sometimes  slaked  with  just  sufficient 
water  to  hydrate  the  quicklime  before  the  material  is  sold ;  but  not 
enough  water  should  be  added  to  set  the  cement. 


154  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

Roman  cement  is  made  by  burning  argillaceous  limestone  in  kilns. 
It  was  first  made  in  England  by  J.  Parker,  who  patented  a  process 
for  preparing  it  from  the  septaria  nodules,  consisting  of  clay  and 
chalk  found  in  the  bed  and  along  the  banks  of  the  Thames  River. 
Later,  the  beds  of  clay  limestones  were  used,  but  as  there  was  much 
irregularity  in  the  composition  of  these  rocks,  the  product  did  not 
give  satisfaction.  But  by  careful  selection  of  the  material  and 
proper  mixing  of  different  kinds  of  stone,  the  quality  of  cement  pro- 
duced has  been  improved.  These  rocks  are  also  found  in  France, 
Holland,  and  Germany,  and  in  the  United  States.  There  are  sev- 
eral deposits  that  are  very  pure,  and  vary  but  little  in  the  different 
parts  of  the  bed.  Roman  cement  was  first  made  in  this  country  in 
New  York  state,  from  a  rock  found  on  the  banks  of  Rondout  Creek 
and  near  the  Hudson  River,  and  is  called  "  Rosendale,"  from  the 
chief  town  in  the  district;  it  still  constitutes  a  large  part  of  the 
natural  cement  made  in  this  country.  Another  important  region  is 
on  the  Ohio  River,  near  Louisville,  the  cements  made  there  being 
known  by  the  latter  name.  Pennsylvania,  Illinois,  Wisconsin,  and 
Colorado  also  supply  much  natural  cement. 

Nearly  all  these  rocks  contain  a  large  percentage  of  mag- 
nesia, but  this  does  not  appear  to  injure  the  cement  made  from 
them. 

The  rock  is  broken  into  lumps  about  the  size  of  a  goose  egg,  in 
order  to  secure  evenness  in  burning.  The  burning  is  done  in  con- 
tinuous kilns,  as  a  rule,  and  the  temperature  must  be  very  carefully 
regulated,  high  enough  to  drive  out  nearly  all  of  the  carbon  dioxide, 
but  not  to  fuse  the  rock.  Then  the  rock  is  carefully  ground  between 
buhrstones,  and  sifted.  The  finer  the  grinding,  the  better  the 
product.  In  order  to  secure  supposed  uniformity  in  the  product,. it 
is  often  customary  to  mix  rock  from  several  beds,  in  the  same  kiln, 
but  this  is  of  doubtful  benefit. 

The  color  of  Roman  cement  varies  greatly,  from  pale  yellow  to 
red  brown,  and  is  due  chiefly  to  the  amount  of  iron  and  manganese 
oxides  present.  But  there  should  not  be  great  variations  in  the 
color  of  the  products  made  from  the  same  rock,  as  this  indicates 
inequality  in  burning. 

Roman  cement  is  generally  quick  setting,  and  hence  is  preferred 
by  many  engineers  for  work  under  water.  It  weighs  from  50  to 
56  pounds  per  cubic  foot.  Its  strength  is  inferior  to  Portland 
cement. 


LIME,   CEMENT,   AND   PLASTER   OF   PARIS 

The  following  analyses  *  are  of  typical  cement  rocks :  — 


155 


N.  Y.,  ULSTER 
COUNTY, 
ROSENDALE. 

ILLINOIS, 
UTICA. 

WISCONSIN, 
MILWAUKEE. 

PENNSYLVANIA, 
COPLAT. 

CaCO3              .... 

45.91 

42.25 

45.54 

67.14      *1 

M>CO3                 .     .     . 

26.14 

31.98 

32.46 

2.90     Y 

Si02       .                   .     . 

15.37 

21.12 

17.56 

18.34 

FesOi 

}Q  03 

A1203     
Na^O      

11.38 

1.12 

1.41 

7.49 
1 

K2O 

1   0.19 

H2O 

}1  07 

Undetermined      .     . 

1.20 

2.46 

~ 

3.94 

^ 


Analyses  of  natural  cements : 


KOSENDALE. 

UTICA. 

LOUISVILLE,  KY. 

LEHIGH  VALLEY. 

Si02  

22.75 

35.43 

21.10 

18.28 
}                j 

F  2Q 

16.70 

9.92 

7.51 

7.43      It 

CaO  

36.70 
16.65 

33.67 
20.98 

44.40 
7.00 

51.53 
2.07 

K2O                            .     . 

Na20 

— 

— 

0.80 

1.50 

C02   

5.00 

11.18 

16  20 

CaS04              .... 

6.85 

H2O                           .     . 

1  30 

1.16 

Undetermined     .     . 

— 

2QO 
.«7O 

Portland  cement  is  entirely  an  artificial  product,  but  represents 
the  most  important  branch  of  the  cement  industry.  The  first  patent 
was  taken  out  in  England,  in  1824,  but  the  process  extended  in  a 
few  years  to  France  and  Germany.  In  the  United  States  the  man- 
ufacture of  this  cement  was  begun  in  1878,  at  Coplay,  Penn.,  but  the 
industry  has  not  yet  developed  sufficiently  to  supply  more  than  one 
quarter  of  the  annual  consumption  in  this  country. 

The  materials  used  are  very  pure  calcium  carbonate  and  fine  clay, 
rich  in  silica.  The  English  manufacturers  prefer  chalk  and  clay 
mud  taken  from  the  mouth  (estuary)  of  the  Medway  River.  In  Ger- 

*  W.  A.  Smith,  Mineral  Industry,  Vol.  I,  1892. 


156 


OUTLINES  OF   INDUSTRIAL   CHEMISTRY 


many,  a  marl  (calcareous  clay)  is  employed.  But  in  any  case  the 
proportion  of  calcium  carbonate  to  clay  must  be  controlled  within 
tolerably  narrow  limits.  A  most  thorough  mixing  of  the  ingredi- 
ents is  very  essential.  The  calcium  carbonate  and  clay  are  both 
finely  ground,  and  often  levigated,  before  they  are  mixed.  There 
are  two  methods  of  mixing  in  general  use :  the  semi-dry  and  the 
wet.  In  the  semi-dry  method,  the  materials  are  mixed  in  a  wash- 
mill  to  a  thick  "  slurry,"  containing  about  40  per  cent  of  water,  and 
which  is  then  ground  again  in  buhrstone  mills ;  then  it  is  run  into 
shallow  pits,  where  much  of  the  water  drains  away  or  evaporates. 
Sometimes  it  is  dried  by  the  waste  heat  from  the  kilns.  When  dry 
enough  to  work  properly,  the  mass  is  made  into  balls  or  bricks 
(usually  by  machines)  and  dried,  after  which  they  are  ready  for  burn- 
ing. In  the  wet  method,  the  clay  and  chalk  are  ground  together, 
and  the  slurry  levigated,  so  that  all  coarse  particles  are  eliminated. 
After  settling,  the  water  is  drawn  off,  and  the  slime  dried  by  waste 
heat  and  bricked,  as  in  the  semi-dry  method.  The  dry  bricks  are 
then  burned. 

Several  varieties  of  kilns  are  in  use  for  burning  Portland  cement. 
Periodic,  dome-shaped,  or  shaft  kilns  are  still  much  used  in  this  coun- 
try, but  are  uneconomical  as  to  fuel  and  output.  Coke  is  used  as 

fuel,  and  is  charged  into  the  kiln  in  alter- 
nate layers  with  the  bricks.  The  coke, 
amounting  to  40  per  cent  of  the  weight 
of  the  clinker,  is  burned  out,  and  the  kiln 
cools  and  is  emptied. 

Continuous  kilns  are  coming  into 
more  general  use,  however.  The  great 
difficulty  at  first  encountered  with  them 
was  the  tendency  of  the  charge  to  stick 
to  the  furnace  walls,  owing  to  the  high 
temperature.  But  this  is  largely  avoided 
now  by  proper  attention  to  the  kiln  while 
burning. 

The  Dietsch  two-storied  kiln  (etageoferi) 
(Fig.  58)  is  much  used  for  Portland  ce- 
ment.    The  bricks  and  fuel  (which  may 
be  soft  coal)  are  charged  continuously  at 
the  top  (A),  and  descend  into  the  horizon- 
tal chamber  (B),  from  which  the  charge  is  raked  into  the  combus- 
tion chamber  (C)  by  introducing  a  tool  through  the  door  (D).     The 
burned  clinker  is  withdrawn  at  the  bottom  opening  (E).     Air  enters 


LIME,   CEMENT,    AND   PLASTER   OF   PARIS 


157 


at  (E),  and  passing  through,  the  hot  clinker,  arrives  in  (C)  at  a  very 
high  temperature,  where  it  supports  the  combustion  of  the  fuel. 
The  hot  gases  passing  off  through  (B)  and  (A)  serve  to  heat  the 
charge  before  it  arrives  in  (C).  These  kilns  now  are  often  worked 
with  forced  draught,  and  produce  about  7  tons  of  clinker  per  ton 
of  coal. 

Hoffmann's  ring  furnace  (Fig.  59)  is  also  much  used  in  cement 
burning.  This  consists  of  an  elliptical  gallery  built  around  a  cen- 
tral chimney  (A).  The  gallery  is  divided  into  15  or  20  compart- 
ments (B,  B),  each  having  a  door  (C)  opening  outside,  a  flue  (D) 
leading  to  the  chimney  (A),  and  a  wide  opening  (E)  into  the  next 
compartment.  Each  flue  has  a  damper,  by  which  connection  with 
the  chimney  (A)  may  be  opened  or  closed.  The  openings  (E) 
between  the  compartments  may  be  closed  with  a  sheet-iron  or  heavy 
paper  diaphragm,  as 
will  be  explained  be- 
low. If  the  door  of 
the  compartment  on 
one  side  of  the  dia- 
phragm be  opened, 
and  the  damper  of 
the  flue  (D)  leading 
from  the  compart- 
ment on  the  other 

side  of  the  diaphragm  is  also  opened,  while  all  the  other  doors 
and  flues  are  closed,  the  draught  of  the  chimney  (A)  will  cause  air 
to  enter  the  open  door  and  pass  around  the  entire  gallery,  through 
each  compartment  in  succession,  and  finally  out  through  the  open 
flue  (D)  to  the  chimney.  In  the  roof  over  the  gallery  are  charg- 
ing holes  (G),  several  being  in  each  compartment,  through  which 
fuel  is  introduced.  The  furnace  is  run  as  follows:  Assume  that 
there  are  14  compartments,  as  shown.  Twelve  compartments  con- 
tain cement  bricks,  and  their  doors  and  chimney  flues  are  closed. 
Suppose  that  No.  1  is  being  emptied,  while  No.  14  is  being  filled. 
The  paper  diaphragm  closes  the  opening  between  No.  13  and  No. 
14,  and  the  flue  (D)  of  No.  13  is  open  to  the  chimney.  Compart- 
ment No.  7  is  at  the  height  of  combustion,  while  Nos.  G,  5,  4,  3,  2 
contain  bricks  which  have  been  burned.  In  Nos.  8,  9,  10,  11,  12  are 
bricks  to  be  burned.  Cold  air  is  drawn  in  through  the  open  door 
of  No.  1,  and  passing  in  order  through  Nos.  2,  3,  4,  5,  6  becomes 
heated  by  contact  with  the  hot  bricks  in  these  compartments  until, 
after  passing  through  No.  6,  which  is  still  red  hot,  it  arrives  in  No. 


FIG.  59. 


158  OUTLINES  OF  INDUSTRIAL   CHEMISTRY 

7  at  a  very  high  temperature.  In  No.  7  the  fuel  is  burning  at  a 
white  heat,  and  the  hot  gases  pass  on  through  Nos.  8,  9,  10,  11,  12, 
13,  from  which  they  escape  to  the  chimney.  By  this  passage  of 
the  hot  gases  through  the  compartments,  the  unburned  bricks  are 
heated,  those  in  No.  8  being  nearly  red  hot ;  but  as  no  fuel  has  been 
introduced  into  these  chambers,  combustion  and  white  heat  are  con- 
fined to  No.  7.  When  No.  14  is  filled  with  green  bricks,  its  doors 
are  closed,  and  also  the  chimney  damper  of  No.  13,  while  that  of 
No.  14  is  opened,  and  the  diaphragm  transferred  to  the  opening 
between  No.  14  and  No.  1.  Fuel  is  now  introduced  into  No.  8, 
which  becomes  the  combustion  chamber,  and  the  door  of  No.  2  is 
opened.  The  burned  bricks  in  No.  2,  having  been  cooled  by  the 
passage  of  cold  air,  are  taken  out,  while  No.  1  is  being  refilled. 
Thus  the  cycle  of  operations  goes  on,  each  compartment  in  turn 
being  charged  with  fuel  and  made  the  combustion  chamber.  The 
temperature  in  that  compartment  which  has  just  been  filled  is  only 
high  enough  to  dry  the  green  bricks  well.  A  paper  diaphragm  is 
often  used  between  this  chamber  and  the  next  one,  which  is  to  be 
filled.  When  the  temperature  becomes  sufficiently  high  to  burn 
away  this  paper,  the  next  compartment  is  ready,  and  is  thrown 
into  the  circuit. 

This  furnace  is  very  economical  of  fuel,  one  ton  of  soft  coal 
burning  6|-  tons  of  clinker,  but  it  requires  much  labor.  The  bricks 
must  be  accurately  piled  in  order  that  open  channels  may  be  left 
beneath  the  charging  holes  for  the  fuel,  which  is  thus  made  to  burn 
in  a  column  extending  from  the  floor  to  the  top  of  the  furnace. 
The  fuel  must  not  contain  too  much  ash.  Usually  one  compartment 
is  emptied  each  day,  and  consequently  the  fire  is  moved  forward 
each  day. 

Revolving  furnaces  (p.  17)  are  also  used  to  some  extent  for 
cement  burning.  A  furnace  used  in  this  country  is  about  75  feet 
long,  slightly  inclined,  and  lined  with  fire-brick.  The  lower  end  is 
6  feet  in  diameter  and  the  upper  end  5  feet.  Crude  petroleum  is 
used  as  fuel,  and  the  furnace  is  continuous  acting.  The  wet 
slurry  runs  in  at  the  upper  end  and,  by  drying  on  the  rotating 
surface,  forms  little  balls  or  gravel-like  lumps  which  are  thoroughly 
burned  in  the  passage  through  the  furnace,  requiring  two  hours  or 
more.  The  annual  increase  in  output  from  rotary  furnaces  indicates 
that  the  method  is  a  successful  one.  Producer  gas  will  probably 
soon  take  the  place  of  crude  petroleum,  should  the  price  of  the 
latter  advance  much. 

Much  depends  on  the  proper  temperature  of  the  burning,  during 


LIME,   CEMENT,   AND   PLASTER  OF  PARIS  159 

which  there  is  considerable  shrinkage ;  well  burned  clinker  is  a 
semi-vitrified,  brown  or  grayish  green  mass.  If  overburned,  it  may 
fuse  and  take  on  a  blue  green  or  black  color  j  such  cement  will  not 
combine  with  water. 

The  clinker  is  then  ground  very  fine,  so  that  nearly  the  whole  of 
it  will  pass  through  a  sieve  with  2500  meshes  to  the  square  inch. 
Buhrstone  or  ball-mills  are  generally  used  for  this  purpose.  The 
Griffin  mill,  which  consists  of  a  heavy  steel  roll  revolving  about  a 
vertical  shaft,  and  pressing,  by  centrifugal  force,  against  a  steel 
ring,  is  proving  very  effective.  Since  only  the  finest  dust  is  of 
value  in  cement,  great  care  is  necessary  to  prevent  the  coarse 
material  from  passing  through  the  mill.  After  grinding  it  is  gen- 
erally stored,  that  any  free  lime  it  contains  may  become  air-slaked, 
before  the  cement  goes  to  market. 

The  composition  of  Portland  cements  varies  somewhat,  but  the 
following  are  the  extremes  :  — 

Silica 19.80  ....  26.45 

Alumina 4.16  ....  9.45 

Ferric  oxide 2.19  ....  4.47 

Lime 58.22  ....  65.59 

Magnesia traces  ....  2.89 

Alkalies    ........  0.19  ....  2.83 

Sulphuric  acid 0.19  ....  2.19 

Loss  on  ignition 0.26  ....  2.67 

Undetermined  residue     ...  0.12  ....  1.28 

The  cause  of  hardening  of  cements  has  been  investigated  by 
many  chemists  and  has  caused  much  discussion.  Le  Chatelier's  * 
investigations  show  that  during  the  burning  a  tricalcium  silicate 
(Ca3Si05)  is  formed  by  the  action  of  the  clay  on  the  lime.  At  the 
same  time  a  certain  amount  of  calcium  aluminate  and  ferrite  are 
also  formed,  besides  mono-  and  di-calcium  silicates.  When  treated 
with  water  the  tricalcium  silicate  reacts  to  form  a  hydrated  mono- 
calcium  silicate  and  calcium  hydroxide :  — 

1)  2  C%Si05  +  9  H20  =  (CaSi03)2  •  5  H20  +  4  Ca  (OH)* 

Then  a  reaction  between  the  calcium  hydroxide,  water,  and  calcium 
aluminate  may  occur,  forming  a  hydrated  basic  calcium  aluminate:  — 

2)  Ca3Al  A  +  Ca(OH)2  + 11  H20  =  Ca4Al207  •  12  H20. 

The  formation  of  the  hydrated  basic  aluminate  (CaO)4,  A1203  •  12  H20, 
probably  exerts  some  influence  on  the  rapidity  of  the  "  setting  "  of 

*  Annales  des  Mines,  1887,  388.  J.  Soc.  Chem.  Ind.,  1888,  567,  847.  Thonin- 
dustrie  Zeitung,  1892  (16)  1032.  Chemiker  Zeitung,  1892,  Ref.  342. 


160  OUTLINES  OF   INDUSTRIAL   CHEMISTRY 

the  cement,  but  the  hardening  is  undoubtedly  due  to  the  first  re- 
action. The  "  set "  of  cement,  in  contrast  with  that  of  mortar,  is 
not  due  to  a  drying  out  of  water,  but  is  the  beginning  of  the  true 
hardening  process.  The  rapidity  of  this  "  setting  "  is  influenced  by 
the  presence  of  other  salts ;  alkalies  hasten  it,  while  it  is  retarded 
by  calcium  sulphate,  magnesium  sulphate  and  chloride,  and  sodium 
chloride.  It  is  also  retarded  proportionally  as  the  amount  of  sand 
used  is  increased.  The  amount  of  water  used  in  mixing  is  about 
one-third  the  weight  of  the  cement,  and  its  temperature  has  much 
to  do  with  the  rate  of  "  setting,"  warm  water  hastening  it. 

Portland  cement  is  usually  slower  in  setting  than  Roman,  but 
when  the  hardening  has  begun  it  progresses  more  rapidly  with  the 
former.  There  is  very  little  increase  of  hardness  after  six  months. 
Portland  cement  is  more  durable  than  Roman  under  most  conditions, 
and  is  generally  stronger.  It  forms  a  denser  and  heavier  powder  of 
a  greenish  gray  color,  but  when  hardened  has  a  drab  shade  resem- 
bling the  color  of  the  stone  quarried  at  Portland,  England,  and  used 
much  for  building  in  that  country ;  hence  the  name.  As  has  been 
said,  variations  in  color  of  the  same  brand  of  cement  may  show 
changes  in  quality ;  if  underburned,  it  is  generally  yellowish.  The 
weight  per  cubic  foot  varies  from  about  70  to  90  pounds ;  the  finer 
the  grinding,  the  less  the  weight.  But  as  a  rule  heavy  cements  are 
preferred  by  builders,  as  they  are  supposed  to  be  more  thoroughly 
burned ;  they  are,  however,  slow  in  setting. 

The  testing  of  cement  is  generally  the  work  of  the  engineer, 
rather  than  the  chemist.  Chemical  analysis  is  of  but  little  use  in 
determining  its  properties,  and  the  usual  tests  applied  are  phy- 
sical. They  are  for :  — 

(a)  Fineness. 

(6)   Expansion  ("Blowing"). 

(c)    Shrinkage. 

(cf)  Rate  of  hardening. 

(e)   Resistance, 

to  tension 

to  compression. 

A  committee  of  the  American  Society  of  Civil  Engineers  has 
recommended  certain  standard  requirements  for  cements.*  In  Ger- 
many, an  official  standard  and  method  of  testing  have  been  adopted. 

In  testing  the  fineness,  three  sieves  should  be  used,  —  Nos.  50, 
74,  and  100,  the  proportion  of  each  sample  rejected  by  each  sieve  to 
*  Transactions  American  Society  of  Civil  Engineers,  November,  1885. 


LIME,   CEMENT,   AND   PLASTER  OF   PARIS  161 

be  determined  by  weighing.  The  residue  remaining  in  the  coarse 
sieves  is  of  little  more  value  than  the  same  quantity  of  sand. 

Expansion,  or  "  blowing,"  is  shown  by  the  swelling  and  cracking 
of  a  pat  of  cement,  three  inches  in  diameter,  one-half  inch  thick  in 
the  middle,  and  very  thin  at  the  edges.  After  setting,  a  pat  of  this 
kind  is  put  into  water  and  left  several  weeks,  being  examined  every 
day.  If  fine  cracks  appear  in  the  edges,  or  disintegration  occurs, 
the  cement  is  of  poor  quality.  Expansion  may  be  caused  by  the 
presence  of  unslaked  lime,  magnesia,  or  gypsum,  or  the  cement  may 
be  underburned.  Expansion  and  shrinkage  tests  are  often  made  by 
filling  glass  bottles  or  lamp  chimneys  with  the  freshly  mixed 
cement.  After  setting,  any  expansion  will  crack  the  glass.  Colored 
water  may  be  poured  on  top  of  the  cement.  If  it  runs  down  be- 
tween the  cement  and  the  glass,  shrinkage  has  probably  taken  place. 

The  rate  of  hardening,  or  the  time  of  setting,  is  very  important 
in  determining  the  suitability  of  a  cement  for  a  given  purpose. 
Quick-setting  cements  are  usually  desirable  for  work  under  water. 
The  time  is  determined  by  the  "  normal  needle/'7  *  Two  of  these 
are  used.  One  is  a  wire  about  one-twelfth  of  an  inch  in  diameter, 
and  is  loaded  with  a  weight  of  one  quarter  of  a  pound.  The  other 
is  one  twenty-fourth  of  an  inch  in  diameter,  and  carries  a  weight 
of  one  pound.  After  mixing  the  cement  with  water,  the  time  is 
noted  until  no  impression  is  made  upon  it  by  the  point  of  the  first 
wire.  This  is  the  beginning  of  the  "  setting."  When  the  second 
wire  will  no  longer  penetrate,  the  "  set "  is  ended.  Cement  which 
will  set  in  less  than  two  hours  is  called  "quick  setting";  those 
taking  a  longer  time  are  "  slow  setting."  The  beginning  of  the  set 
is  sometimes  noticed  within  five  or  ten  minutes  after  mixing,  and 
usually  within  half  an  hour.  It  is  important  that  the  work  be  not 
disturbed  after  the  "  set "  is  once  established,  otherwise,  tight  and 
strong  joints  cannot  be  made. 

The  resistance  tests  are  the  most  important.  In  actual  use, 
cements  are  generally  subjected  to  compression  strains;  but  since 
compression  tests  are  difficult  to  make,  it  is  often  the  practice  to 
make  only  the  tension  tests.  Both  tests  should  be  made  if  possi- 
ble from  samples  taken  from  the  barrel,  and  from  the  sifted  cement 
which  passes  the  No.  100  sieve,  as  well  as  with  these  samples  when 
mixed  with  various  weights  of  standard  sand.  This  sand  is  made 
by  pulverizing  quartz ;  it  is  sifted  and  the  portion  used  which  passes 
a  No.  20  sieve,  and  is  retained  by  a  No.  30. 

*  Transactions  American  Society  of  Civil  Engineers,  1893  ;  The  Testing  of  Port- 
land Cement,  by  Max  Gary. 


162  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

For  tension  tests,  the  cement  is  mixed  with  water  and  filled  into 
a  metal  mould,  forming  a  "  briquette,"  shaped  like  an  hour-glass,  the 
narrow  portion  having  a  section  exactly  one  inch  square.  The 
briquettes  must  be  made  very  carefully,  or  the  results  will  not  be 
uniform.  The  cement  is  quickly  mixed  with  water  at  60°  F.,  filled 
into  the  mould,  pressed  down  well  and  smoothed  off  evenly.  This 
is  done  on  a  slate  or  glass  plate,  to  prevent  absorption  of  moisture. 
As  soon  as  set,  the  briquette  is  removed  and  allowed  to  stand 
covered  with  a  wet  cloth  for  24  hours.  It  is  then  placed  in  water, 
where  it  remains  until  the  test  is  made,  when  it  is  fixed  in  the  jaws 
of  a  machine,  which  applies  a  gradually  increasing  tension.  The 
number  of  pounds  necessary  to  fracture  the  briquette  is  read  on  a 
graduated  scale  beam.  The  average  of  five  or  ten  tests  is  taken  as 
the  breaking  strength. 

The  briquettes  are  usually  tested  at  one  day,  one  week,  and  four 
weeks  after  making.  Sometimes  they  are  kept  for  still  longer 
periods.  When  made  from  cement  without  sand,  they  are  called 
"  neat."  The  proportions  of  sand,  water,  and  cement  recommended 
are:  — 

For  Portland  briquettes  (neat),  25  per  cent  of  water. 

For  natural  cement  (Rosendale)  (neat),  30  per  cent  water. 

For  1  part  cement,  and  1  part  sand ;  the  water  used  is  about 
15  per  cent  of  the  total  weight  of  the  sand  and  cement. 

Another  proportion  is :  cement,  1  part ;  sand,  3  parts ;  and  water 
to  about  12  per  cent  of  the  total  weight  of  sand  and  cement. 

Compression  tests  are  made  on  small  cubes  of  the  cement  in 
question.  They  should  show  at  least  ten  times  their  tension 
resistance.  But,  as  has  already  been  said,  this  test  is  difficult  to 
make,  and  is  very  frequently  omitted. 

Chemical  analysis  of  cement  is  seldom  employed,  and  chiefly 
to  detect  the  presence  of  adulterants.  Formerly,  the  most  common 
adulterant  was  ground  blast  furnace  slag;  but  clay,  ashes,  and 
hydraulic  lime  have  been  employed,  and  are  not  always  easy  to 
detect.  The  specific  gravity  of  good  Portland  cement  should  not  be 
less  than  3.1,  but  adulterants  may  reduce  it.  The  presence  of  con- 
siderable quantities  of  manganese  would  also  indicate  adulteration. 

Magnesia  in  Portland  cement  is  claimed  to  cause  expansion,  and 
3  per  cent  is  the  highest  allowable.  In  Roman  cement,  however, 
a  large  amount  is  sometimes  present  without  apparent  injury. 
Alkalies  in  considerable  quantities  are  also  questionable  ingredi- 
ents ;  not  more  than  2.5  per  cent  should  be  present  in  a  good 
Portland  cement. 


LIME,   CEMENT,   AND   PLASTER  OF  PARIS  163 


PLASTER    OF   PARIS 

Plaster  of  Paris  is  made  by  heating  the  mineral  gypsum 
(CaS04  •  2  H20)  until  about  three-fourths  of  its  water  of  crystal- 
lization has  been  driven  off.  The  process  is  called  burning,  and 
is  usually  carried  on  in  kilns,  muffle  furnaces,  or  retorts.  Direct 
contact  with  the  fuel  is  not  permitted,  lest  the  action  of  the  car- 
bonaceous matter  should  cause  a  reduction  of  some  of  the  calcium 
sulphate  to  sulphide.  Neither  should  the  flame  come  in  contact 
with  the  gypsum,  but  only  the  hot  gases.  The  burning  is  a  very 
delicate  operation,  and  requires  much  care. 

Gypsum  contains  about  21  per  cent  of  water  of  crystallization, 
of  which  good  plaster  should  retain  4  or  5  per  cent.  The  loss  of 
water  begins  at  about  80°  C.,  but  the  most  favorable  temperature 
for  burning  is  about  125°  C.  If  heated  to  200°  C.,  all  the  crystal 
water  is  expelled,  and  the  product  will  combine  with  water  but  very 
slowly,  the  property  of  rapid  setting  having  been  destroyed.  Thus 
it  will  be  seen  that  the  limits  of  heating  are  very  narrow. 

The  gypsum  is  broken  in  rather  small  lumps  to  secure  evenness 
in  burning;  for  a  fine  product,  it  is  sometimes  powdered  and 
heated  on  a  plate,  while  constantly  stirred.  After  burning,  the 
lumps  are  friable  and  are  easily  ground.  Sometimes  wooden  rolls, 
set  edge-runner  fashion,  are  used  to  grind  the  burned  material. 

When  mixed  with  water,  plaster  of  Paris  forms  a  paste  which 
soon  hardens  or  "  sets,"  owing  to  a  recombination  of  water  with  the 
burned  plaster,  to  form  hydrated  calcium  sulphate.  The  theory  of 
this  setting  has  been  explained  by  Le  Chatelier.*  The  composition 
of  the  plaster  is  essentially  (CaS04)2  •  H^O*  a  salt  which  is  soluble, 
and  part  of  which  dissolves  in  the  water  used  in  mixing.  But  as 
soon  as  it  dissolves,  a  combination  between  it  and  some  of  the  water 
takes  place,  forming  CaS04  •  2  H20 ;  this,  being  much  less  soluble 
than  the  monohydrated  salt,  at  once  begins  to  crystallize  from  the 
solution,  forming  a  network  of  crystals.  Then  more  of  the  plaster 
dissolves,  becomes  fully  hydrated,  and  crystallizes  out,  increasing 
the  solidity  of  the  "set"  by  the  interlacing  of  new  crystals  with 
those  already  formed.  Thus  the  cycle  of  reactions  goes  on  until 
the  plaster  is  fully  hydrated. 

The  theoretical  quantity  of  water  necessary  to  set  plaster  is 
about  18  per  cent  of  its  weight ;  but  in  fact,  from  30  to  35  per  cent 
is  generally  used.  Excess  of  water  renders  the  mass  more  plastic 

*Comptes  Rendus,  Vol.  96,  717,  1668. 


164  OUTLINES   OF  INDUSTRIAL   CHEMISTRY 

and  retards  the  setting.  Very  great  excess  may  cause  disintegration 
of  the  plaster,  if  left  in  contact  with  it  for  some  time  after  setting, 
owing  to  the  solution  of  some  of  the  crystallized  calcium  sulphate. 

Plaster  expands  slightly  while  setting,  and  for  this  reason  is 
valuable  for  making  casts  and  reproductions.  It  is  largely  used  for 
interior  decorative  work  and  also  as  a  cement  for  joining  glass  and 
metal  ware.  The  surface  of  plaster  after  setting  is  rather  soft,  and 
for  many  purposes  it  is  desirable  to  increase  the  hardness.  This 
may  be  done  by  mixing  alum,  borax,  or  tartaric  acid  with  it,  or  by 
adding  some  alcohol  to  the  water  with  which  the  plaster  is  mixed. 
However,  these  substances  retard  the  setting.  By  painting  or  dip- 
ping plaster  casts  in  melted  wax,  paraffine,  or  stearin,  or  in  solu- 
tions of  these  in  petroleum  ether,  the  pores  of  the  plaster  mass  are 
filled  and  the  surface  is  made  smooth,  so  that  dirt  will  not  adhere 
and  the  articles  may  be  washed.  When  treated  with  a  solution  of 
barium  hydroxide,  the  surface  of  the  plaster  is  coated  with  barium 
sulphate  and  rendered  insoluble.  If  plaster  is  mixed  with  a  solu- 
tion of  glue  or  size,  the  material  called  "  stucco  "  is  obtained. 

REFERENCES 

Die  hydraulische  Morter.     Michaelis,  1869. 

A  Practical  Treatise  on  Limes,  Hydraulic  Cement,  and  Mortars.    Q.  A.  Gilmore, 

1874. 
Transactions  of  the  American  Society  of  Civil  Engineers  :  — 

1877  (Dec.).     W.  F.  Maclay. 

1885  (Nov.)-     Report  of  Committee  on  Cement  Tests. 

1885  (Apr.).     E.  C.  Clarke. 

1893.  Max  Gary. 

Chemisohe  Technologic  der  Mortelmaterialien.    G.  Feichtinger,  1885. 
Journal  of  the  Society  of  Chemical  Industry  :  — 

1886,  188,  199.     W.  C.  Unwin. 

1891,  927. 
Recherches  expe"rimentales  sur  la  Constitution  des  Mortiers  hydrauliques.     Le 

Chatelier,  Paris,  1887. 
Annales  des  Mines  :  — 

XI  (1887),  388-465.     H.  Le  Chatelier. 
Fabrication  et  Controlle  des  Chaux  hydrauliques  et  des  Ciments.     H.  Bonnami, 

Paris,  1888.     (Gauthier-Villars  et  Fils.) 

Zsment  und  Kalk.     Rudolf  Tormin,  Weimar,  1892.     (B.  F.  Voigt.) 
A  Manual  of  Lirne  and  Cement.     A.  H.  Heath,  London,  1893.     (E.  and  F.  N. 

Spon.) 
Journal  of  American  Chemical  Society  :  — 

1894,  161.     Thomas  B.  Stillman. 

For  a  more  complete  bibliography,  see  Thorpe's  Dictionary  of  Applied  Chemis- 
try, Vol.  I,  pp.  488,  489. 


GLASS 


GLASS 

Glass  is  an  amorphous,  transparent  or  translucent  mixture  of 
silicates,  one  of  which  is  always  that  of  an  alkali.  The  usual  silicates 
employed  are  those  of  potassium,  sodium,  calcium,  and  lead ;  the  sili- 
cates of  heavy  metals  occur  in  the  colored  glasses.  Glass  is  not 
readily  decomposed  by  water  or  acids  (excepting  HF).  Its  behavior 
towards  solvents  generally,  tends  to  show  that  it  is  a  mixture  of 
silicates,  rather  than  a  definite  compound. 

Most  simple  silicates  and  mixtures  of  them  are  difficult  to  fuse, 
and  when  cooled  after  fusion,  have  a  crystalline  structure ;  but  the 
alkali-lime  and  alkali-lead  silicates  fuse  easily,  and  are  generally 
amorphous  after  fusion.  Furthermore,  they  have  no  sharp  melting 
point,  and  consequently,  when  allowed  to  cool  after  fusion,  glass 
first  becomes  pasty  and  then  rigid.  This  property  of  plasticity 
while  hot  permits  its  use  for  many  articles  which  could  not  other- 
wise be  made  from  it;  glass-blowing  would  be  impossible,  and 
only  cut  or  cast  ware  could  be  made.  G-lass  is  amorphous  when 
cooled  rapidly  from  a  state  of  fusion,  but  if  cooled  very  slowly  and 
in  a  large  mass,  there  is  sometimes  a  tendency  of  the  component 
silicates  to  crystallize,  causing  the  glass  to  lose  its  transparent 
character,  and  become  white  or  porcelain-like  in  appearance.  The 
same  effect  is  produced  if  it  is  kept  near  its  melting  temperature  for 
a  long  time.  This  phenomenon,  known  as  devitrification,  is  due  to 
a  physical  change  only,  i.e.  crystallization. 

The  chemical  composition  of  glass  varies  considerably,  even  in 
the  same  kinds,  but  the  best  varieties  seem  to  approach  a  definite 
chemical  formula;  thus,  soda-lime  glass  approaches  Na20,  CaO, 
6  Si02,  and  lead  glass,  K20,  PbO,  6  Si02 :  but  it  may  vary  so  much 
that  the  formula  becomes  5  K2O,  7  PbO,  36  Si02.  Of  course  potash 
may  be  substituted  for  soda,  or  vice  versa,  in  either  kind,  while  the 
relative  proportion  of  the  several  ingredients  may  vary  between 
quite  wide  limits.  But  as  a  rule,  the  higher  the  percentage  of 
silica,  the  harder,  more  difficultly  fusible,  and  more  brittle  the  glass. 
Increase  of  alkali  makes  it  softer,  more  fusible,  and  less  capable  of 
resisting  atmospheric  changes  and  chemical  reagents.  Increasing 
the  percentage  of  lime  decreases  the  fusibility  and  renders  it  harder, 
but  not  so  brittle  as  in  the  case  of  high  silica  content.  If  the  alkali 
used  be  mixed  soda  and  potash,  a  more  fusible  glass  is  obtained 
than  from  either  alone.  Part  of  the  lime  or  lead  may  be  replaced 


166  OUTLINES  OF  INDUSTRIAL   CHEMISTRY 

by  oxides  of  other  metals,  e.g.  of  iron,  manganese,  cobalt,  copper, 
barium,  zinc,  tin,  arsenic,  etc.,  and  this  is  generally  the  case  to  some 
extent,  in  common  glass,  and  to  a  greater  degree  in  colored  glass. 
Aluminum  oxide  may  replace  some  of  the  silica ;  the  former  is  often 
present  in  considerable  amounts,  and  renders  the  product  tough. 
Certain  fluorides,  e.g.  calcium  fluoride,  also  enter  into  the  composition 
of  some  varieties.  Besides  the  above-named  oxides,  certain  borates 
and  phosphates  are  occasionally  used,  to  replace  a  part  of  the  silica 
in  glass  manufactured  for  various  optical  and  chemical  purposes; 
these  usually  contain  zinc  or  barium  also.  The  well-known  "  optical 
glass,"  made  in  Germany,  contains  both  zinc  and  boron. 

Technically,  two  kinds  of  glass  are  recognized:  lime  glass  and 
lead  glass.  The  alkali  used  may  be  soda,  or  potash,  or  both.  Lime 
glass  is  most  common  and  generally  useful.  It  is  cheaper,  harder, 
more  resistive,  and  less  fusible  than  lead  glass ;  the  latter  has  greater 
lustre  and  brilliancy,  is  heavy  and  expensive  and  is  used  chiefly  for 
cut  ware  and  for  optical  purposes. 

The  essential  materials  for  glass  making  are  silica,  an  alkali, 
and  lime  or  lead. 

Silica  was  formerly  derived  from  quartz  or  flint ;  but  this  is  now 
only  used  for  a  particularly  fine  quality.  It  is  heated  to  a  red  heat, 
and  dropped  into  water,  and  the  friable  mass  so  formed  is  powdered 
in  a  mill.  Quartz  sand  and  soft  quartzites  are  the  usual  sources 
of  silica,  and  numerous  deposits  are  worked  in  different  countries. 
Sand  of  great  purity  is  found  in  Germany,  near  Aix-la-Chapelle,  and 
at  Niviltein  ;  in  France,  at  Fontaine bleau ;  in  Belgium ;  in  England ; 
and  in  Australia.  In  the  United  States,  extensive  beds  are  worked 
in  Berkshire  Co.,  Mass.,  and  in  Pennsylvania,  along  the  Juniata 
Eiver.  The  Berkshire  deposit  is  a  soft  white  sandstone,  which, 
when  crushed,  yields  sand  which  is  from  99.6  to  99.8  pure  Si02. 
The  Juniata  stone  is  slightly  yellow  in  color,  a/id  the  sand  is  from 
98.8  to  99.7  pure  Si02.  The  most  troublesome  impurity  in  sand 
is  iron;  for  white  glass,  there  should  never  be  more  than  0.5  per 
cent  Fe203. 

Alkali  is  derived  from  the  carbonate  or  sulphate  of  soda  or 
potash,  and  these  also  must  be  free  from  iron.  Carbonate  fuses 
more  readily  with  the  sand  than  does  sulphate,  but  since  the  latter 
is  cheaper,  it  is  much  used.  It  is  essential  to  mix  carbon  in  some 
form  with  the  sulphate,  to  assist  in  reduction.  For  better  grades  of 
glass,  charcoal  dust  is  used,  but  for  common  glass,  powdered  coal  is 
the  reducing  agent.  The  exact  nature  of  the  reaction  with  sulphate 
appears  somewhat  uncertain :  — 


GLASS 

2  Na2S04  +  6  Si02  +  C  =  2  (Na20, 3  Si02)  +  2  S02  +  C02.* 
2  Na2S04  +  2  Si02  +  C  =  2  Na2Si03  +  2  S02  +  C02.t 

For  lead  glass,  sulphates  are  not  generally  used,  since  some 
sodium  sulphide  is  formed  by  the  reduction  of  the  sulphate,  and  this 
reacts  with  the  lead,  forming  lead  sulphide,  which  darkens  the  glass. 

Attempts  to  use  salt  directly  in  the  glass  furnace,  as  a  source  of 
alkali,  have  not  as  yet  proved  satisfactory.  It  is  quite  volatile  at 
the  temperature  of  the  furnace,  and  the  presence  of  air  or  steam  is 
necessary  for  its  decomposition  by  the  silica. 

For  potash,  crude  pearlash  is  much  used ;  but  in  the  better  grades 
of  glass  the  refined  pearlash  is  employed.  Sulphate  of  potassium  is 
difficult  to  reduce,  and  is  not  much  used. 

Lime  is  now  derived  from  chalk  or  limestone.  For  very  fine 
glass,  pure  marble  dust,  as  free  as  possible  from  iron,  is  employed. 
For  common  grades,  less  pure  limestone  is  used.  It  may  contain  a 
high  percentage  of  silica  and  considerable  alumina,  but  magnesia  or 
iron  in  large  amounts  is  objectionable.  Magnesia  makes  the  glass 
hard  and  infusible.  In  cheap  glass,  limestone  is  sometimes  replaced 
in  part  by  felspar,  porphyry,  or  granite.  Carbonates  of  both  alkali 
and  lime  are  advantageous  in  the  glass  mixture,  since,  as  the  mass 
fuses,  the  escaping  bubbles  of  carbon  dioxide  serve  to  stir  up  and 
mix  the  ingredients  more  thoroughly. 

Lead  is  added  as  litharge  (PbO),  or  red  lead  (Pb304).  The  latter 
is  preferred,  since  the  oxygen  liberated  from  it  is  thought  to  assist 
in  decolorizing  the  glass  by  oxidizing  the  iron;  it  also  prevents 
reduction  of  metallic  lead.  It  is  essential  that  the  litharge  and  red 
lead  be  free  from  copper. 

Besides  the  above  requisites,  it  is  customary  to  employ  other 
ingredients  in  every  glass  mixture,  to  assist  in  the  decolorization  or 
fusion.  The  commonest  decolorizing  material  added,  is  pyrolusite 
(binoxide  of  manganese,  Mn02).  Iron,  when  in  the  ferrous  condi- 
tion, imparts  a  deep  green  color  to  glass;  but  when  in  the  ferric 
state,  it  is  much  less  troublesome,  since  it  only  gives  a  pale  yellow 
color.  By  .the  oxidizing  action  of  the  pyrolusite,  ferrous  iron  is  con- 
verted to  the  ferric  condition ;  moreover,  the  silicate  of  manganese 
has  a  violet  or  pink  color,  and  so  helps  to  neutralize  the  green.  Only 
a  very  small  percentage  of  pyrolusite  should  be  thus  used.  The 
remedy  is  not  a  permanent  one,  however,  and  if  the  glass  is  exposed 
to  the  sunlight  for  a  long  time,  it  develops  a  violet  shade,  as  may 
often  be  observed  in  the  window  panes  of  old  houses. 

*  Lehrbuch  der  technischen  Chemie,  H.  Ost,  202. 
t  Chemical  Technology,  Wagner,  608. 


168  OUTLINES  OF  INDUSTRIAL   CHEMISTRY 

Arsenious  acid  (As203),  or  nitre  (KN08),  is  often  added  to  the 
materials  for  white  glass.  The  former  is  reduced  to  metallic 
arsenic,  which  volatilizes.  It  affords  a  very  clear  and  lustrous 
glass.  Zinc  oxide  is  often  used  to  decompose  any  sodium  sulphide, 
which  would  give  a  yellow  tinge  to  the  product. 

In  common  bottle  glass  and  other  cheap  grades,  where  color  is 
no  objection,  a  large  amount  of  blast  furnace  slag  is  often  used. 
This  generally  needs  the  addition  of  soda,  to  render  it  more  fusible 
and  plastic. 

The  formulae  for  glass  mixtures  vary  much  in  the  different  fac- 
tories, not  only  because  of  variations  in  the  composition  of  the  glass 
produced,  but  also  because  the  materials  are  of  different  degrees 
of  purity.  In  most  cases  these  are  empirical  recipes,  not  based  on 
analysis  of  the  raw  materials. 

The  fuel  for  glass  making  is  an  important  item.  A  quick  burn- 
ing material,  yielding  a  long  flame,  without  smoke  or  soot,  is 
desirable.  For  very  fine  grades,  wood  is  still  employed  in  some 
places,  but  good  coal  is  now  the  most  common.  In  this  country  the 
discovery  of  natural  gas  had  a  great  influence  on  the  glass  industry, 
and  within  a  few  years  most  of  the  larger  plants  were  moved  into 
the  gas  territory,  Pittsburg  becoming  the  centre  of  the  manufacture. 
With  the  decline  of  the  natural  gas  supply,  producer  gas  (see  p.  30) 
or  oil  has  been  substituted  as  fuel.  Gas  is  an  ideal  fuel  for  this 
purpose,  since  it  is  clean,  easily  managed,  and  gives  a  regular  heat. 
It  is  generally  employed  in  regenerative  furnaces  (Fig.  19,  p.  32). 
Crude  petroleum,  or  the  residuum  from  kerosene  distillation,  is  now 
much  used  and  is  a  good  fuel.  Whatever  the  mode  of  heating,  only 
the  flame  and  hot  gases  should  come  in  contact  with  the  pots  or 
their  contents. 

There  are  several  forms  of  glass-furnaces.  The  common  pot 
furnace  has  the  pots  placed  in  a  circle  around  a  central  opening 
in  its  bed,  through  which  the  flame  and  hot  gases  come  up  from  the 
grate,  which  is  below  the  hearth.  The  furnace  is  roofed  with  a 
rather  flat  arch,  which  deflects  the  flame  down  upon  and  around  the 
pots.  When  open  pots  are  used,  it  is  essential  that  no  soot  or  smoke 
enter  the  furnace,  and  much  care  is  necessary  in  firing.  In  some 
forms,  the  fuel  is  introduced  by  mechanical  means  from  beneath 
the  grate,  so  that  the  fire  burns  on  top  of  the  pile  of  coal.  This 
prevents  the  entrance  of  cold  air  into  the  furnace,  and  also  consumes 
all  smoke. 

The  Boetius  furnace  (Fig.  60)  is  much  used  abroad,  and  is  best 
adapted  for  closed  pots.  Coal  or  coke  is  charged  at  (A),  and  air 


GLASS 


169 


enters  through  (B,  B).  The 
flame  passes  through  (C)  into 
the  upper  compartment  (D), 
containing  the  pots.  The  prod- 
ucts of  combustion  escape 
through  (E,  E). 

Siemens  gas  furnace  (Fig. 
19,  p.  32)  is  much  used  be- 
cause of  its  economy  of  fuel, 
both  as  a  pot  furnace  and  as  a 
tank-furnace.  The  last  named 
is  more  economical  where  a 
large  quantity  of  one  kind  of 

glass  is  to  be  made.  It  replaces  the  expensive  and  fragile  pots 
by  a  single  large  deep  hearth  or  tank,  at  one  end  of  which  the 
raw  materials  are  continually  introduced,  while  the  glass  is  with- 
drawn at  the  other.  Figure  61  shows  a  plan  and  elevation  of  a  tank- 
furnace,  in  which  the  batch  is  introduced  at  (A).  The  gas-flame 
issues  from  (C,  C)  and  plays  over  the  surface  of  the  charge.  The 


FIG.  60. 


r    ff    f?    fr 


FIG.  61. 

batch  (B)  soon  fuses  and  the  liquid  mass  flows  towards  the  opposite 
end  of  the  tank.  At  (F)  are  elliptical  "floaters"  of  fire-clay,  one 
end  of  which  rests  in  recesses  in  the  wall,  while  the  free  ends  meet 
in  the  middle  of  the  furnace.  The  current  of  melted  glass  flowing 
towards  (D),  constantly  presses  these  floaters  together  and  prevents 
their  separation.  The  liquid  mass  thus  passes  under  the  floaters  and 
collects  in  the  compartment  (D),  from  which  it  is  withdrawn  through 


170 


OUTLINES   OF  INDUSTRIAL   CHEMISTRY 


the  openings  (E,  E).  At  (B)  the  temperature  is  very  high,  and  as 
the  glass  flows  slowly  towards  (F),  the  refining  takes  place.  In  (D) 
the  temperature  is  lower  and  the  glass  has  cooled  sufficiently  for 
working.  The  impurities,  rising  to  the  surface  during  the  melting 
and  refining,  are  retained  by  the  floaters  so  that  the  glass  in  (D)  has 
a  clean  surface  and  is  free  from  bubbles.  Small  rings  of  fire-clay 
may  be  kept  floating  on  the  glass  near  the  working  doors  (E,  E) ;  by 
dipping  the  glass  from  the  centre  of  these  rings,  it  is  obtained  free 
from  any  impurities  which  may  be  on  the  surface  of  the  melt  in  (D). 
A  typical  furnace  of  this  kind  may  be  about  75  feet  long  by  16  feet 
wide  and  5  feet  deep,  to  the  level  of  the  doors  (E,  E). 

Glass-furnaces  must  be  made  from  very  refractory  materials. 
The  dome  and  arches  are  usually  silica,  or  Dinas  bricks,  or  ganister, 
but  the  bed  is  generally  fire-clay,  as  this  is  less  attacked  by  the  con- 
tents of  a  pot  when  one  breaks.  The  life  of  a  furnace  is  very 
uncertain,  but  may  be  several  years.  If  allowed  to  cool,  it  is 
generally  necessary  to  reline  it  before  starting  again. 

Pots  for  glass  making  are  very  carefully  constructed,  only  the 
best  material  being  used.  The  breaking  of  a 
pot  in  the  furnace  is  a  serious  matter,  often 
resulting  in  the  loss  of  the  glass  and  possible 
extinguishing  of  the  fire;  and,  in  any  case, 
there  is  more  or  less  loss  of  time. 

Glass-pots  are  of  two  kinds,  open  and  closed. 
Open  pots  (Fig.  62)  are  circular  vessels,  about 
as  wide  as  they  are  deep,  i.e.  from  3  to  5  feet, 
and  usually  slightly  broader  at  the  top  than  on 
the  bottom.  They  are  preferred  for  a  quick 
melt,  and  are  generally  used  for  glass  which  contains  no  lead. 

Closed  pots  (Fig.  63)  are  usually  longer  in  one  direction,  and  are 
about  5  feet  by  3J 
feet,  by  4  feet  high. 
The  neck  of  the  open- 
ing is  built  into  the 
wall  of  the  furnace  in 
such  a  manner  that 
neither  flame  nor  fire 
gases  can  come  into 
contact  with,  and  in-  Fm  ^ 

jure    the    glass,    and 

consequently  cheaper  fuel  may  be  used ;  but  these  pots  heat  more 
slowly  than  do  open  ones.  They  are  always  used  for  lead  glass. 


FIG.  62. 


GLASS  171 

* 

Clay  rings  are  sometimes  placed  in  the  pots,  so  that  the  glass 
may  be  withdrawn  without  contamination  from  the  floating  impuri- 
ties. Sometimes  a  partition  is  constructed  across 
the  pot  (Fig.  64),  the  raw  materials  being  intro- 
duced and  melted  on  one  side,  and  the  refined 
glass,  free  from  impurities,  having  passed  under 
the  partition,  is  worked  out  on  the  other  side. 

The  material  of  the  pots  is  fire-clay ;  but  the 
necessary  degree  of  plasticity,  with  the  required 
infusibility,  are  possessed  but  by  few  clays.  To 
avoid  excessive  shrinkage  when  the  new  pot  is 
heated,  a  large  proportion  of  burned  clay  from  old  pots,  entirely  free 
from  any  adhering  glass  and  ground  to  a  coarse  powder,  is  mixed 
with  the  new  clay.  The  mass  is  then  moistened  and  well  kneaded  by 
treading,  and  is  then  allowed  to  stand  and  "  age  "  for  a  long  time,  to 
increase  the  plasticity.  The  pots  are  built  up  by  hand,  the  bottom 
being  formed  first,  and  the  sides  constructed  on  it.  The  clay  is  laid 
on  in  small  lumps,  and  each  lump  is  carefully  pressed  into  place  by 
the  workman  before  another  is  added.  From  three  to  five  inches  is 
usually  added  to  the  height  of  the  pot  each  day.  When  finished,  it 
is  allowed  to  stand  in  a  room  at  constant  temperature  and  protected 
from  draughts  of  air,  for  several  months,  to  dry  thoroughly.  In 
order  to  prevent  too  rapid  drying,  which  might  cause  cracking,  it  is 
generally  covered  with  canvas  or  paper  for  the  first  few  weeks. 

Before  placing  it  in  the  glass-furnace,  a  new  pot  is  heated  very 
slowly  in  a  special  furnace,  until  it  is  brought  up  to  the  temperature 
of  the  former,  into  which  it  is  then  transferred,  while  still  hot, 
through  an  opening  in  the  wall.  The  wall  must  be  taken  down,  the 
broken  pot  removed,  and  the  new  one  introduced,  without  allowing 
the  furnace  to  cool ;  hence  the  operation  is  difficult,  and  requires 
much  skill  on  the  part  of  the  workmen.  Once  introduced,  a  pot  is 
kept  in  constant  use,  and  never  allowed  to  cool;  for,  if  it  should,  it 
would  crack  when  heated  again.  Its  life  is  very  uncertain,  but  a 
good  one  will  sometimes  last  for  months.  The  first  charge  in  a  new 
pot  is  broken  glass  (cullet),  which  forms  a  glaze  over  the  surface, 
and  protects  it  from  the  solvent  action  of  the  melted  raw  materials. 

The  general  process  of  glass  making  is  as  follows :  The  finely 
ground  raw  materials  are  very  thoroughly  mixed,  sometimes  by 
regrinding  the  mixture  or  "  batch."  The  batch  is  shovelled  into  the 
pot,  together  with  a  certain  amount  of  broken  glass  called  "  cullet " ; 
this  melts  at  a  comparatively  low  temperature,  and  thus  assists  in 
liquefying  the  rest  of  the  charge.  More  of  the  batch  is  added,  until 


172 


OUTLINES  OF   INDUSTRIAL   CHEMISTRY 


the  pot  is  filled  to  the  desired  height  with  the  fused  mass;  then 
volatile  substances,  such  as  arsenious  acid,  used  in  decolorizing  the 
glass,  are  added. 

During  the  melting,  much  gas  (C02,  S02,  and  0)  escapes,  and  the 
bubbles  rise  through  the  melt,  stirring  it  and  causing  frothing.  A 
considerable  amount  of  the  alkali  and  other  constituents  volatilize. 
The  reactions  involved  are  variously  written  by  different  authorities  : 


(a)   1)  Na2C03  +  CaCO3  +  2  Si02  =  Na,Ca  (Si03)2  + 


C02  * 


2)  2  Na2S04  +  2  Si02  +  C  =  2  Na2Si03  •+  C02  +  2  SO 


C02  * 


3)  Na2Si03  +  CaC03  +  Si02  -  Na2Ca  (Si03)2 
(b)  2  Na*S04  +  6  Si02  +  0=2  (Na20,  3  SiOa)  +  2  S02  -f  C02.t 


When  the  melt  has  come  to  a  state  of  quiet  fusion,  the  temper- 
ature is  generally  raised  somewhat,  and  the  liquid  glass  allowed  to 
stand  for  a  time.  This  is  called  "  refining1,"  and  its  object  is  to  form 
a  homogeneous  mass,  free  from  bubbles  and  bits  of  uncombined 
silica  or  other  matter.  The  scum  which  collects  is  skimmed  off  ;  it 
is  called  "  glass  gall,"  and  consists  of  undecomposed  sulphates  and 
chlorides  of  lime  and  alkali,  alumina  compounds  from  the  pot,  and 
various  other  impurities.  If  too  little  carbon  is  used  in  the  batch, 
the  melt  is  covered  with  a  layer  of  fused  sodium  sulphate  ;  this  is 
known  to  the  workmen  as  "  salt  water."  Samples  of  the  glass  are 
examined  during  the  refining,  and  these  determine  the  exact  time  of 
heating.  After  refining,  the  glass  is  too  liquid  to  blow,  or  to  work 
to  advantage,  and  is  cooled  until  it  becomes  pasty. 

The  quantities  of  materials  used  in  the  batch,  for  some  typical 
glasses,  are  shown  in  the  following  table  :  — 


SiO2 

Na2C03 

Na2S04 

CaCO3 

CaO 

Mn02 

Pb304 

K2C03 

Coke 

Slag 

French  Plate 

100 

34 



14.5 



0.25 









(Soda-lime) 

Bohemian 

100 

— 

— 

— 

18 

— 

— 

40 

— 

-4-" 

(Potash-lime) 

Window 

100 

5 

37.5 

35.8 

— 

0.4 

— 

— 

4 

— 

(Soda-lime) 

Lead  flint 

100 

— 

— 

— 

— 

— 

60 

20 

— 

— 

Bottle  glass 

100 

— 

25. 

34 

— 

— 

— 

— 

3 

5 

(Green  glass) 

*  Wagner,  Chemical  Technology,  608. 

t  Ost,  Lehrbuch  d.  technischen  Chemie,  202. 


GLASS  178 

Glass  is  known  under  various  names  in  commerce,  according  to 
the  method  of  its  manufacture  or  the  uses  to  which  it  is  put;  for 
example,  plate,  crown,  and  window  glass. 

Plate  glass  is  cast  on  a  large  iron  plate  or  "  casting  table,"  made 
up  of  thick,  narrow  segments  of  cast  iron,  bolted  together  and 
planed  on  top.  These  tables  were  formerly  cast  in  one  piece,  and, 
being  large  and  thick,  were  very  expensive.  But  when  put  to  use, 
they  soon  became  warped  and  dished,  owing  to  unequal  expansion 
of  the  top  and  bottom ;  this  caused  much  loss  of  time  and  glass  in 
the  subsequent  grinding  of  the  plate.  The  built-up  plate  is  much 
cheaper  and  retains  its  even  surface  much  longer. 

The  melted  glass  is  poured  on  the  table  and  spreads  out  in  an 
even  layer.  But  to  give  the  plate  a  uniform  thickness  and  to 
smooth  down  any  inequalities  of  the  surface,  a  heavy  iron  roller, 
travelling  on  adjustable  guides  at  the  edge  of  the  table,  is  passed 
over  it.  The  height  of  these  guides  determines  the  thickness  of  the 
plate.  Both  the  casting  table  and  the  roller  are  heated  before  use, 
so  that  the  glass  may  not  be  cooled  too  rapidly.  As  soon  as  the 
plate  is  rolled,  it  is  transferred  to  the  floor  of  the  annealing  furnace, 
which  is  directly  in  front  of  the  casting  table,  and  which  has  been 
heated  to  the  temperature  of  the  glass.  The  annealing  oven  is  then 
closed  tightly  and  the  fire  drawn,  leaving  the  plate  to  cool  very 
slowly  for  a  number  of  days.  All  glass  must  be  annealed.  This 
process  probably  allows  the  molecules  to  arrange  themselves  so  that 
there  is  no  considerable  internal  stress  when  the  mass  is  cold. 
Unannealed  glass,  which  has  been  suddenly  cooled,  is  always  under 
high  internal  strain,  which  makes  it  exceedingly  brittle,  and  may  even 
cause  it  to  fly  to  pieces  spontaneously,  or  when  slightly  scratched. 

When  removed  from  the  annealing  furnace,  the  plate  is  uneven 
and  rough,  and  may  be  somewhat  devitrified  on  the  surface.  It  is 
fastened  on  a  horizontal  table,  and  heavy  cast-iron  rubbers  are  made 
to  slide  over  its  surface  with  a  rotary  motion,  while  coarse  sand  and 
water  are  sprinkled  on  it.  When  the  glass  is  smoothed  and  of  a 
uniform  thickness,  it  is  polished  by  rubbing  with  buffers,  covered 
with  leather  or  felt,  and  used  with  fine  emery  dust  or  putty  powder. 
About  one-half  of  the  thickness  of  the  plate  is  cut  away  during  the 
grinding  and  polishing. 

Plate  glass  is  usually  a  soda-lime  glass.  The  batch  is  melted 
and  refined  as  has  been  described,  great  care  being  taken  to  remove 
all  the  "  gall,"  which  is  skimmed  off  immediately  before  the  casting. 
An  especially  strong  pot  is  used,  which  will  stand  the  strain  of  lift- 
ing from  the  furnace  while  full  of  melted  glass.  The  furnace  is 


174  OUTLINES  OF  INDUSTRIAL   CHEMISTRY 

constructed  with  brick-lined,  cast-iron  doors,  which  open  to  permit 
the  removal  of  the  pot.  The  melting  and  annealing  furnaces  are 
often  joined,  so  that  the  latter  may  be  heated  with  waste  heat. 
Sometimes  several  plates  are  annealed  at  one  time. 

The  chief  uses  of  plate  glass  are  for  windows  and  mirrors. 
A  Considerable  quantity  of  "  rough  plate,"  unground,  as  it  comes 
from  the  annealing  furnace,  is  used  for  skylights  and  for  flooring. 

Window  glass  is  always  blown.  It  is  usually  a  soda-lime  glass, 
and  the  batch  is  melted  and  refined  in  the  usual  manner,  either  in 
pots  or  in  tanks.  After  the  refining,  the  glass  is  allowed  to  become 
pasty,  and  then  the  blower  begins  his  work.  His  chief  tool  is  the 
"  pipe,"  a  straight  piece  of  iron  tubing,  four  or  five  feet  long,  usually 
provided  with  a  mouthpiece.  He  dips  the  pipe  into  the  soft  glass, 
which  is  called  "  metal,"  and  gathers  a  lump  on  the  end.  Then,  by 
blowing  through  the  pipe,  while  whirling  it  between  the  palms  of 
his  hands,  he  forms  a  hollow  globe  of  glass.  This  is  re-heated  in  a 
special  furnace  ("  glory-hole  ")  until  soft,  rolled  on  a  flat  surface,  and 
then  swung  in  a  vertical  circle,  with  occasional  blowing  through  the 
pipe,  until  the  globe  has  elongated  into  a  hollow  cylinder,  closed 
at  one  end  and  opening  into  the  pipe  at  the  other.  In  order  to  have 
plenty  of  room  for  the  vertical  swinging,  the  workman  stands  on 
a  plank  or  bridge  placed  across  a  rather  deep  pit.  The  closed  end 
of  the  cylinder  is  re-heated  until  soft,  and  then  blown  out ;  the 
small  opening  thus  made  is  enlarged  by  means  of  the  "  widening 
tongs."  The  pipe  is  detached  by  touching  its  point  of  attachment 
with  a  wet  stick,  and  the  edges  of  the  still  soft  glass  are  trimmed 
with  shears.  A  hollow  cylinder,  open  at  both  ends,  is  thus  formed, 
and  is  cut  lengthwise  with  a  diamond.  It  is  then  put  into  the  flat- 
tening furnace,  in  such  a  position  that  the  cut  is  on  the  upper  side. 
The  heat  being  sufficient  to  soften  the  glass,  the  cylinder  slowly 
opens,  and  spreads  out  on  the  floor  of  the  furnace  in  a  flat  sheet.  It 
is  then  transferred  to  the  annealing  furnace  for  blown  ware.  This 
consists  of  a  long  oven,  heated  at  one  end  and  cool  at  the  other.  A 
system  of  endless  iron  bands  carries  the  glass  slowly  from  the  hot 
to  the  cool  end  of  the  oven.  Sometimes  the  glass  to  be  annealed  is 
placed  on  a  large  horizontal  table,  usually  built  of  slabs  of  stone, 
and  carefully  balanced,  so  as  to  revolve  easily  and  slowly,  by  means 
of  a  gear,  while  a  segment  passes  through  a  narrow  opening  in  the 
side  of  the  flattening  furnace,  where  it  is  exposed  to  the  high  tem- 
perature. The  glass  is  thus  slowly  carried  out  of  the  furnace  into 
a  cooler  compartment,  from  which  it  is  removed  when  nearly  cold. 
This  table  is  chiefly  used  for  window  glass. 


GLASS         §  175 

The  glass  sheets  are  now  cut  to  marketable  size,  without  any  pol- 
ishing. Since  the  surface  of  blown  glass  is  fused  and  not  polished, 
it  is  brilliant  and  hard.  Consequently,  it  is  less  easily  scratched  or 
etched,  and  is  more  durable  than  plate  glass  when  exposed  to  the 
weather. 

Glass-blowing  is  an  exceedingly  fatiguing  labor,  and  only  men  of 
strong  constitution  and  good  lung  power  can  do  it.  The  mass  of 
glass  which  a  good  workman  will  handle  at  one  time  averages  about 
18  pounds,  and  from  it  he  will  form  a  cylinder  over  a  yard  long  and 
a  foot  in  diameter. 

Crown  glass  is  a  form  of  blown  glass,  in  which  the  globular  bal- 
loon first  blown  is  flattened  by  pressing  against  a  flat  surface.  The 
end  of  an  iron  rod  is  smeared  with  a  coating  of  melted  glass,  and 
attached  to  the  centre  of  the  flattened  surface.  The  pipe  is  then 
detached,  leaving  a  small  hole.  By  re-heating  and  rotating  the  rod 
swiftly  about  its  longitudinal  axis,  the  balloon  opens  out,  forming  a 
circular  plate  or  disk,  with  the  rod  at  the  centre.  Disks  4  or  5  feet 
in  diameter  are  thus  made.  But  they  are  not  of  the  same  thickness 
at  the  edge  and  middle;  where  the  rod  was  attached,  there  is  a 
thick  rounded  mass  called  the  "  bull's-eye."  This  must  be  cut  out, 
so  large  window  panes  cannot  be  made  from  crown  glass.  Thus  it 
is  not  an  economical  form  of  glass-blowing,  and  the  industry  is  prac- 
tically abandoned.  A  little  is  now  made  to  supply  a  small  demand 
for  the  "bull's-eyes"  for  decorative  purposes.  Crown  glass  has  a 
very  brilliant  surface. 

A  skilful  glass-blower  can  form  all  kinds  of  glass  utensils  by 
the  use  of  his  pipe  and  other  tools.  Wine  glasses,  tumblers,  bottles, 
and  lamp  chimneys,  for  example,  are  often  entirely  blown.  But 
much  glass  ware  is  now  blown  in  moulds,  or  pressed. 

In  cut-glass  ware,  the  design  is  cut  in  the  solid  glass,  which  has 
been  given  its  general  form  by  blowing  or  pressing.  Sometimes  the 
design  is  formed  in  the  pressed  ware,  and  the  surface  only  is  cut 
and  polished.  Glass-cutting  is  done  on  a  soft  steel,  copper,  or  sand- 
stone wheel,  the  cutting  edge  of  which  is  fed  with  sand  or  emery 
and  water.  The  polishing  is  done  on  similar  wheels  of  wood,  fed 
with  rouge  or  putty  powder.  Lead  glass  is  nearly  always  used  for 
cutting,  since  it  is  softer  and  more  brilliant  than  other  varieties. 

Pressed  glass  is  made  by  the  use  of  a  die  or  mould ;  these  moulds 
are  quite  expensive,  but  owing  to  the  great  number  of  pieces  of  the 
same  form  and  design  that  are  made  with  slight  labor,  pressed  ware 
is  fairly  cheap. 

"  Tough "  or  "  tempered  "  glass  is  produced  by  a  special  method 


176  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

of  annealing,  the  articles  so  treated  being  capable  of  withstanding 
blows  and  sudden  changes  of  temperature.  This  tempering  is  done 
by  plunging  the  article,  while  still  so  hot  as  to  be  somewhat  soft, 
into  a  bath  of  oil  heated  to  100°-300°  C.  This  sudden  "  quenching  " 
hardens  the  surface  of  the  glass,  but  causes  internal  stresses.  If 
scratched  or  cut  slightly,  toughened  glass  is  very  apt  to  fly  to  pieces, 
sometimes  with  great  violence.  And  even  after  standing  a  long 
time  spontaneous  fracture  often  occurs.  It  is  mainly  used  for  lamp 
chimneys. 

A  process  for  making  hardened  glass  plates  and  window  lights  is 
employed,  in  which  cold  metallic  surfaces  are  applied  to  the  glass 
plates  while  the  latter  are  still  plastic.  The  sudden  chilling 
imparts  an  exceedingly  hard  surface  to  the  glass,  so  that  it  can 
be  used  in  exposed  situations,  such  as  in  street  lamps. 

A  compound  glass  is  a  recent  invention  to  replace  the  hardened 
or  tempered  glass.  Articles  are  formed  of  two  layers  of  glass,  the 
inner  layer  having  a  low  coefficient  of  expansion  while  the  outside 
layer  has  a  high  coefficient.  This  glass  is  particularly  recommended 
for  lamp  chimneys  and  chemical  vessels  which  must  endure  sudden 
changes  of  temperature.  The  ratio  between  the  two  coefficients 
must  be  very  carefully  maintained. 

Colored  glasses  are  produced  by  adding  to  the  ordinary  batch  cer- 
tain metallic  oxides  or  salts,  or  even  finely  pulverized  metal.  These 
dissolve  in  the  glass,  and  impart  a  characteristic  color. 

Green  glass  is  produced  by  the  use  of  ferrous  oxide,  chromic 
oxide,  or  a  mixture  of  cupric  and  ferric  oxides.  The  color  produced 
by  ferrous  oxide  is  a  dull  green,  of  no  particular  beauty.  Copperas 
or  iron  filings  are  generally  used  in  the  batch  of  melted  glass  to  form 
the  ferrous  silicate  necessary  for  the  color.  Chromic  oxide  (Cro08) 
imparts  a  better  green.  It  is  usually  produced  by  adding  potassium 
bichromate  (K2Cr207)  to  the  batch.  If  an  excess  of  chromium  oxide 
is  present,  the  uncombined  portion  separates  as  minute  crystals, 
disseminated  through  the  glass,  producing  chrome  aventurine.  A. 
mixture  of  cupric  and  ferric  oxides  produces  green  glass,  owing  to 
the  combined  effect  produced  by  these  oxides  individually. 

Yellow  glass  is  made  by  adding  sulphur  or  carbonaceous  matter 
to  the  batch,  producing  sodium  or  potassium  sulphides,  which  color 
the  glass.  A  common  method  is  to  introduce  wood  or  charred  horn 
into  the  melted  glass.  Cadmium  sulphide  is  sometimes  employed. 
No  sulphur  compound  can  be  used  with  lead  glass.  A  rich  yellow 
stain  is  obtained  by  the  use  of  metallic  silver  or  silver  chloride; 
this  is  much  used  in  making  church  windows,  and  was  known  in 


GLASS  177 

the  Middle  Ages.  A  peculiar  greenish  yellow,  fluorescent  glass  is 
produced  with  uranium  oxide,  but  it  is  expensive. 

Orange  glass  of  various  shades  is  made  by  adding  selenium  (as  a 
selenate  with  a  reducing  agent),  or  a  mixture  of  ferric  oxide  and 
manganese  dioxide. 

Blue  glass  is  made  with  cobaltic  oxide  (Co203)  or  cupric  oxide.  A 
very  small  percentage  (0.1)  of  cobaltic  oxide  produces  a  deep  blue 
color.  If  more  than  5  per  cent  is  used,  the  color  is  so  deep  that  the 
glass  may  be  ground  for  pigment  (smalt).  Owing  to  the  intensity 
of  its  color,  cobalt  glass  is  much  used  for  "  flashing  "  on  the  surface 
of  white  glass.  To  do  this,  the  blower  dips  his  pipe  into  the  pot  of 
colored  glass,  and,  collecting  a  small  lump,  dips  it  into  the  pot  of 
colorless  glass,  or  vice  versa.  By  blowing  he  forms  a  sheet  of  colorless 
glass  which  is  coated  on  one  side  with  a  very  thin  layer  of  colored 
glass,  both  firmly  welded  together.  Both  glasses  must  have  the  same 
composition  and  the  same  coefficient  of  expansion.  A  light  blue 
(sky-blue)  is  obtained  by  the  use  of  a  small  quantity  of  cupric  oxide. 

Violet  is  produced  by  a  small  amount  of  pyrolusite,  free  from 
iron.  An  excess  of  manganese,  especially  if  much  iron  is  present, 
gives  a  deep  yellow  or  brown. 

Red  glass  is  made  with  metallic  copper,  cuprous  oxide,  or  metallic 
gold.  Copper  gives  a  deep  ruby  red,  but  gold  yields  a  bluish  red, 
which  is  more  brilliant.  For  copper  ruby  the  form  of  cuprous  oxide 
(Cu2O2),  called  "hammer-scale,"  is  used.  A  small  quantity  of  iron 
filings,  or  stannous  oxide,  is  often  added  to  reduce  any  cupric  oxide, 
The  glass  obtained  from  the  melt  for  copper  ruby  is  nearly  colorless, 
or  a  pale  green.  By  a  second  careful  reheating  in  a  muffle,  the 
deep  ruby  color  is  slowly  developed.  It  is  so  intense  that  the  glass 
is  used  for  "  flashing." 

Gold  ruby  is  produced  in  much  the  same  way  as  copper.  Usually 
a  small  quantity  of  gold  chloride  is  added  to  the  batch  before  melt- 
ing. On  cooling,  the  glass  is  colorless,  or  reddish  yellow ;  the  ruby 
color  appears  on  reheating.  Great  care  is  necessary,  for  if  over- 
heated the  color  may  change  to  a  dull  red  brown.  A  very  minute 
quantity  of  gold  is  sufficient  to  color  the  glass  deeply.  Gold  ruby 
is  also  used  for  flashing. 

White,  "opal,"  or  "milk"  glass  is  made  by  adding  cryolite  or 
fluorite,  with  felspar,  to  the  batch  for  common  glass.  Calcium 
phosphate,  as  bone-ash,  may  also  be  used.  These  substances  crys- 
tallize in  the  glass  when  the  melt  is  kept  near  its  fusion  point  for 
some  time,  and  thus  cause  the  opalescence.  Large  quantities  of  tin 
or  zinc  oxides  produce  a  translucent  milk  glass. 


178  OUTLINES  OF   INDUSTRIAL   CHEMISTRY 

Black  glass  is  obtained  by  using  a  large  excess  of  pyrolusite,  iron, 
or  copper  oxides.  The  so-called  "smoked  glass,"  used  for  optical 
purposes,  contains  some  nickel. 

Enamel  is  an  easily  fusible  glass,  usually  containing  lead  and 
boric  acid,  or  phosphate  or  stannate  of  sodium  or  potassium.  It  is 
usually  white,  blue,  or  gray,  the  color  being  produced  by  adding 
proper  oxides.  It  is  used  for  coating  metallic  (iron)  vessels,  pottery, 
(tiles,  flower-pots,  bricks,  etc.),  and  porcelain.  For  cooking  vessels 
it  must  be  free  from  lead,  and  is  composed  of  sand,  borax,  soda, 
and  calcium  phosphate  or  white  clay  (kaolin). 

Enamel  must  have  a  coefficient  of  expansion  about  equal  to  that 
of  the  iron  on  which  it  is  placed,  otherwise  the  glaze  is  soon  de- 
stroyed by  heating  and  cooling. 

Iridescent  glass  is  made  by  exposing  the  hot  glass  to  the  vapors 
of  stannic  chloride  (SnCl4),  or  hydrochloric  acid.  These  vapors 
attack  the  surface  of  the  glass  and  alter  its  composition.  It  was 
formerly  supposed  that  the  art  of  making  this  glass  was  invented 
by  the  Romans,  and  later  was  lost.  However,  the  old  Roman  glass 
was  not  originally  iridescent,  but  has  become  so  through  expos- 
ure to  dampness  and  carbon  dioxide.  The  surface  has  been  partly 
decomposed,  the  alkali  dissolving,  thus  producing  a  thin  layer  of 
glass  having  a  different  composition  and  physical  structure  from  the 
main  body.  This  thin  film  causes  interference  of  the  light  rays  and 
produces  a  play  of  colors  when  viewed  in  different  positions. 

Mirrors  were  formerly  coated  with  an  amalgam  of  tin.  Tin  foil 
was  covered  with  mercury,  and  the  glass,  carefully  cleaned,  was 
laid  on  the  amalgam,  excess  of  mercury  being  forced  out  at  the 
sides,  and  the  amalgam  adhering  firmly  to  the  glass. 

But  the  silver  mirror  is  now  the  only  kind  made.  A  coating  of 
metallic  silver  is  deposited  on  the  glass  from  an  ammoniacal  solu- 
tion of  silver  nitrate  by  the  use  of  a  reducing  agent.  Ammonium 
tartrate,  or  a  solution  of  glucose  or  milk  sugar  in  caustic  soda,  is 
generally  used  for  this  purpose;  or  aldehyde  is  sometimes  used. 
The  glass  is  carefully  cleaned  and  covered  with  the  silver  solution 
containing  the  reducing  substance,  and  heated  gently  on  a  steam  or 
hot  air  bath.  The  thin  layer  of  metallic  silver  deposited  adheres  to 
the  glass,  and  is  washed  and  dried,  and  covered  with  a  protecting 
varnish  to  prevent  the  hydrogen  sulphide  in  the  air  from  tarnishing 
the  reflecting  surface. 

Plate  glass  is  generally  used  for  the  best  mirrors.  Blown  glass, 
which  is  used  for  the  cheaper  ones,  is  very  apt  to  contain  bubbles 
and  striae,  causing  distortion  of  the  image. 


GLASS  179 

Tradition  assigns  the  discovery  of  glass  to  the  Phoenicians. 
Glass  making  is  a  very  old  industry,  and  was  known  to  the  early 
Egyptians,  since  glass  beads  have  been  found  in  mummy  cases  at 
least  3000  years  old.  Glass  articles  have  also  been  found  in  the  ex- 
cavations at  Nineveh.  From  Egypt,  the  industry  was  transferred  to 
Rome,  and  on  the  fall  of  the  Western  Empire  the  art  was  carried  to 
Byzantium.  Byzantine  glass  attained  a  high  degree  of  perfection ; 
but  in  the  middle  of  the  thirteenth  century  Venice  became  the  cen- 
tre of  the  industry,  and  Venetian  glass-blowers  were  remarkably 
expert  in  the  production  of  beautiful  and  delicate  patterns.  Finally, 
Bohemia  took  the  lead  in  the  manufacture  of  glass,  and  has  retained 
a  front  rank  ever  since. 

Window  glass  was  made  by  the  Romans  to  a  small  extent,  and 
specimens  of  such  glass  were  taken  from  the  ruins  of  Pompeii.  In 
England,  it  first  came  into  use  in  houses  during  the  reign  of  Eliza- 
beth, but  previously  to  this  it  had  been  used  in  cathedrals  and 
churches.  From  the  records  of  York  cathedral,  it  is  shown  that 
during  the  time  of  Archbishop  Wilfrid  (669-709  A.D.)  "glass  was 
placed  in  the  windows  so  that  birds  could  no  longer  fly  in  and 
out  and  defile  the  sanctuary."  The  contract  for  the  glass  in  the 
great  West  Window,  given  by  Archbishop  Melton,  is  dated  1330. 
The  work  was  finished  before  1350,  and  the  price  paid  was  6  d.  per 
square  foot  for  white,  and  1  s.  per  square  foot  for  colored  glass. 
This  window  is  54  feet  high  by  30  wide,  and  is  to-day  regarded  as 
one  of  the  finest  examples  of  stained  glass  in  England.  The  great 
East  Window  (77  feet  high  and  32  feet  wide)  was  glazed  by  John 
Thornton  in  1405-1408,  for  which  he  received  4  s.  per  week.  These 
examples  demonstrate  the  high  degree  of  perfection  to  which  the 
glass  industry  had  advanced  during  the  Middle  Ages. 

At  the  present  time,  Belgium  and  England  lead  in  the  produc- 
tion of  window  and  plate  glass,  while  Germany,  France,  and  the 
United  States  also  manufacture  enormous  quantities.  Austria  and 
Germany  are  the  leading  producers  of  blown  ware. 

REFERENCES 

Glass  Making.    Powell,  Chance  and  Harris.     1883. 

TJ.  S.  Census,  1880.  — Report  on  the  Manufacture  of  Glass.    J.  D.  Weeks. 

Die  Glas-Fabrikation.     R.  Gerner,  Vienna,  1880.     (Hartleben.) 

Handbuch  der  Glas-Fabrikation.    Dr.  E.  Tscheuschner,  Weimar,  1885.    (Voigt.) 

Die  Fabrikation  und  Raffinirung  des  Glases.    Wilhelm  Mertens,  Vienna,  1889. 

(Hartleben.) 
Verre  et  Verrerie.    L.  Appert  et  Jules  Henrivaux,  Paris,  1894.     (Gauthiers- 

VillarsetFils.) 


180  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

Journal  of  the  Franklin  Institute.     1887.     Glass  Making.  —  C.  H.  Henderson. 
Proceedings  of  Engineers'  Society  of  Western  Pennsylvania.     1895,  119.    A 
Study  of  Glass.  —  Robert  Linton. 


CERAMIC    INDUSTRIES 

Clay  is  a  natural  hydrated  silicate  of  aluminum,  formed  by  the 
weathering  of  felspar  or  felspathic  rock,  such  as  granite.  When 
heated,  the  water  of  constitution  in  the  hydrated  silicates  is  driven 
off,  and  chemical  changes  are  brought  about  by  which  the  clay 
becomes  stone-like  in  its  hardness ;  and,  if  pulverized  again,  its 
plasticity  is  gone. 

Clays  which  have  not  been  transported  by  natural  waters  from 
the  place  where  they  were  formed  are  called  primary ;  secondary 
clays  are  those  which  have  been  washed  from  their  original  beds 
and  deposited  elsewhere.  Primary  clay  which  has  been  derived 
from  pure  felspar  contains  but  little  impurity  other  than  silica,  and 
is  called  kaolinite,  kaolin,  or  China  clay.  It  is  a  white,  powdery 
mass,  consisting  essentially  of  hydrated  silicate  of  aluminum,  nearly 
all  the  alkali  having  been  leached  out.  The  decomposition  of  a 
felspar  may  be  represented  by  the  following  equation :  — 

A1203,  K20,  6  Si02  +  C02  +  2"H20 

=  A1203,  2  Si02  •  2  H20  +  K2C03  +  4  Si02. 

But  since  felspars  and  granites  contain  mica  and  quartz  in  a 
greater  or  less  quantity,  these  are  generally  found  in  the  kaolin ;  if 
the  particles  are  too  coarse,  they  are  removed  by  levigating.  Pure 
kaolin  is  almost  infusible,  but  the  presence  of  impurities  increases  its 
fusibility  greatly.  Kaolins  are  generally  of  a  granular  or  crystalline 
structure,  and  do  not  form  a  very  plastic  mass  when  wet;  hence 
they  are  called  "  lean  "  clays.  When  burned,  they  yield  a  white  or 
nearly  white  pottery. 

Fire-clays  are  almost  infusible.  They  are  generally  found  under- 
lying coal  beds.  In  composition  they  are  kaolins,  containing  a  con- 
siderable amount  of  free  silica,  as  quartz.  They  may  contain  a  little 
more  iron  than  good  China  clay,  but  are  free  from  alkalies. 

Secondary  clay,  even  if  derived  from  pure  felspar,  generally 
contains  some  foreign  matter,  which  has  been  mixed  with  it  during 
its  transference  from  the  place  of  formation  to  the  point  of  deposit. 
Then,  too,  the  sharp  edges  of  the  crystalline  particles  have  been 
worn  off  by  their  rubbing  against  each  other  during  this  motion,  and 
the  clay  acquires  the  property  of  plasticity.  These  secondary  plastic 


CERAMIC   INDUSTRIES  181 

clays  are  called  pipe-  or  ball-clays,  and  are  also  known  as  "fat"  clays, 
to  distinguish  them  from  the  lean  or  non-plastic.  Fat  clays  absorb 
much  water  and  have  great  binding  power,  so  that  they  are  easily 
shaped  by  the  potter.  But  on  drying,  and  especially  when  burned, 
they  shrink  very  much.  This  shrinkage  is  counteracted  by  mixing 
with  the  fat  clay  a  certain  amount  of  "  leaning "  material,  such  as 
silica,  pulverized  burnt  clay,  or  "  grog,"  the  ground,  unglazed  body 
of  pottery.  Fat  clays  are  much  more  fusible  than  lean  clays. 

All  clays  have  a  peculiar  and  characteristic  odor  when  breathed 
upon  or  wet. 

The  preparation  of  clay  for  the  potter  is  quite  simple.  It  is 
mined,  and  allowed  to  weather  for  several  months,  which  is  said  to 
increase  its  plasticity.  Fine  clays  which  are  to  be  used  for  the 
better  grades  of  ware  are  then  thoroughly  "slipped"  with  water 
in  a  "  blunger  "  (a  vat  with  mechanical  stirrers),  and  thus  levigated. 
The  coarse  particles  of  quartz,  mica,  and  undecomposed  felspar  are 
thus  separated,  and  only  the  clay  substance,  with  a  very  little  finely 
divided  quartz,  remains  in  suspension.  The  fine  mud,  called  "  slip," 
obtained  by  settling  the  wash  .waters,  is  put  into  cloth  bags  and 
pressed,  or  it  is  run  through  a  filter-press.  It  is  then  ready  for  use. 
Clays  are  sold  under  the  names,  kaolin,  ball-  or  potter's-clay,  and 
fire-clay. 

The  most  important  properties  of  a  clay  from  the  potter's  stand- 
point are  its  plasticity,  fusibility,  and  contraction  when  burned. 
The  color  of  the  finished  product  is  very  important  when  making 
white  ware.  Plasticity  is  diminished  by  the  presence  of  rough  or 
sharp  particles  of  silica,  felspar,  or  other  material.  Fusibility  is 
important  as  determining  its  adaptability  to  the  manufacture  of 
certain  kinds  of  pottery  and  porcelain,  which  are  burned  at  a  very 
high  temperature.  If  the  clay  contains  much  iron  oxide,  lime, 
magnesia,  or  alkali,  it  is  more  fusible  than  if  pure. 

The  properties  of  a  clay  are  dependent  on  the  form  of  combina- 
tion of  its  constituents,  and  an  empirical  analysis  is  not  sufficient  for 
the  purpose  of  the  potter.  He  must  have  a  rational  analysis ;  that 
is,  he  must  know  the  proportions  of  clay  substance  (hydrated  silicate 
of  aluminum),  felspar,  quartz,  lime,  etc.,  present,  in  order  that  he 
may  add  the  proper  amount  of  those  ingredients  which  are  lacking 
to  give  a  mass  having  the  desired  properties.  The  following  are 
complete  analyses,  with  the  corresponding  rational  analyses  of 
certain  clays :  — 


182  OUTLINES  OF  INDUSTRIAL   CHEMISTRY 

CHEMICAL  ANALYSES 


GERMAN  * 

(SENNEWITZ). 

BOHEMIAN* 

CZM- 

VIRGINIAN  t 
(KAOLIN). 

Ouiot 
(.FIRE-CLAY). 

ENGLISH  t 
(CORNISH  STONE). 

SiO,  

46.8 

JtflVy. 

50  02 

74  93 

73  57 

ALA  .... 
Fe,03  .... 
CaO  

23.8 
0.8 

38.5 

1.1 

35.18 
0.36 
0  12 

17.19 
0.79 
0.29 

16.48 
0.27 
1.17 

MO-O 

0.5 

trac6 

0  07 

0  46 

0  21 

Alkalies.  .  .  . 
H20  

1.4 

8.4 

1.4 

12.9 

3.39 
10.57 

1.61 
5.44 

5.84 
2.45 

99.8 

100.7 

99.71 

100.71 

99.98 

RATIONAL   ANALYSES 


Clay  substance     . 

63.8 

96.6 

84.12 

48.24 

33.57 

Quartz   .     .     .     . 

35.5 

2.3 

6.55 

49.72 

41.10 

Felspar  .     . 

0.7, 

1.1 

9.04 

2.75 

25.31 

100.0 

100.0 

99.71 

100.71 

99.98 

From  these  it  will  readily  be  seen  that  clays  having  approxi- 
mately the  same  empirical  composition  may  differ  widely  in  fusi- 
bility, expansion,  and  in  the  porosity  of  the  burned  product.  Quartz, 
in  the  absence  of  bases  with  which  it  may  combine,  increases  the 
expansion  and  decreases  the  fusibility.  Felspar  makes  the  clay 
more  fusible,  acting  as  a  flux  on  the  silica  and  clay  substance.  It 
causes  vitrification  of  the  mass,  on  burning ;  and,  being  itself  non- 
plastic,  is  often  used  to  modify  a  too  plastic  clay. 

Ceramics  comprise  two  general  divisions :  (a)  articles  having  a 
non-porous  body,  and  (b)  articles  having  a  porous  body.  Non-porous 
ware  is  hard,  impervious  to  liquids  and  gases,  and  has  a  semi-vitrified 
appearance  on  the  fractured  surface.  It  is  burned  at  a  very  high 
temperature,  and  is  chiefly  made  from  kaolin,  with  just  enough 
plastic  material  to  enable  the  workman  to  form  the  desired  article. 
This  division  includes  porcelain  and  stoneware.  Porous  ware  is  less 
dense,  has  an  earthy  appearance  on  the  fractured  surface,  and  per- 
mits the  passage  of  gases  and  liquids  through  its  pores.  It  is  made 
from  plastic  clays,  and  burned  at  a  low  or  moderate  temperature. 
It  comprises  bricks,  terra  cotta,  common  crockery,  and  some  kinds 
of  stoneware. 

There  are  two  kinds  of  porcelain,  the  hard  and  the  soft,  or 
"  fritted."  Both  are  harder  than  glass,  and  very  resistive  to  chem- 
ical action. 

*  Lehrbuch  der  technischen  Chemie.    H.  Ost,  227. 
t  Chemistry  of  Pottery.    K.  Langenbeck,  10,  111,  165. 


CERAMIC   INDUSTRIES  183 

Hard  porcelain  softens  only  at  the  highest  attainable  tempera- 
ture, and,  when  burned,  forms  a  perfectly  homogeneous  mass,  which 
is  translucent.  The  body  is  composed  of  kaolin,  quartz,  and  felspar, 
in  definite  proportions.  It  is  glazed  with  pure  felspar,  or  a  mixture 
of  quartz  and  felspar,  with  sufficient  lime  to  form  a  difficultly 
fusible  glass.  This  glaze,  which  must  have  the  same  coefficient  of 
expansion  as  the  body,  is  very  perfectly  welded  on  to  the  body,  by 
a  second  burning  at  a  very  high  temperature ;  and  no  distinct  line 
of  demarkation  between  the  body  and  the  glaze  can  be  seen  on  a 
fractured  surface.  Berlin  and  Meissen  ware  are  examples. 

Soft  porcelain  consists  of  a  kaolin  body,  with  ball-clay,  bone-ash, 
and  felspathic  materials  added.  This  is  burned  at  a  high  tempera- 
ture, and  glazed  with  a  lead-boric-acid  glass,  which  is  fused  on  to  its 
surface  by  a  second  much  lower  heating.  The  glaze  does  not  pene- 
trate so  perfectly,  but  forms  a  more  superficial  layer  than  is  the  case 
with  hard  porcelain.  English  china,  Sevres  ware,  and  Japanese  thin 
ware  are  soft  porcelain. 

In  preparing  the  clay  for  porcelains,  the  powdered  materials  are 
thoroughly  mixed,  wet,  and  the  "  slip  "  kneaded  and  allowed  to  age 
for  several  months.  The  articles  are  formed  on  the  potter's  wheel, 
a  horizontal  revolving  table,  driven  by  foot  or  machine  power. 
Sometimes  the  slip  is  cast  in  porous  moulds  of  gypsum  or  burned 
clay,  which  absorb  the  water,  leaving  the  mud  on  the  face  of  the 
mould.  Or  the  partly  dried  mud  is  pressed  in  moulds  to  form  one 
surface  of  the  article,  the  other  being  completed  on  the  wheel,  as  is 
the  case  with  dishes  and  plates.  The  articles  are  very  slowly  dried 
at  atmospheric  temperature,  and  then  burned  at  a  low  red  heat,  to 
give  them  sufficient  coherence  to  permit  of  glazing. 

The  finely  powdered  glaze  mixture  is  stirred  up  with  water  to 
form  a  cream,  into  which  the  articles  are  dipped  and  at  once  with- 
drawn. A  layer  of  the  glaze  adheres  to  the  surface,  and,  after  dry- 
ing, the  article  is  ready  for  the  second  or  glaze  burning.  In  order 
to  protect  them  from  direct  contact  with  the  fire  in  the  kiln,  they 
are  enclosed  in  fire-clay  boxes,  called  "saggers."  These  are  piled 
in  the  kiln  in  columns  or  "bungs,"  extending  from  the  bottom 
to  the  top.  In  order  to  allow  sufficient  freedom  for  shrinkage,  the 
porcelain  is  supported  on  a  "  cockspur,"  a  small  tripod  of  fire-clay. 
The  contraction  of  porcelain  on  burning  is  nearly  13  per  cent  of  its 
original  volume.  After  burning,  the  ware  is  sorted ;  much  is  lost 
owing  to  warping,  to  bubbles  in  the  glaze,  and  to  discolorations 
resulting  from  smoke  and  from  iron  oxide  in  the  material. 

The  body  of  all  ware  to  be  glazed  is  called  "  biscuit "  after  the 


184  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

first  firing ;  that  of  soft  porcelain  which,  has  been  hard  fired  is  called 
"  Parian."     Both  are  used  for  statuettes,  medallions,  and  reliefs. 

Stoneware,  which  is  also  a  non-porous  body,  is  made  from  re- 
fractory material,  and  burned  at  high  temperatures.  But  the  color 
of  the  resulting  ware  may  range  from  white  and  gray  to  yellow  and 
brown.  It  is  not  attacked  by  chemicals,  and  withstands  tempera- 
ture changes  fairly  well.  The  finest  quality  is  the  well-known 
"  Wedgwood "  ware,  which  comes  in  various  colors,  and  is  usually 
not  glazed.  The  gray  stoneware,  decorated  with  blue,  now  so  much 
used  for  drinking-mugs  and  ornamental  vases,  is  also  of  this  group. 
Yellow  and  brown  varieties  are  much  used  for  mineral  water-bottles, 
bombonnes,  condenser  tubes,  and  glazed  pipes  in  chemical  factories. 
The  clays  are  less  pure  than  those  for  porcelain,  and  the  ware  is  burned 
without  saggers,  at  a  very  high  temperature.  A  "  salt  glaze  "  is 
used,  to  form  which  common  salt  is  thrown  into  the  kiln,  and,  vol- 
atilizing, combines  with  the  silicates  of  the  stoneware  to  form 
double  silicates  of  soda  and  alumina  on  the  surface  of  the  ware; 
or  the  articles  are  "  slip  glazed "  by  applying  an  easily  fusible  clay 
as  "  slip,'7  before  firing. 

The  kilns  for  potters'  use  are  of  several  kinds.  The  most  com- 
mon form  is  the  up-draught  kiln,  in  which  the  flame  enters  at  the 
bottom  and  passes  up  between  the  "bungs,"  and  out  at  the  chimney 
above.  A  better  form  is  the  down-draught  kiln,  which  is  usually 
built  in  two  stories.  The  lower  story  is  filled  with  the  ware  to  be 
fired  at  the  highest  temperature,  and  the  upper  with  that  to  be 
burned  at  a  less  heat.  The  flame  from  the  grate  passes  up  through 
flues  in  the  kiln  walls,  and  enters  the  lower  chamber  near  the  top. 
It  then  goes  down  between  the  bungs,  and,  through  openings  in  the 
floor,  into  other  flues  in  the  walls,  around  tfre  upper  chamber,  and 
thence  to  the  chimney.  This  kiln  is  economical  of  fuel,  affords 
very  even  temperature  in  the  lower  chamber,  and  utilizes  the  heat 
which  is  lost  in  the  up-draught  kiln.  A  special  form  of  Hoffmann's 
ring  furnace  (p.  157)  is  also  employed  for  pottery  and  brick  burning. 
In  a  new  form  of  kiln,  the  bungs  are  arranged  on  cars,  which  travel 
slowly  through  a  long  gallery,  towards  the  firing  chamber.  The 
waste  heat  from  the  hot  chamber  enters  the  gallery  at  the  end  next 
the  firing  room,  and,  coming  in  contact  with  the  pottery,  heats  it  to 
a  temperature  corresponding  to  its  distance  from  the  inlet  flue.  The 
cars  move  through  the  furnace  into  a  second  long  gallery,  where  the 
heat  from  the  saggers  warms  the  air  which  is  passing  into  the  fur- 
nace, thus  perfectly  utilizing  the  waste  heat.  The  firing  compart- 


CERAMIC   INDUSTRIES  185 

ment  is  usually  large  enough  to  contain  two  loaded  cars;  and  the 
grate  being  at  one  end  of  the  firing  room,  the  pottery  in  each  car 
gets  a  preliminary  firing  before  it  reaches  the  hottest  part  of  the 
kiln.  As  soon  as  one  car  is  fired,  it  is  pushed  into  the  cooling  gal- 
lery, the  rear  car  is  moved  into  the  hottest  compartment  of  the  kiln, 
and  another  is  introduced  from  the  preliminary  warming  gallery. 
This  furnace  is  very  economical  of  fuel,  gives  an  even  temperature, 
and  the  time  of  firing  being  greatly  reduced,  there  is  less  loss  of 
saggers  and  pottery. 

Porous  ware,  the  second  division  of  ceramics,  is  manufactured 
extensively  in  all  countries.  The  finest  grade  is  "  faience."  This  is 
made  from  a  white  clay,  which  is  washed,  levigated,  and  aged, 
much  as  for  porcelain.  The  better  grades  are  burned  in  saggers  at 
a  high  temperature,  and  glazed  with  a  transparent  lead  glaze  at  a 
much  lower  heat.  Majolica  also  belongs  to  this  group,  being  a 
colored  porous  body,  covered  with  a  non-transparent  glaze. 

Between  faience  and  common  pottery  no  sharp  line  can  be  drawn. 
The  color  ranges  through  cream,  yellow,  brown,  and  red,  and  the 
body  consists  of  more  or  less  fusible  clay,  with  a  still  more  fusible 
lead  glaze,  which  is  often  colored  with  metallic  oxides.  The  clays 
for  common  pottery  are  generally  "  slipped,"  and  strained  through 
fine  sieves  to  remove  stones  and  coarse  grains.  The  articles  are 
fashioned  on  the  potter's  wheel  and  are  air  dried.  They  are  then 
dipped  in  a  glaze  made  of  litharge  and  clay,  shaken  to  a  cream 
with  water.  Or  the  dry  mixture  is  powdered  over  the  surface  from 
a  pepper  box.  Or  they  are  given  a  "  salt "  glaze  as  before  described. 
They  are  burned  without  saggers,  and  at  a  temperature  only  suffi- 
cient to  fuse  the  glaze. 

Tiles  are  a  special  form  of  pottery,  consisting  of  flat,  thin  plates, 
much  used  for  floors,  panels,  and  architectural  purposes.  They  are 
finer  ware  than  common  brick,  and  more  care  is  taken  in  the  prepa- 
ration of  the  body  and  in  the  burning.  There  are  three  classes, 
vitrified,  encaustic,  and  glazed. 

Vitrified  tiles  consist  of  single  pieces,  made  by  one  burning  at  a 
very  high  temperature,  so  that  the  entire  body  of  the  tile  is  semi- 
fused.  They  are  not  glazed,  and  are  a  form  of  stoneware  much 
used  for  pavements  and  floors,  because  of  their  hardness. 

Encaustic  tiles  are  made  from  two  or  more  clays,  generally  of 
different  colors.  A  facing  of  fine  clay  may  be  put  on  a  back  of 
commoner  quality.  The  ornamental  design  is  made  by  inlaying  the 
face  with  other  clays,  which  burn  to  different  colors.  All  the 
materials  must  have  the  same  coefficient  of  expansion,  so  that  no 


186  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

cracks  form  between  the  different  parts  of  the  design.  These  tiles 
are  generally  used  for  ornamental  purposes,  and  are  often  covered 
with  a  transparent  glaze,  necessitating  two  burnings. 

Glazed  tiles  are  made  with  a  body  (which  may  consist  of  more 
than  one  clay)  of  uniform  color,  covered  with  a  transparent  glaze, 
colored  or  not,  according  to  the  effect  desired. 

The  dry  clay,  flint,  felspar,  Cornish  stone,*  "grog,"  and  other 
materials  in  the  mixture  for  the  body  of  the  tile,  are  put  into  a 
revolving  drum  (Alsing  mill),  along  with  a  number  of  round  flint 
stones.  After  five  or  six  hours'  grinding,  the  mixture  is  complete. 
The  dry  powder  is  then  sifted  through  a  fine  sieve.  There  are  two 
methods  of  forming  the  tile,  the  "dust  body"  and  the  "wet  body" 
process.  In  the  dust  body  method  the  sifted  clay  mixture  is  dampened 
by  spreading  on  a  wet  plaster  of  Paris  floor.  It  is  shovelled  over 
and  allowed  to  remain  on  the  floor  until  the  particles  of  clay  will 
just  stick  together  when  pressed  in  the  hand.  It  is  then  filled  into 
a  metallic  mould  which  contains  the  intaglio  for  relief  designs ;  it  is 
then  heavily  pressed  in  a  screw  or  hydraulic  press.  This  compacts 
the  clay,  and  gives  sufficient  coherence,  so  that  the  green  tile  may  be 
removed.  It  is  exceedingly  brittle,  and  must  be  handled  very  care- 
fully. It  is  well  dried  in  a  room  where  there  is  a  good  circulation 
of  air.  To  prevent  discoloration,  tiles  are  burned  in  saggers  in 
which  they  are  loosely  packed  in  quartz  sand  to  prevent  their  twist- 
ing and  bending,  since  they  become  very  soft  at  high  temperatures. 

In  the  wet  body  process  the  slip  is  moulded  in  plaster  of  Paris 
moulds.  After  standing  half  an  hour,  or  more,  until  the  water  has 
all  been  absorbed  by  the  plaster,  the  clay  cast  is  removed,  dried 
slowly,  and  burned  as  in  the  case  of  dust  body  tiles. 

Glazes,  both  for  hollow  ware  of  all  sorts  and  for  tiles,  are  of  three 
kinds,  engobe,  enamel,  and  transparent. 

The  engobe  is  a  fusible  clay,  felspar,  or  alkali,  applied  in  a  very 
thin  coating.  It  forms  a  thin  glaze,  usually  opaque,  which  is  intended 
to  support  a  second  thicker  glaze  or  enamel. 

Enamels  are  usually  transparent  glazes,  holding  in  suspension, 
opaque  substances  such  as  oxide  of  tin.  A  mixture  of  litharge  and 
tin  oxide  ("ashes  of  tin")  is  very  often  used  for  enamel. 

Transparent  glazes  are  practically  lead  or  lime  glass.  This  is 
sometimes,  though  rarely,  used  as  "raw  glaze,"  i.e.  the  materials 
are  ground  fine,  mixed,  and  applied  to  the  ware  as  a  cream  with 

*  Cornish  stone  is  partly  weathered  felspar,  being  thus  a  mixture  of  kaolin, 
felspar,  quartz,  and  mica.  It  is  mined  in  England,  and  much  used  as  a  flux  and 
fusible  ingredient  in  porcelain  and  tiles. 


CERAMIC   INDUSTRIES  187 

water.  This  is  difficult  to  do,  owing  to  the  great  density  of  the 
litharge,  which  settles  out  of  the  cream,  on  standing  even  a  short 
time.  To  avoid  this  separation  and  loss,  and  to  allow  the  use  of  sub- 
stances soluble  in  water,  e.g.  borax,  soda-ash,  or  boric  acid,  the  glaze 
is  generally  "fritted"  or  semi-fused,  before  making  it  into  a  cream 
with  water.  The  powdered  and  thoroughly  mixed  material,  together 
with  coloring  substances  if  desired,  is  heated  in  a  sagger  until  it 
forms  a  coherent  mass,  but  is  not  completely  fused.  The  frit  is  then 
powdered  in  a  ball  mill.  Fritted  glaze  is  much  more  uniform  than 
raw,  and  there  is  no  tendency  to  segregation  of  its  components. 

In  all  kinds  of  glazed  ware,  it  is  very  essential  that  the  glaze 
and  body  shall  have  the  same  coefficient  of  expansion,  or  cracking 
of  the  glaze  is  liable  to  occur.  This  is  called  "crazing,'7  and  is 
caused  by  the  glaze  contracting  too  much  in  cooling ;  the  scaling  off 
of  glaze  and  attached  body  from  high  points  of  the  tile,  called 
"  shivering,"  is  caused  by  insufficient  contraction  of  the  glaze.  To 
prevent  these  defects  the  glaze  or  the  body  is  so  modified  that  the 
coefficients  of  expansion  are  the  same.  The  exact  adjustment  of 
this  factor  is  a  matter  of  experience.  The  usual  methods  employed 
are,  —  to  render  the  body  less  plastic  by  the  addition  of  lean  clay, 
grog,  or  quartz,  thus  increasing  the  silica,  which  increases  the  expan- 
sion of  the  body ;  or  to  modify  the  glaze  by  the  addition  of  silica 
or  boric  acid  for  greater  expansion,  or  of  lime,  lead,  or  alkali,  to 
increase  the  contraction.  Boric  acid,  lead,  and  alkali  make  it  more 
fusible,  and  the  temperature  of  the  intended  burning  must  be  kept 
in  mind  when  adding  these  ingredients.  Boric  acid  and  lead  also 
increase  the  brilliancy  of  the  glaze.  The  addition  of  certain  color- 
ing matter  to  glazes  also  increases  the  tendency  to  craze.  Alumina 
is  essential  in  a  glaze  to  prevent  devitrification  during  the  burning. 

Terra  cotta  has  a  soft  porous  body,  and  is  not  glazed.  Its  color 
depends  on  the  character  of  the  clay.  Generally  a  highly  ferrugi- 
nous clay  is  used,  which  has  a  deep  red  color  when  burned.  It  is 
extensively  employed  for  architectural  effects  and  for  tiles. 

Bricks  are  probably  the  most  important  of  the  porous  ware. 
They  are  made  from  common  clay,  which  usually  contains  consider- 
able impurity,  lime  and  iron  oxide  often  being  present  in  large 
quantities.  The  preparation  of  the  clay  is  a  simpler  process  than 
for  pottery.  After  digging  it  is  usually  weathered  for  several 
months,  and  then  screened,  to  remove  pebbles  of  quartz  or  lime- 
stone.* It  is  then  "  pugged  "  or  "  tempered,"  by  mixing  thoroughly 

*  Limestone  pebbles  are  very  injurious,  since  the  burning  converts  them  into  lumps 
of  lime  within  the  brick,  and  when  the  latter  is  wet  or  exposed  to  weather  the  lime 
is  hydrated,  and,  expanding,  disintegrates  the  brick. 


188  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

with  water  and  the  ingredients  to  make  the  desired  "  body  " ;  in  the 
case  of  a  fat  clay,  these  are  sand,  grog,  or  other  clays.  This  is  done 
in  a  "  pug  mill,"  a  tank  containing  a  very  effective  revolving  stirring 
apparatus,  which  pushes  the  mass  out  at  the  bottom  in  proper  condi- 
tion to  be  used  at  cnce.  The  paste  is  then  moulded  into  bricks,  by 
hand  for  the  finer  sort,  and  by  machinery  for  the  common  grades. 
The  latter  are  apt  to  be  uneven  and  rough.  The  moulded  brick  are 
then  dried  in  the  air,  usually  in  the  yard,  under  a  light  shed.  They 
are  turned  over  frequently  during  the  drying,  which  must  not  be 
too  rapid,  lest  the  bricks  crack. 

The  firing  is  done  in  kilns  which  may  be  built  of  the  air-dried 
brick,  numerous  channels  being  left  for  the  passage  of  flame  and  hot 
gases.  This  mode  of  burning  results  in  several  grades  of  brick, 
owing  to  the  unequal  distribution  of  heat.  Or  closed  kilns,  such  as 
the  Hofmann  ring  furnace  (p.  157),  may  be  used.  This  gives  a  more 
even  product  than  the  open  kiln. 

In  this  country  wood  and  coal  are  used  for  fuel,  but  gas  is  fre- 
quently employed  abroad.  The  temperature  in  the  kiln  for  common 
brick  seldom  goes  higher  than  1000°  C. ;  but  for  hard,  paving  brick 
it  may  be  raised  to  1200°  or  1300°  C.,  producing  incipient  fusing. 
The  heat  also  affects  the  color  of  some  bricks;  high  temperature 
yields  a  dark  red,  gray,  or  bluish  black,  according  to  the  amount  of 
ferroso-ferric  oxide  (Fe304)  formed.  Clays  containing  much  lime 
yield  yellow  or  cream-colored  brick,  if  iron  is  also  present. 

Common  brick  will  fuse  if  exposed  to  high  heat,  and  are  not 
suitable  for  lining  fireplaces,  furnaces,  or  ovens. 

Fire-brick  are  made  from  fire-clay,  with  the  addition  of  a  large 
amount  of  "  grog "  or  silica.  These  bricks  must  resist  great  heat, 
and  not  shrink  nor  warp.  The  clay  is  prepared  similarly  to  that 
for  common  brick,  but  more  care  is  taken  in  the  mixing.  The 
bricks  are  also  heavily  pressed  to  give  them  density.  The  burning 
is  at  the  highest  temperature  possible,  so  that  110  shrinkage  will 
occur  later  when  the  bricks  are  in  use.  They  are  brittle,  and  must 
be  supported  by  a  backing  of  common  hard  brick. 

Fire-brick  are  also  made  of  highly  basic,  or  of  acid  material,  in 
order  to  better  withstand  the  action  of  fluxes. 

REFERENCES 

Handbuch  der  gesammten  Thonwaarenindustrie.     Bruno  Kerl,  Braunschweig, 

1879.     (Schwetsche.) 

Traite  des  Arts  ceramiques  ou  des  Poteries.     Alexandra  Bronginart. 
Lemons  de  ceramique.    A.  Salvetat. 
La  Faience.    Th.  Deck, 


PIGMENTS 


189 


Report  »on  the  clay  deposits  of  Woodbridge,  South  Amboy,  etc.  Public  Docu- 
ments of  New  Jersey. 

A  Practical  Treatise  on  the  Manufacture  of  Bricks.     C.  T.  Davis. 

Pottery  and  Porcelain  of  the  United  States.     E.  A.  Barber. 

Die  Steingut-Fabrikation.     Gustav  Steinbrecht,  Leipzig,  1891.     (Hartleben.) 

Ziegel-Fabrikation  der  Gegenwart.    Herman  Zwick,  Leipzig,  1894.    (Hartleben.) 

Seger's  gesammelte  Schriften.     H.  Hecht  und  E.  Cramer,  Berlin,  1896. 

The  Chemistry  of  Pottery.  Karl  Langenbeck,  Easton,  Perm.,  1895.  (Chemical 
Publishing  Company.) 

PIGMENTS 

Pigments  are  mineral  or  organic  bodies,  usually  insoluble  in 
water,  oils,  and  other  neutral  solvents,  and  are  used  to  impart  color 
to  a  body,  either  by  mechanical  adhesion  to  its  surface  or  by  ad- 
mixture with  its  substance.  In  most  cases  there  is  no  chemical 
combination  between  the  pigment  and  the  body  it  colors. 

Pigments  form  the  basis  of  paint,  which  consists  of  a  mixture  of 
a  pigment  with  some  drying  oil,  or  with  water  containing  gum  or 
size.  It  is  used  for  decorative  and  protective  purposes ;  if  used  for 
outside  work,  the  pigment  should  be  insoluble  in  water. 

The  color  of  a  pigment  depends  upon  the  amount  and  kind  of  light 
which  it  reflects.  It  is  essential  that  the  pigment  be  opaque,  in  order 
that  it  may  have  a  good  "  covering  power  "  or  "  body ;  "  i.e.  it  should 
entirely  conceal  the  surface  to  which  it  is  applied.  Many  pigments 
are  prepared  by  chemical  precipitation,  but  some  of  the  most  impor- 
tant are  not.  The  chief  pigments  are  given  in  the  following  table  :  — 


WHITES. 

White  Lead. 
Lead  Sulphate. 
Lead  Oxychloride. 
White  Zinc. 
Zinc  Sulphide. 
Barytes. 
Gypsum. 
Whiting. 

BLUES. 

Ultramarine. 
Prussian  Blues. 
Smalt. 

Cobalt  Blues. 
Copper  Blues. 
Indigo. 

VIOLET. 

Ultramarine. 


GREENS. 

Ultramarine. 

Brunswick  Green. 

Chrome  Green. 

Guignet's  Green. 

Copper  Greens. 

Copper  and  Arsenic  Greens. 

YELLOWS. 
Chrome  Yellow. 
Yellow  Ochre. 
Cadmium  Yellow. 
Orpiment. 
Litharge. 
Gamboge. 
Indian  Yellow. 

ORANGE. 
Orange  Mineral. 
Chrome  Orange. 
Antimony  Orange. 


REDS. 

Red  Lead. 
Chrome  Red. 
Red  Ochre. 
Venetian  Red. 
Vermilion. 
Realgar. 
Antimony  Red. 
Carmine. 

BROWNS. 

Umbers. 

Vandyke  Brown. 
Sepia. 

BLACKS. 

Lampblack. 
Ivory-black. 
Bone-black. 
Graphite. 


190  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 


WHITE    PIGMENTS 

White  lead  is  the  most  important  of  all  pigments,  and  is  a  very 
old  one,  the  native  carbonate,  cerussite,  having  been  used  by  the 
Romans.  But  as  this  mineral  is  restricted  in  its  distribution  the 
artificial  product  was  in  time  brought  into  use.  The  so-called  Dutch 
process  of  making  white  lead  is  the  oldest  known,  reference  being 
made  to  it  as  far  back  as  1622.  With  a  few  modifications,  it  is  still 
in  use,  and  yields  a  product  which  for  many  purposes  is  preferred 
by  painters  to  the  lead  manufactured  by  the  numerous  newer  pro- 
cesses. It  usually  has  more  covering  power  and  a  better  color. 

White  lead  is  a  basic  lead  carbonate,  and  analyses  of  the  best 
samples  give  as  constitutional  formula  about  2  PbC03,  Pb(OH)2,  in 
which  there  are  two  molecules  of  PbC03  to  one  of  hydroxide.  This 
appears  to  be  the  best  ratio.  But  the  white  lead  of  trade  varies  a 
good  deal,  according  to  the  method  and  conditions  of  making.  In 
some  cases  it  is  nearly  pure  PbC03,  and  in  others  the  proportion  of 
carbonate  to  hydroxide  is  as  high  as  three  to  one,  or  more.  But 
some  hydroxide  is  necessary  in  order  that  the  white  lead  may  have 
a  good  covering  power.  Then,  too,  the  hydroxide  is  supposed  to 
combine  with  the  oil  chemically  to  form  a  "  lead  soap,"  which  per- 
haps dissolves  in  the  excess  of  oil  to  form  a  kind  of  varnish. 

There  are  three  general  methods  employed  in  white  lead  making, 
besides  numerous  patent  processes.  These  are :  — 

The  Dutch,  or  Stack  process. 

The  German,  or  Chamber  process. 

The  French,  or  Thenard's  process. 

The  Dutch  process  consists  in  exposing  sheet  lead  to  the  direct 
action  of  moisture,  acetic  acid  vapors,  and  carbon  dioxide.  The 
corrosion  is  effected  in  earthenware  pots  8  inches  in  depth  by  5 
inches  in  diameter,  glazed  inside,  and  made  in  the  form  of  crucibles, 
each  containing  a  shelf.  On  this  shelf  is  a  spiral  or  "buckle"  of 
thin  sheet  lead,  made  by  rolling  up  a  sheet  of  lead  2  feet  long 
by  4  inches  wide ;  or  cast  buckles  of  various  forms  to  expose  a 
large  surface  to  the  fumes,  may  be  used.  In  the  lower  compart- 
ment is  dilute  acetic  acid,  containing  from  3  to  5  per  cent  C2H402. 
A  large  number  of  these  pots  so  charged  are  packed  in  a  shed  or 
brick  building,  having  an  opening  on  one  side  reaching  from  the 
ground  nearly  to  the  roof.  A  layer  of  ashes  is  spread  over  the 
floor  first,  and  then  a  layer  4  or  5  feet  thick  of  spent  tan  bark  which 
is  moist  and  ready  to  ferment.  This  is  well  packed  down,  and  the 
pots  placed  side  by  side  upon  it  until  the  whole  space  is  filled, 


PIGMENTS  191 

excepting  about  6  inches  next  the  walls,  which  is  solidly  filled  in 
with  the  tan.  More  lead  buckles  or  lead  gratings  are  placed  across 
the  tops  of  the  pots,  so  as  to  form  a  layer  of  metallic  lead  about  4 
inches  deep.  Then  about  6  inches  above  this,  and  supported  by 
timbers  or  blocks,  is  a  board  floor  upon  which  the  next  layer  of  tan, 
about  one  foot  deep,  is  placed,  and  the  pots  upon  it  as  above  described. 
The  doorway  is  boarded  up  as  the  filling  continues,  and  the  "  stack," 
as  the  alternate  layers  of  pots  and  tan  are  called,  is  carried  to  within 
a  few  feet  of  the  top  of  the  shed.  For  a  stack  20  by  12  by  18  feet 
in  size,  40  or  50  tons  of  lead  are  required,  about  3  tons  of  lead 
and  200  gallons  of  acid  being  used  in  each  layer  of  pots.  Very  soon 
after  packing  an  active  fermentation  of  the  tan  sets  in,  the  tempera- 
ture rising  to  about  55°-60°  C.  This  heat  is  sufficient  to  vaporize 
the  acetic  acid  and  water,  and  these  vapors  attack  the  metallic  lead, 
forming  a  basic  lead  acetate.  Great  quantities  of  carbon  dioxide  are 
liberated  during  the  fermentation,  and  this  decomposes  the  lead 
acetate,  forming  basic  lead  carbonate,  or  white  lead.  The  reactions, 
aside  from  those  of  fermentation,  may  be  represented  by  the  follow- 
ing:— 

1)  Pb  4-  2  C2H402  =  H2  -f  Pb(C.,H302)2.     (Normal  lead  acetate.) 

2)  3  Pb(C2H302)2  4-  2  H20  =  2  Pb(C2H302)2,  Pb(OH)2  +  2  C2H402. 

3)  2  Pb(C2H302)2/  Pb(OH)2  +  2  C02  4-  2  H20 

=  2  PbC03,  Pb(OH)2  4-  4  C2H402. 
Some  authorities  consider  the  reactions  to  be  as  follows :  — 

a)   Pb  4-  H20  4-  0  =  Pb(OH)2. 

6)   Pb(OH)2  4-  2  C2H402  =  Pb(C2H302)2  4-  2  H20. 

c)  Pb(C2H302)2  4-  2  Pb(OH)2  =  Pb(C2H302)2, 2  Pb(OH)2.    (Basic  lead 

acetate.) 

d)  3  ;Pb(C2H302)2,  2  Pb(OH)2j  4  4  CO2  = 

3Pb(C2H302)2  +  2  >Pb(OH)2,  2PbC03;  +  4H20. 

Thus  the  acetic  acid,  or  the  neutral  lead  acetate,  is  regenerated, 
and  attacks  more  of  the  metallic  lead,  and  the  process  repeats  itself. 
But  the  action  is  very  slow,  the  time  usually  allowed  for  a  stack  to 
work  being  about  three  months.  If  horse  dung  is  used  instead  of 
the  tan  bark,  as  it  formerly  was,  the  process  is  quicker,  taking  about 
two  months ;  but  the  sulphur  compounds  formed  in  this  fermenta- 
tion darken  the  white  lead  more  or  less. 

Usually  the  metallic  lead  is  nearly  all  corroded  and  converted 
into  white  lead,  but  never  completely,  and  the  product  is  seldom 


192  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

equally  good  in  all  parts  of  the  stack.  When  well  corroded,  the 
buckles  retain  their  shape,  although  they  have  become  rather  more 
bulky  and  of  a  grayish  white  color,  and  have  a  firm,  porcelain-like 
structure.  When  soft  and  powdery,  the  product  is  not  so  satis- 
factory. The  coarse  bits  which  fall  among  the  tan  are  recovered  by 
hand  picking  and  raking,  and  the  finer  particles  by  levigation.  The 
"  corrosions  "  are  then  taken  to  the  grinding  room  and  put  through 
rolls,  which  break  them  up  into  fine  powder  ;  the  uncorroded  lead  is 
simply  rolled  out  into  plates  and  scales,  which  are  retained  on  the 
sieves  when  the  mass  is  screened.  The  white  lead  only  passes 
through,  and  is  reduced  to  a  fine  powder  by  wet  grinding  in  an 
edgestone  or  horizontal  mill,  and  then  levigated.  The  coarser  par- 
ticles from  the  first  settling  tanks  are  returned  to  the  mills  and 
reground.  The  supernatant  water  is  drawn  off  from  the  last  settling 
tank,  leaving  a  heavy  white  mud,  which  is  dried  in  unglazed  pots 
or  dishes  by  heating  in  ovens  at  about  80°  C.  During  levigation, 
the  neutral  acetate  mixed  with  the  white  lead  is  dissolved  out. 
The  water  is  used  again  and  again,  until  it  becomes  saturated  with 
lead  salts,  which  are  precipitated  by  adding  soda-ash,  or  by  carbon 
dioxide. 

The  white  lead  comes  in  trade  either  dry  or  mixed  with  about  9 
per  cent  of  raw  linseed  oil.  Sometimes  it  is  slightly  yellow,  due  to 
stains  from  the  colored  liquids  in  the  tan,  or  to  tarry  matters  in  the 
acetic  acid,  or  to  overheating  in  the  drying.  A  little  indigo  or  Prus- 
sian blue  is  sometimes  added  to  neutralize  this.  One  ton  of  the 
metallic  lead  usually  yields  about  1^  tons  of  the  white  lead.  But 
the  process  is  always  somewhat  uncertain  both  as  to  quantity  and 
quality  of  the  product.  Sometimes  very  little  corrosion  takes  place, 
and  this  may  also  vary  in  different  parts  of  the  stack.  The  process 
is  slow,  a  large  plant  is  required,  and  the  capital  invested  lies  idle ; 
hence  the  price  of  white  lead  is  somewhat  higher  than  the  simplicity 
of  the  method  would  at  first  glance  appear  to  warrant. 

To  obtain  good  results  by  the  Dutch  method  the  lead  must  be 
very  pure.  If  any  silver,  copper,  or  iron  is  present,  the  color  of  the 
white  lead  will  be  damaged.  Antimony,  arsenic,  and  zinc  are  said  to 
retard  the  conversion  very  much. 

The  German,  or  chamber,  process  is  an  artificial  method  of  pro- 
ducing about  the  same  conditions  as  prevail  inside  the  stack  in  the 
Dutch  method.  The  reactions  are  the  same.  Lead  plates  are  hung 
or  arranged  on  shelves  in  a  closed  chamber,  provided  with  a  door  and 
window  for  filling  and  for  watching  the  process.  Dishes  of  acetic 
acid  are  placed  on  the  floor,  or  acetic  acid  vapor  is  introduced  from 


PIGMENTS 


193 


stills  outside,  the  room  is  heated  by  steam  to  about  38°  C.,  and  carbon 
dioxide  is  introduced.  This  is  much  more  rapid  than  the  Dutch 
method,  usually  requiring  about  five  weeks,  but  the  quality  of  the 
product  is  not  so  satisfactory.  There  are  difficulties  to  contend  with 
in  the  rate  of  flow  of  the  acid  vapors,  steam,  and  carbon  dioxide,  and 
in  the  regulation  of  the  temperature.  Too  much  acetic  acid  vapor 
causes  loss  of  lead  as  neutral  acetate;  too  much  carbon  dioxide  pre- 
cipitates normal  lead  carbonate;  too  little  acetic  acid  or  too  high 
a  temperature,  with  excess  of  water  vapor,  may  form  lead  oxide, 
which,  being  yellow,  injures  the  product.  Many  modifications  of 
this  process  have  been  invented,  and  some  of  them  are  worked  more 
or  less  successfully.  In  one  form,  the  chamber  is  fitted  with  tracks, 
on  which  cars  are  run,  carrying  the  sheet  lead  in  frames.  A  car 
can  be  run  out,  and  another  introduced,  without  much  loss  of  time 
or  cooling  of  the  chamber. 

The  white  lead  made  by  this  method  is  ground  and  levigated  as 
already  described. 

The  French  process,  or  Thenard's  method,  depends  on  precipitation 
cf  a  basic  lead  carbonate  from  a  solution  of  a  basic  salt  by  means  of 
carbon  dioxide.  The  solution  generally  used  is  a  basic  lead  acetate, 
prepared  by  boiling  litharge  with  neutral  acetate.  The  reactions 
are:  — 

1)  2  PbO  +  Pb(C2H302)2  +  2  H20  =  Pb(C2H302)2,  2  Pb(OH)2. 

2)  3  { Pb(C2H302)2  -  2  Pb(OH)2 j  +  4  C02  = 

3  Pb(C2H302)2  +  252  PbC03,  Pb(OH)2j  +  4  H20. 


FIG.  65. 

The  reactions  are  carried  out  in  the  apparatus  shown  in  Pig. 
65.*  The  litharge  is  mixed  with  the  solution  of  neutral  lead  acetate 
in  the  tank  (A),  which  is  heated  by  a  steam  pipe.  When  saturated, 

*  After  Hurst,  Painter's  Colours,  Oils  and  Varnishes. 
o 


194  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

the  mixture  is  run  into  the  settling  tank  (  B),  where  the  undissolved 
litharge  deposits.  The  clear  solution  of  basic  lead  acetate  is  then 
run  into  the  precipitating  vessel  (C),  where  it  is  treated  with  carbon 
dioxide,  introduced  through  the  pipes  (D,  D).  The  basic  lead  car- 
bonate falls  as  a  heavy  white  precipitate,  while  a  solution  of  neutral 
lead  acetate  remains.  After  settling,  the  solution  is  drawn  into  the 
tank  (E),  from  which  it  is  pumped  back  into  (A),  where,  after  add- 
ing a  small  amount  of  acetic  acid,  it  is  used  again.  The  white  lead 
is  collected  in  (F),  from  which  it  is  taken  to  be  filtered  and  washed. 
The  carbon  dioxide  used  must  be  pure  and  concentrated,  and  is 
made  by  heating  calcium  carbonate  with  coke,  in  a  special  furnace 
(G).  The  gas  is  passed  through  water  in  (H)  to  remove  impurities, 
and  then  goes  to  the  precipitating  vessel. 

The  precipitation  requires  from  10  to  14  hours  or  more,  vary- 
ing, as  does  also  the  quality  of  the  product,  with  the  quantity  and 
strength  of  the  solution  of  basic  acetate.  The  white  lead  separates 
in  a  granular  or  crystalline  form,  and  is  washed,  ground,  and  dried, 
as  in  the  methods  already  described.  It  has  less  covering  power 
than  the  amorphous  powder  produced  by  the  Dutch  method,  since 
the  minute  precipitated  crystals  are  very  difficult  to  pulverize,  and 
are  less  opaque. 

Milner's  process,  one  of  the  several  patented  modifications  of  this 
method,  consists  in  forming  a  basic  lead  chloride  by  mixing  litharge 
in  a  solution  of  common  salt,  and  agitating  for  4  or  5  hours.  The 
reaction  proceeds  at  the  ordinary  temperature,  and  produces  a  thick 
white  paste,  which,  together  with  the  caustic  soda  formed,  is  then 
decomposed  with  carbon  dioxide  in  a  tank  provided  with  stirring 
paddles.  The  resulting  products  are  white  lead  and  common  salt. 
The  mixture  is  tested  from  time  to  time,  and  when  no  longer  alka- 
line the  reaction  is  ended. 

The  reactions  are  :  — 

1)  4  PbO  +  2  NaCl  +  5  H20  =  PbCl2,  3  PbO  -  4  H20  +  2  NaOH. 

2)  3  JPbCl2,  3  PbO  •  4  H2OJ  +  6  NaOH  +  8  C02 

=  4  {2  PbCOg,  Pb(OH)2£  +  6  NaCl  +  11  H20. 

By  the  Kremnitz  process,  so  called  from  the  locality  where  it  is 
employed,  a  thick  paste  is  made  of  litharge  and  acetic  acid  or  lead 
acetate  solution.  This  is  put  into  chambers  filled  with  carbon  diox- 
ide, and  stirred  and  raked  over  until,  having  absorbed  sufficient  car- 
bon dioxide  to  form  the  basic  carbonate,  it  has  become  white.  The 
process  must  be  stopped  at  the  right  point,  or  too  much  normal  car- 
bonate is  formed,  and  the  product  injured. 


PIGMENTS  195 

A  number  of  patents  have  been  issued  for  methods  depending 
upon  the  precipitation  of  basic  lead  solutions  with  sodium  carbonate, 
but  these  all  have  the  disadvantage  of  forming  a  crystalline  product. 

Electrolytic  processes  have  attracted  some  attention  recently. 
One  of  these  is  a  modification  of  the  chamber  method.  The  lead 
is  placed  on  shelves,  covered  with  carbon,  or  pure  tin  plates,  through 
which  an  electric  current  is  passed.  The  lead  is  thus  charged,  and, 
it  is  claimed,  is  consequently  more  rapidly  converted  by  the  carbon 
dioxide  and  acetic  acid  vapors,  while  the  product  is  granular,  instead 
of  crystalline. 

A  new  electrolytic  process  *  consists  in  decomposing  a  solution 
of  sodium  nitrate  in  a  wooden  cell,  provided  with  a  porous  dia- 
phragm. The  anode  is  made  of  metallic  lead,  and  the  cathode  of 
copper.  Nitric  acid  is  set  free  at  the  anode  and  dissolves  the  lead, 
forming  a  solution  of  lead  nitrate.  At  the  cathode,  metallic  sodium 
is  liberated,  which  decomposes  the  water,  forming  caustic  soda. 
Then  the  lead  nitrate  and  caustic  soda  solutions  are  allowed  to  react 
on  each  other,  precipitating  lead  hydroxide,  which  is  digested  with 
a  solution  of  sodium  bicarbonate,  to  form  neutral  lead  carbonate. 
At  the  same  time  that  the  lead  nitrate  is  decomposed  by  the  caustic 
soda,  the  sodium  nitrate  is  regenerated  and  returned  to  the  process. 
The  caustic  soda  solution  formed  in  the  last  reaction  is  used  to 
make  more  sodium  bicarbonate  by  the  addition  of  carbon  dioxide. 
The  lead  carbonate  formed  in  this  way  is  claimed  to  be  non-crystal- 
line, and  to  have  as  much  covering  power  as  the  basic  carbonate  or 
common  white  lead. 

The  reactions  are  as  follows  :  — 

_  I 

1)  NaN03  +  H20  =  NaOH  -f  HN03. 

2)  2  HN03  +  Pb  =  Pb(N03)2  +  H2. 

3)  Pb(N03)2  -f  2  NaOH  =  Pb(OH)2  -f-  2  NaNO3. 

4)  Pb(OH),  +  NaHC03  =  PbC03  +  KaOH  +  H20. 

Keactions  (1)  and  (2)  are  doubtful,  and  it  is  more  probable  that 
the  following  occurs  :  — 


2  NaN03  +  2  H,0  +  Pb  =  (2  NaOH  +  H2)  -f 

Hydrogen  is  liberated  at  the  cathode. 

The  process  is  claimed  to  be  rapid,  requiring  only  a  small  plant 
for  considerable  output  ;  and  it  yields  a  good  paint  with  very  little 
labor. 

Owing  to  the  high  price  of  white  lead,  it  is  frequently  adulterated 
*  J.  Amer.  Chem.  Society,  1895,  p.  835.—  R.  P.  Williams. 


196  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

with  barytes  (BaS04),  lead  sulphate,  lead  carbonate,  or  calcium  car- 
bonate. Barytes  is  the  most  common  adulterant,  being  cheap  and 
heavy.  A  pure  white  lead  should  dissolve  in  dilute  C.P.  nitric  acid, 
without  leaving  a  residue.  (Common  nitric  acid  will  not  yield  a 
perfect  solution,  as  it  contains  sulphuric  acid.) 

White  lead  is  very  heavy,  having  a  specific  gravity  of  6.47.  A 
cubic  foot  of  the  dry  powder  weighs  about  185  pounds.  It  has 
great  value  as  a  pigment,  owing  to  its  covering  power,  its  perma- 
nency, and  the  readiness  with  which  it  mixes  with  other  pigments. 
But  it  turns  dark  on  contact  with  hydrogen  sulphide,  or  if  mixed 
with  pigments  containing  sulphur,  such  as  ultramarine,  cadmium 
yellow  (CdS),  or  vermilion  (HgS).  It  is  not  suitable  for  painting 
the  interiors  of  houses  where  gas  or  coal  is  burned.  It  is  nearly 
insoluble  in  water,  but,  if  taken  into  the  system,  will  in  time  pro- 
duce very  dangerous  poisoning;  and  too  much  care  cannot  be  taken 
in  the  manufacture  to  prevent  the  fine  dust  from  flying  about. 
Sponges  are  worn  over  the  mouth  by  the  workmen,  especially  in  the 
grinding  room.  Sometimes  they  drink  water  acidulated  with  sul- 
phuric acid,  as  a  preventive  and  antidote. 

Owing  to  the  cost  and  poisonous  character  of  white  lead,  substi- 
tutes are  used  to  some  extent.  These  are  lead  sulphate,  sulphite, 
and  oxychloride.  Lead  sulphate  is  the  base  of  "sublimed  white 
lead,"  the  chief  white  lead  substitute.  By  heating  galena  and  coke 
in  a  blast  of  hot  air,  part  of  the  lead  is  reduced  to  the  metallic  state, 
and  part  converted  to  sulphate  and  oxide,  which,  together  with  some 
metallic  lead,  sublime  as  "lead  fume."  This  is  collected  in  cham- 
bers and  subjected  to  a  second  heating  in  a  blast  of  hot  air,  which 
finishes  the  conversion  to  sulphate.  The  zinc  present  in  the  galena 
also  passes  off  with  the  fume,  and  is  converted  to  zinc  white  by  the 
hot  air  blast.  The  color  of  the  sublimed  white  lead  is  sometimes 
improved  by  treating  with  sulphuric  acid.  It  has  good  covering 
power  and  color,  and  is  not  readily  affected  by  hydrogen  sulphide. 
It  mixes  well  with  other  pigments  containing  sulphur,  and  is  non- 
poisonous. 

Lead  sulphite  is  made  by  precipitating  a  basic  acetate  solution 
with  sulphur  dioxide  gas,  or  by  subliming  mixed  lead  and  zinc  ores 
with  carbon,  with  a  limited  supply  of  hot  air. 

Pattinson's  white  lead  is  an  oxychloride  of  lead  (PbClOH), 
made  by  precipitating  a  hot  solution  of  lead  chloride  with  one-half 
the  quantity  of  milk  of  lime  necessary  for  its  complete  decomposi- 
tion. The  pigment  has  good  body  and  color,  but  is  not  now  used. 


. 

PIGMENTS  197 

White  zinc,  or  Chinese  white,  is  zinc  oxide  (ZnO).  It  is  made  by 
distilling  metallic  zinc  in  tire-clay  retorts,  and  leading  the  vapors 
into  a  flue  through  which  air  is  drawn.  On  contact  with  the  air, 
the  hofc  vapor  at  once  inflames  and  burns  to  the  oxide,  which  is 
collected  in  a  series  of  settling  chambers.  Instead  of  the  metal, 
calcined  zinc  ores  may  be  mixed  with  carbon  (e.g.  coke),  and  heated 
in  the  retorts,  the  vapors  being  burned  with  air  as  before.  But  ores 
containing  cadmium  cannot  be  used,  because  cadmium  oxide  also 
sublimes,  and  being  brown,  discolors  the  product.  The  oxide  is  also 
formed  by  calcining  zinc  carbonate  or  hydroxide.  The  natural  car- 
bonate, Smithsonite,  is,  however,  seldom  pure  enough,  and  precipi- 
tated carbonate  must  be  used.  This  is  too  expensive  to  compete 
with  the  combustion  process. 

Zinc  white  is  very  permanent,  and  works  well  in  water  and  in 
oil,  of  which  latter  it  requires  a  very  large  amount,  usually  about 
20  per  cent  of  its  weight. 

Zinc  sulphide  is  sometimes  substituted  for  zinc  white.  This  has 
more  body  than  the  oxide.  As  a  rule,  pure  sulphide  is  not  used, 
but  a  mixture  of  sulphide  and  barium  or  strontium  sulphate,  ob- 
tained by  precipitating  a  zinc  sulphate  solution  with  barium  or 
strontium  sulphide.  This  is  calcined  to  convert  part  of  the  sulphide 
to  oxide.  If  the  vapors  of  zinc  and  sulphur  are  brought  together, 
zinc  sulphide  is  formed;  it  is  collected  in  settling  chambers  from 
which  the  air  is  excluded. 

Zinc  sulphide  whites  are  permanent,  have  good  body  and  color, 
and  mix  well  with  oil  and  with  other  pigments,  excepting  those  con- 
taining lead  or  copper. 

Barytes,  or  barium  sulphate,  occurs  native  in  large  quantities. 
The  mineral  is  finely  ground,  treated  with  hydrochloric  acid  or  with 
sulphuric  acid  to  remove  iron,  and  then  levigated.  Precipitated 
barium  sulphate  (blanc  fixe)  is  obtained  as  a  by-product  in  some 
chemical  industries,  and  is  used  to  a  considerable  extent  as  a  filler 
and  pigment.  It  has  more  body  than  barytes. 

Barytes  is  very  heavy,  is  not  affected  by  sulphur  nor  other 
chemicals,  and  may  be  mixed  with  all  pigments.  It  has  little  body, 
and  does  not  work  well  in  oil,  having  a  streaky  appearance  when 
applied,  and  drying  very  slowly.  Owing  to  its  weight,  one  of  its 
chief  uses  is  to  adulterate  white  lead. 

Gypsum,  terra  alba,  or  mineral  white,  is  used  to  some  extent  as  a 
pigment,  especially  for  wall-paper  printing.  The  mineral  is  simply 
ground,  and  treated  with  acid  to  remove  the  iron.  Precipitated  cal- 
cium sulphate  is  a  by-product  of  many  chemical  operations,  and  is 


198  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

largely  used  as  a  filler  in  paper  making,  and  for  weighting  cloth, 
under  the  names  "  Crown  tiller  "  and  "  Pearl  hardening." 

Whiting,  or  Paris  white,  is  calcium  carbonate.  It  is  prepared  by 
grinding  and  levigating  pure  chalk,  which  occurs  in  large  deposits 
in  England,  France,  and  other  countries.  Precipitated  calcium  car- 
bonate is  a  by-product  from  many  chemical  processes.  Whiting  is 
much  used  to  modify  the  shade  of  other  pigments,  and  as  the  basis 
of  whitewash.  When  mixed  with  from  15  to  18  per  cent  of  linseed 
oil,  it  forms  putty. 

Kaolin,  or  China  clay  (p.  180),  is  sometimes  used  to  modify  the 
shade,  or  to  adulterate  other  pigments.  Its  chief  uses  as  pigment 
are  in  wall-paper  printing,  and  as  filler  in  cloth  and  paper. 


BLUB  PIGMENTS 

Ultramarine  is  the  most  important  blue  pigment.  It  occurs  in 
nature  as  the  mineral  lapis  lazuli,  but  in  such  small  quantities,  and 
the  cost  of  preparation  is  so  great,  that  this  is  of  no  importance 
as  the  source  of  the  pigment. 

Ultramarine  is  probably  a  double  silicate  of  sodium  and  alu- 
minum, together  with  a  sulphide  of  sodium.  But  the  composition 
varies  in  different  samples  having  the  same  physical  properties. 
The  presence  of  sulphides  seems  necessary  for  the  color,  since,  if 
treated  with  acid,  hydrogen  sulphide  is  evolved,  and  the  color  dis- 
appears. Numerous  formulae  have  been  proposed  for  ultramarine. 
Soda  ultramarine,  poor  in  silica,  is  4  (Na2Al2Si208)  -f- N"a;>S4 ;  *  that 
high  in  silica  is  2  (Na2Al2Si3010)  +  Na2S4.* 

Soon  after  the  introduction  of  the  Leblanc  soda  process,  blue 
spots,  resembling  natural  ultramarine  in  color,  were  noticed  in  soda 
furnaces  lined  with  siliceous  material.  This  suggested  the  possi- 
bility of  artificial  ultramarine.  In  1828,  Guimet  in  France  and 
Gmelin  in  Germany  succeeded  in  making  it.  Guimet  kept  his 
method  secret,  but  Gmelin  published  his.  Afterwards,  green,  vio- 
let, and  yellow  ultramarine  were  discovered.  A  white  ultramarine 
is  supposed  to  be  the  basis  of  all  others,  and  to  it  is  assigned  the 
formula:  Na2Al2Si208  4-  NasS.*  Green  ultramarine  is  probably  not 
a  distinct  chemical  compound,  but  a  mixture  of  ultramarines. 

None  of  the  above  ultramarines,  excepting  blue  and  green,  have 
any  commercial  importance. 

The  materials  used  for  making  ultramarines  are  China  clay, 
sodium  carbonate  or  sulphate,  carbon,  sulphur,  and  sometimes  si- 

*  Annalen  der  Chemie,  194,  1-22.  —  R.  Hoffmann. 


PIGMENTS  199 

liceous  matter.  The  purity  of  the  material  is  very  important  as 
affecting  the  shade  of  the  color ;  iron  is  especially  liable  to  make 
it  dull.  There  are  two  methods  of  making  it,  the  sulphate  of  soda, 
or  indirect  method,  and  the  soda-ash,  or  direct  method. 

In  the  sulphate  method,  kaolin,  anhydrous  sodium  sulphate,  and 
charcoal,  or  pure  coal,  are  powdered  and  thoroughly  mixed.  The 
carbon  is  necessary  to  reduce  the  sulphate  to  sulphide.  Some- 
times rosin  is  used  as  a  reducing  substance.  The  kaolin  should 
contain  2  Si02  to  1  A1203,  and  be  as  finely  powdered  as  possible. 
The  mixture  is  packed  in  crucibles  *  having  tight  fitting  covers,  and 
is  heated  at  a  bright  red  heat  for  about  8  hours.  The  furnace  is 
allowed  to  cool  very  slowly,  care  being  taken  that  no  air  has  access 
to  the  contents  of  the  crucibles.  When  cold,  the  mass  is  dull  green 
and  porous,  and  when  ground  and  washed  constitutes  the  ultrama- 
rine green  of  commerce.  It  is  obtained  by  this  process  only. 

To  make  the  blue  ultramarine,  the  green  powder  is  subjected  to  a 
"  coloring  "  process.  It  is  spread  in  shallow  trays  in  layers  about 
1  inch  deep,  and  sprinkled  with  powdered  sulphur.  On  heating,  the 
sulphur  ignites,  and  is  allowed  to  burn  itself  out  with  access  of  air. 
Sometimes  muffles  are  used,  the  sulphur  being  added  in  small  quan- 
tities at  a  time,  and  the  charge  stirred  with  mechanical  stirrers  dur- 
ing heating.  A  part  of  the  sodium  sulphide  is  probably  changed  to 
the  sulphate  or  other  soluble  salts,  and  the  crude  blue  results.  It 
is  powdered  and  washed  to  remove  soluble  salts  (]S"a2S04,  Na2S03), 
and  sometimes  boiled  with  a  sodium  sulphide  solution  to  remove 
any  free  sulphur,  which  is  injurious  to  the  copper  print  rolls  in  cal- 
ico printing.  It  is  then  ground  and  levigated,  the  different  grades 
being  used  for  different  purposes.  The  shade  is  usually  modified  to 
match  certain  standards,  by  blending  several  lots  of  colors. 

The  soda-ash,  or  direst  method,  yields  blue  ultramarine  at  one 
heating,  which  may  be  done  in  muffles  or  in  crucibles.  The  usual 
charge  is  about  2^-  tons,  and  consists  of  soda-ash,  kaolin,  charcoal, 
and  sulphur,  ground  fine  and  packed  firmly  on  the  floor  of  the  muf- 
fle, forming  a  layer  about  14  inches  thick.  A  layer  of  tiles,  luted 
together  with  clay,  is  placed  on  top  of  the  charge,  and  the  front  of 
the  furnace  is  bricked  up,  a  loose  brick  being  left  so  that  samples 
may  be  taken  out  to  determine  the  time  of  heating.  The  process  is 
very  slow,  requiring  3  or  4  weeks,  of  which  10  or  12  days  are  required 
for  the  slow  cooling  of  the  muffle ;  during  all  this  time  great  care  is 

*  In  modern  plants,  muffle  furnaces  are  replacing  the  crucibles  for  making  the 
green  ultramarine.  But  these  must  be  built  very  carefully  to  exclude  the  air;  then 
they  need  much  time  for  cooling,  usually  requiring  10  days  or  more. 


200  OUTLINES  OF   INDUSTRIAL   CHEMISTRY 

necessary  to  exclude  the  air.  The  mass  forms  two  layers,  one  bright 
blue,  and  the  bottom  greenish  blue.  These  are  separated,  washed 
and  levigated.  By  using  large  crucibles  instead  of  the  muffle,  the 
time  of  heating  is  reduced  somewhat,  but  the  breakage  and  extra 
labor  more  than  offset  the  gain. 

To  make  an  ultramarine  which  is  less  sensitive  to  acids,  and 
which  will  withstand  the  alum  used  in  paper  making,  a  high  per- 
centage of  silica  in  the  pigment  is  necessary.  For  such  a  product, 
it  is  customary  to  use  the  soda  process,  and  to  add  powdered  quartz, 
sand,  or  diatom aceous  earth  to  the  charge. 

The  first  heating  is  very  important  in  all  processes  of  making 
ultramarine  blue ;  about  700°  C.  is  the  proper  temperature.  If  over- 
heated, the  mass  may  fuse.  Exclusion  of  air  is  necessary  to  prevent 
oxidation  and  loss  of  sulphur,  which  causes  the  product  to  turn  dull 
green,  brown,  or  gray. 

Ultramarine  blue  is  much  used  in  wall-paper  and  calico  printing ; 
for  neutralizing  the  yellow  color  in  paper  pulp,  crystallized  sugar, 
and  cotton  and  linen  goods ;  for  laundry  blue  ;  for  paint;  for  printers' 
ink ;  and  for  coloring  mottled  soaps.  It  is  a  very  fast  color  to  light, 
soap,  and  alkalies,  but  is  quickly  destroyed  by  even  weak  acids. 

Ultramarine  violet  is  made  by  heating  the  blue,  rich  in  silica, 
to  175°  C.,  in  an  atmosphere  of  chlorine  and  steam.  Some  of  the 
sodium  is  thus  converted  to  salt,  and  removed  by  washing.  The 
violet  may  also  be  formed  by  heating  the  blue  to  about  200°  C.,  with 
2  or  3  per  cent  ammonium  chloride,  in  the  presence  of  air.  It  is 
not  much  used,  as  it  has  little  tinctorial  power. 

Ultramarine  red  is  made  by  heating  the  blue  to  not  over  145°  C., 
in  an  atmosphere  of  dry  hydrochloric  acid  gas,  or  in  the  vapors 
of  nitric  acid.  It  is  of  but  little  importance. 

Prussian  blue,  or  Berlin  blue,  is  the  ferrocyanide  of  iron  (ferric- 
ferrocyanide),  Fe45Fe(CN)6(3.  To  make  it,  a  dilute  solution  of  cop- 
peras (FeS04  •  7  H20),  acidified  with  sulphuric  acid,  is  precipitated 
with  potassium  ferrocyanide  solution.  After  decanting  the  liquor 
the  white  precipitate  of  ferrous-ferrocyanide  is  oxidized  with  nitric 
acid,  or  with  bleaching  powder  and  hydrochloric  acid.  Exposure  to 
the  air  also  causes  oxidation,  but  the  color  thus  obtained  is  not  so 
good. 

Chinese  blue  is  a  very  pure  and  carefully  prepared  Prussian  blue. 
In  order  to  lighten  the  shade,  and  to  make  the  pigment  easier  to 
grind,  a  certain  amount  of  alum  is  added  to  the  copperas  solution 
before  precipitating. 


PIGMENTS  201 

A  blue  which  is  soluble  in  water  results  if  the  iron  solution  is 
poured  into  the  ferrocyanide  solution  in  a  slow  stream,  or  if  Prus- 
sian blue  is  boiled  in  a  ferrocyanide  solution.  In  both  cases,  the 
ferrocyanide  must  be  in  excess. 

Prussian  blue  is  not  affected  by  acids,  and  mixes  well  with  oil, 
but  fades  a  little  on  exposure  to  the  light.  The  color  is  destroyed 
by  alkalies,  and  consequently  it  cannot  be  mixed  with  any  sub- 
stance having  an  alkaline  reaction.  It  has  great  tinctorial  power, 
but  is  transparent,  and  lacks  body.  It  is  dissolved  by  oxalic  acid, 
yielding  a  blue  solution,  formerly  much  used  for  blue  ink. 

TurnbulTs  blue,  a  deep  reddish  blue  precipitate,  is  obtained  by 
precipitating  a  ferrous  salt  with  potassium  ferricyanide,  [K3Fe(C]SI")6], 
instead  of  the  ferrocyanide.  This  is  similar  to  Prussian  blue. 

Smalt  is  a  potash-cobalt  glass,  made  by  fusing  pure  sand  and 
potash  with  cobalt  oxide  (Co203),  in  a  furnace  similar  to  a  glass  fur- 
nace. The  crude  cobalt  oxide,  called  "  zaffre,"  is  made  by  carefully 
roasting  smaltite  (CoAs2),  cobaltite  (CoAsS),  or  cobalt-nickel  py- 
rites [(CoM)2S3].  The  ore  is  carefully  sorted  by  hand,  and  iron 
pyrites  and  other  impurities  removed ;  then  it  is  ground  and  some- 
times levigated,  and  roasted  in  a  reverberatory  furnace.  A  large 
part  of  the  arsenic  and  sulphur  passes  off  as  oxides.  The  arsenic 
trioxide  (As203)  is  condensed  in  long  flues  or  chambers,  while  the 
sulphur  dioxide  escapes  to  the  chimney.  A  small  amount  of  the 
sulphur  and  arsenic  is  left  in  the  zaffre  to  combine  during  the  fu- 
sion, with  the  iron,  copper,  nickel,  and  other  injurious  metals, 
forming  a  speiss,  which,  being  heavier  than  the  glass,  settles  to  the 
bottom  of  the  pot.  The  blue  glass  is  refined  (p.  172)  until  all  the 
impurities  have  settled,  and  is  then  ladled  out  into  water.  This  granu- 
lates it,  and  the  sand  so  formed  is  ground  under  edge-runners  and 
levigated.  The  medium  fine  deposit  is  the  best  grade,  the  finest  being 
too  light-colored.  The  coarse  and  the  very  fine  are  usually  remelted. 

Smalt  is  a  very  permanent  color,  fast  to  light,  and  not  affected  by 
acids  nor  alkalies.  But  it  does  not  work  well  as  a  paint  either  in 
oil  or  in  water,  and  is  expensive;  hence  it  is  now  largely  replaced 
by  ultramarine. 

Imitation  smalt  is  sometimes  made  of  sand,  colored  with  ultra- 
marine. A  simple  test  with  acid  detects  this  at  once.  Prussian 
blue  is  shown  by  treating  with  alkali. 

The  composition  of  commercial  smalt  varies  much ;  it  may  con- 
tain from  2  to  16  per  cent  of  cobaltous  oxide  (CoO),  but  it  is  often 
difficult  to  get  a  good  test  for  the  cobalt. 


202  OUTLINES  OF   INDUSTRIAL   CHEMISTRY 

Cobalt  blue  is  made  as  follows:  alumina  is  heated  to  a  red  heat 
in  a  crucible  with  basic  cobalt  phosphate,  made  by  adding  sodium 
phosphate  to  a  cobalt  nitrate  solution.  Alum  and  sodium  carbonate 
solutions  are  mixed,  and  aluminum  hydroxide  precipitated.  These 
two  products  are  thoroughly  washed,  and  one  part  cobalt  phosphate 
is  mixed  with  8  parts  aluminum  hydroxide,  and  the  mixture  heated 
to  a  red  heat  for  three-quarters  of  an  hour,  or  until  the  blue  color 
develops.  The  pigment  is  then  ground  wet,  washed,  and  dried. 
This  yields  a  good  oil  color. 

Copper  blues  are  not  very  important.  Mountain  blue  is  the 
ground  mineral  azurite,  a  hydrated  copper  carbonate  (2  CuC03, 
Cu(OH)2). 

Bremen  blue  is  a  copper  hydroxide  containing  some  copper  car- 
bonate and  oxychloride.  A  mixture  of  common  salt,  copper  sul- 
phate, and  metallic  copper  in  small  pieces  is  kept  in  tubs  for  several 
weeks,  being  well  stirred  frequently.  A  paste  of  green  oxychloride 
is  formed,  which  is  washed  free  from  all  soluble  salts.  A  small 
quantity  of  hydrochloric  acid  is  then  added,  and  left  for  several 
hours.  Finally,  a  solution  of  caustic  soda  is  added,  and  thoroughly 
mixed  until  the  paste  acquires  a  blue  color.  After  washing  well 
and  drying,  it  is  ready  for  use. 

The  copper  blues  are  altered  somewhat  by  exposure  to  the 
weather.  They  are  readily  darkened  by  hydrogen  sulphide  or  sul- 
phur fumes,  so  cannot  be  mixed  with  pigments  containing  sulphur. 
They  dissolve  in  acids  and  in  ammonia,  and  become  black  when 
heated,  owing  to  the  formation  of  cupric  oxide  (CuO).  They  are 
opaque  in  water,  but  become  slightly  transparent  in  oil  and  lose 
body.  They  are  at  best  a  greenish  blue. 

Indigo  is  an  organic  substance  (p.  466)  somewhat  used  as  a  pig- 
ment in  calico  printing. 

GREEN   PIGMENTS 

Ultramarine  green  is  not  very  largely  used  as  a  pigment.  Its 
preparation  is  described  on  p.  199. 

True  Brunswick  green  is  the  oxychloride  of  copper,  made  by 
allowing  metallic  copper  to  stand  for  a  number  of  weeks  in  a  solu- 
tion of  common  salt  which  contains  sulphates.  The  insoluble  pig- 
ment is  washed  through  a  sieve  to  remove  copper  chips,  and  then 
dried  at  a  low  temperature  to  prevent  decomposition.  It  is  a  good 


PIGMENTS  203 

pigment,  working  well  with  oil,  and  having  a  fair  coloring  power ; 
but  the  color  is  rather  pale. 

The  pigment  now  sold  under  the  name  of  Brunswick  green  is 
generally  a  mixture  of  Prussian  blue,  chrome  yellow,  and  barytes, 
the  proportion  of  each  depending  on  the  shade  desired.  These 
greens  are  prepared  by  the  dry  or  the  wet  methods.  In  the  former, 
the  dry  ingredients  are  mixed  in  a  paint-  or  edgestone-mill.  But 
the  shade  is  inferior  to  that  produced  by  the  wet  method.  In 
this,  copperas  (FeS04  •  7  H20),  lead  acetate,  barytes,  and  potassium 
ferrocyanide  and  bichromate  are  used.  The  iron  and  lead  salts  are 
dissolved  separately,  and  mixed  while  stirring  in  the  barytes ;  some 
lead  sulphate  is  thus  precipitated  also.  Then,  while  still  stirring 
actively,  the  mixture  of  potassium  ferrocyanide  and  bichromate  solu- 
tion is  added.  After  a  few  moments  further  stirring,  the  pigment  is 
allowed  to  settle,  and  the  liquor  is  decanted.  Then  the  precipitate 
is  washed  by  decantation,  filtered,  and  dried  carefully.  Or  the  dry 
ingredients  are  finely  powdered  in  an  edgestone-mill,  and  then 
stirred  up  thoroughly  with  water  in  a  tank  until,  on  settling,  the 
liquor  is  nearly  colorless.  The  precipitate  is  washed  as  above 
described. 

These  greens  are  sometimes  sold  under  the  names  Victoria,  Prus- 
sian, or  chrome  green.  They  work  very  well  in  oil,  have  good  cov- 
ering power,  and  are  fairly  permanent ;  but  they  cannot  be  mixed 
with  pigments  containing  sulphur  or  alkaline  substances,  nor  used 
where  exposed  to  hydrogen  sulphide  gas.  Alkalies  act  both  upon 
the  Prussian  blue  and  the  chrome  yellow,  causing  them  to  turn  red 
or  brown.  Sulphur  darkens  the  chrome  yellow. 

Chrome  greens  are  valuable  pigments,  having  a  light  yellowish 
green  color.  The  basis  is  chromic  oxide  (Cr203).  By  precipitat- 
ing a  solution  of  a  chromic  salt  with  soda,  chromium  hydroxide 
[Cr(OH)3]  is  obtained.  This  is  washed,  dried,  and  calcined  at  a 
red  heat,  until  the  water  is  expelled,  and  chromic  oxide  results. 

Gnignet's  green  *  is  a  chrome  green  made  in  the  dry  way.  A 
mixture  of  3  parts  potassium  bichromate  with  8  parts  boric  acid 
is  heated  to  dull  redness  in  a  reverberatory  furnace  for  four  hours. 
The  porous  mass  is  then  washed,  ground,  and  dried.  In  composi- 
tion, this  green  is  a  hydrated  chromic  oxide,  containing  a  very  small 
quantity  of  boric  acid.  A  chromium  borate  is  formed  by  the  calci- 
nation, which  is  decomposed  by  the  water,  forming  hydrated  chro- 

*  Bulletin  de  la  Societe  de  Paris,  1,  9.  Guignet,  —  Fabrication  des  Couleurs, 
149-153. 


204  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

mic  oxide  (Cr203  •  2  H20),  or  Cr20(OH)4,  and  regenerating  boric 
acid. 

Guignet's  green  is  permanent,  mixes  well  with  oil  and  with  all 
other  colors,  and  has  good  covering  power.  It  is  one  of  the  most 
valuable  pigments. 

Chrome  greens,  consisting  of  chromium  phosphate,  are  sometimes 
made  by  boiling  potassium  bichromate  with  sodium  phosphate  arid  a 
reducing  agent.  These  are  not  so  good  as  the  oxides,  and  have  paler 
shades. 

Copper  greens  containing  only  copper  salts  are  of  little  impor- 
tance. Only  two  need  be  considered  here. 

Mountain  green,  malachite,  or  mineral  green  is  a  basic  copper 
carbonate  [CuC03,  Cu(OH)2],  occurring  as  the  mineral  malachite, 
which  is  much  used  for  ornamental  bric-a-brac  and  lapidary  work. 
When  ground  very  fine,  it  is  sometimes  used  as  a  pigment,  and  is 
permanent  in  the  light,  mixes  well  with  oil,  and  has  fair  covering 
power.  It  is  blackened  by  hydrogen  sulphide.  An  inferior  imita- 
tion of  the  natural  product  is  made  by  precipitating  copper  sulphate 
solution  with  sodium  or  potassium  carbonate  containing  a  little  white 
arsenic  (As203). 

Verdigris  is  not  of  constant  composition,  but  is  a  basic  copper 
acetate,  corresponding  nearly  to  the  formula  [2  Cu(C2H302)2  +  CuO]. 
It  is  sometimes  made  by  covering  copper  plates  in  heaps  of  the 
residue  from  wine  presses.  Fermentation  of  the  mass  produces 
acetic  acid,  which,  together  with  the  moisture,  forms  a  layer  of  ver- 
digris on  the  copper.  This  is  scraped  off,  washed,  and  levigated.  A 
better  product  is  obtained  by  wetting  cloths  in  vinegar  or  in  pyro- 
ligneous  acid,  and  spreading  them  between  the  copper  plates.  Ver- 
digris is  not  a  good  pigment,  being  altered  by  moisture  and  light. 

By  dissolving  copper  oxide,  or  carbonate,  in  acetic  acid,  and 
evaporating  the  solution,  a  crystallized  salt  having  the  composition 
Cu(C2H302)2,  Cu(OH)2-  H20,  is  obtained,  which  is  called  "distilled 
verdigris  "  in  trade.  This,  however,  is  not  a  pigment. 

Copper  and  arsenic  greens  surpass  all  others  in  brilliancy  and 
beauty,  but,  being  exceedingly  poisonous,  cannot  be  used  for  many  pur- 
poses. Scheele's  green,  which  is  chiefly  copper  arsenite  (HCuAs03), 
is  made  by  dissolving  arsenious  acid  in  a  hot  solution  of  potassium 
carbonate,  and  pouring  the  liquid  into  a  solution  of  copper  sulphate. 
The  precipitate  is  carefully  washed  and  dried.  It  is  a  grass-green 
pigment,  having  little  coloring  power,  and  now  seldom  used. 


PIGMENTS  205 

Paris,  or  emerald  green  is  an  acetoarsenite  of  copper, 

[Cu(C2H302)2  •  Ci^As20^7 

prepared  by  adding  a  thin  paste  of  verdigris  in  water  to  a  boiling 
solution  of  arsenious  acid  in  water ;  some  acetic  acid  is  then  added, 
and  the  mixture  boiled  until  the  precipitate  is  of  the  desired  shade ; 
or  the  color  will  develop  by  simply  allowing  the  mixture  to  stand 
for  some  days.  By  Galloway's  process,  sufficient  sodium  carbonate 
is  added  to  a  copper  sulphate  solution  to  precipitate  one-fourth  of 
the  copper.  Then  acetic  acid  is  added  until  the  precipitate  is  just 
redissolved,  and  the  liquid  is  heated  to  boiling.  A  hot  solution  of 
sodium  arsenite  (arsenious  acid  dissolved  in  sodium  carbonate)  is 
then  added,  and  the  mixture  well  stirred.  The  green  precipitate  is 
filtered,  washed,  and  dried  at  a  low  temperature.  For  the  finest 
pigment,  the  solutions  should  be  dilute. 

Paris  green  has  a  peculiar  light  green  shade  possessed  by  no 
other  pigment.  It  is  permanent,  works  well  in  oil,  and  has  a  good 
covering  power.  But  owing  to  its  poisonous  character  its  use  as  a 
pigment  is  much  restricted.  Nearly  the  whole  of  the  present  pro- 
duction is  used  to  exterminate  potato  beetles  and  other  insects  inju- 
rious to  vegetation. 

Terra  verde  is  an  earthy  pigment,  containing  ferrous  silicate  as 
its  chief  ingredient.  Green  earths  are  found  in  numerous  places, 
but  the  best  are  from  Cyprus  and  Italy.  They  are  a  dull  pale  green, 
and  are  permanent,  but  have  little  covering  power. 

YELLOW  PIGMENTS 

The  most  important  yellow  pigments  are  chrome  yellows  and 
yellow  ochres ;  others  are  used  but  little. 

Chrome  yellows  have  as  a  basis  the  chromate  of  lead,  zinc,  or 
barium ;  are  all  made  by  precipitation  and  each  has  a  shade  peculiar 
to  itself.  Lead  chromate  is  made  from  the  lead  acetate,  or  nitrate, 
and  potassium  bichromate.  The  reactions  are  as  follows :  — 

a)  2  Pb(C2H302)2+K2Cr207+H,0=  2KC2H302+2C2H402+2  PbCr04. 
6)  2  Pb(N03)2  +  K2O207  +  H20  =  2  KN03  +  2  HN03  +  2  PbCr04. 

In  order  to  modify  the  shade,  lead,  barium,  or  calcium  sulphate  is 
mixed  with  the  chromate  in  the  grinding-mill.  Or  a  portion  of  the 
lead  is  precipitated  as  sulphate  or  carbonate  along  with  the  chro- 
mate j  this  is  done  by  mixing  sodium  carbonate  or  sulphate  with  the 


206  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

potassium  bichromate.  Chrome  yellows  are  called  "pure"  when 
lead  sulphate  has  been  used  to  modify  the  shade. 

The  precipitate  is  well  washed  by  decantation,  and  the  pulp 
freed  from  water  in  the  filter  press,  or  in  a  centrifugal  machine,  or 
by  pressing  in  cloth  bags.  It  should  be  dried  at  a  low  temperature, 
and  well  ground  either  dry  or  in  oil.  For  the  best  color,  the  lead 
nitrate  should  be  used  in  slight  excess.  When  lead  nitrate  is  used 
in  making  the  chromate,  it  is  customary  to  recover  the  potassium 
nitrate  from  the  liquor  and  first  wash-waters,  the  free  nitric  acid 
being  neutralized  with  pearlash  before  evaporating.  The  excess  of 
lead  salt  is  precipitated  from  the  waste  liquors  on  the  addition  of 
.the  pearlash. 

Chrome  yellow  is  sometimes  made  by  digesting  lead  sulphate 
with  a  hot  solution  of  potassium  bichromate  until  the  desired  shade 
is  developed. 

Lead  chromate  is  a  brilliant  yellow,  mixes  well  with  oil,  and  has 
great  covering  power.  It  is  blackened  by  hydrogen  sulphide,  and 
should  not  be  mixed  with  pigments  which  contain  sulphur,  or  are 
strongly  alkaline.  When  treated  with  a  caustic  alkali,  lead  chro- 
mate is  converted  into  a  basic  salt,  having  a  red  or  orange  color. 
These  basic  chromates  are  prepared  for  pigments,  and  sold  under 
the  name  of  chrome  orange  and  chrome  red.  They  are  made  by  boil- 
ing chrome  yellow  with  calcium  or  sodium  hydroxide.  The  follow- 
ing is  the  reaction  involved :  — 

2  PbCr04  +  2  NaOH  =  Na2Cr04  +  PbCr04,  PbO  -  H20. 

Quicklime  gives  a  paler  color  than  caustic  soda.  Chrome  red  is 
also  made  by  digesting  white  lead  with  potassium  bichromate  and 
caustic  soda. 

Zinc  chromate  is  made  from  zinc  sulphate  and  neutral  potassium 
chromate.  Bichromate  cannot  be  used  because  of  the  ready  solubil- 
ity of  the  zinc  chromate  in  free  acids.  But  if  the  solution  is  alka- 
line, zinc  hydroxide  is  precipitated  also,  hence  the  method  needs 
much  care.  Zinc  chromate  is  also  made  by  boiling  zinc  oxide  with 
potassium  bichromate.  The  pigment  has  a  light  lemon  color,  and  is 
permanent.  It  is  not  affected  by  sulphur,  and  can  be  mixed  with 
other  pigments.  It  is  very  soluble  in  mineral  acids,  and  is  decom- 
posed by  caustic  alkalies. 

Barium  chromate  is  much  like  the  zinc  salt,  but  is  a  greenish 
yellow  color.  It  is  made  in  the  same  way  as  is  the  zinc  chromate, 
but  from  barium  chloride.  It  is  not  used  to  any  extent. 


PIGMENTS  207 

Yellow  ochres  and  Siennas  are  natural  mineral  products,  varying 
from  bright  yellow  to  brown.  The  color  is  due  to  hydrated  oxide  of 
iron,  and  in  Sienna  there  is  a  little  manganese  oxide.  The  pigments 
contain  sand  and  clay  in  large  quantities,  and  are  decomposition 
products  from  iron-bearing  minerals.  The  Siennas  are  usually  finer 
grained  and  contain  less  gangue  mineral  than  the  ochres.  They 
occur  in  beds  in  the  earth,  and  the  only  preparation  necessary  is 
grinding  and  levigating.  They  are  very  permanent,  mix  well  with 
oil  and  with  other  pigments,  have  good  covering  power,  and  are 
cheap.  If  ochres  and  Siennas  are  calcined,  the  water  of  hydration 
is  removed  from  the  ferric  hydroxide,  and  the  color  becomes  orange 
or  red.  Burnt  Sienna,  made  by  heating  raw  Sienna  to  a  low  red 
heat,  is  reddish  orange  in  color. 

Cadmium  yellow  is  cadmium  sulphide  (CdS),  and  is  made  by 
precipitating  a  cadmium  solution  with  hydrogen  sulphide.  If  the 
solution  is  strongly  acid,  the  color  becomes  more  nearly  orange. 

It  is  a  brilliant  yellow,  very  permanent,  and  mixing  well  with 
oil  and  with  other  pigments,  excepting  lead  and  copper  compounds. 
It  is  chiefly  used  as  an  artist's  color.  Sometimes  cadmium  yellow  is 
made  by  using  ammonium  sulphides  instead  of  hydrogen  sulphide 
to  precipitate  the  pigment ;  but  in  this  case  free  sulphur  is  present 
in  the  precipitate,  and  causes  changes  in  the  color  when  mixed 
for  use. 

Orpiment  is  arsenic  trisulphide  (As2S3).  It  is  found  native  as  a 
mineral,  which  is  simply  ground  for  pigment.  It  is  also  extensively 
made  by  precipitating  a  dilute  solution  of  arsenious  acid  in  hydro- 
chloric acid  with  hydrogen  sulphide ;  or  by  subliming  a  mixture  of 
arsenious  acid  and  sulphur  from  a  retort.  The  pigment  obtained  by 
either  method  is  finely  ground. 

Orpiment  is  a  very  bright  yellow,  mixes  well  with  oil,  and  has 
good  covering  power ;  but  it  is  not  permanent  on  exposure  to  light, 
and  cannot  be  mixed  with  many  other  colors.  It  is  also  very  poison- 
ous. It  is  sold  under  the  name  of  royal  yellow,  or  king's  yellow. 

Litharge  is  lead  monoxide  (PbO),  and  is  made  by  oxidizing  metal- 
lic lead  at  a  temperature  so  high  that  the  oxide  formed  is  melted. 
This  is  collected  in  pots,  and  cooled  slowly.  Part  of  the  product 
separates  as  a  flaky  mass,  and  the  remainder  forms  a  hard  cake, 
which  is  ground  and  levigated,  and  forms  a  buff-colored  powder. 
It  is  not  so  important  as  a  pigment  as  for  the  preparation  of 


208  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

"boiled  linseed  oil,"  p.  308.  It  is  also  extensively  used  in  mak- 
ing lead  glass  and  pottery  glazes. 

Another  variety  of  lead  monoxide,  having  a  lighter  yellow  shade, 
is  "  massicot,"  which  is  formed  by  oxidizing  lead  at  so  low  a  temper- 
ature that  no  fusion  of  the  product  takes  place.  It  is  chiefly  pre- 
pared for  the  manufacture  of  red  lead  (p.  209). 

Yellow  lead  oxide  is  also  made  by  heating  white  lead. 

Gamboge  is  a  gum-resin  obtained  from  a  tree  (Gardnia  Morella, 
Desr.)  of  Siam.  Incisions  are  made  in  the  bark  of  the  tree,  and  the 
sap  is  collected  in  bamboo  receivers,  in  which  the  yellow  resin  is 
left  on  evaporation.  Gamboge  emulsifies  with  water,  and  is  used  as 
a  water-color  paint.  It  cannot  be  used  as  an  oil  paint  except  when 
mixed  with  alumina. 

Indian  yellow,  or  purree,  is  made  by  heating  the  urine  of  cattle 
that  have  been  fed  with  leaves  of  the  mango  tree,  the  color  being 
produced  by  an  excessive  secretion  of  bile,  which  has  passed  into 
the  urine.  The  pigment  precipitates,  and  is  pressed  and  dried ;  it 
consists  of  salts  of  euxanthic  acid,  an  organic  body.  It  is  a  bright 
yellow,  but  not  permanent  in  the  light,  and  is  very  expensive. 

ORANGE  PIGMENTS 

Orange  mineral  is  lead  tetroxide  (Pb304),  prepared  by  heating 
white  lead  in  the  presence  of  air.  It  is  usually  made  from  the  scum 
which  collects  on  the  surface  of  wash-waters  used  in  levigating 
white  lead. 

2  PbC03,  Pb(OH)2  +  0  =  Pb304  +  2  C02  +  H20. 

In  composition  and  properties  it  is  similar  to  red  lead  (p.  209), 
but  has  a  slightly  lower  specific  gravity  (6.95). 

Chrome  orange  has  been  described  in  connection  with  chrome 
yellow,  p.  206. 

Antimony  orange  is  antimony  trisulphide,  made  by  precipitating 
a  moderately  concentrated  solution  of  antimony  chloride  with  hydro- 
gen sulphide.  The  precipitate  is  washed  in  dilute  hydrochloric 
acid,  and  then  levigated.  It  must  be  dried  at  a  low  temperature. 

It  has  a  bright  orange  color  in  oil  or  water,  is  permanent  and  of 
good  body,  but  is  decomposed  by  alkalies.  It  is  chiefly  used  for 
vulcanizing  rubber,  producing  the  red  "  antimony  rubber "  of  com- 
merce. 


PIGMENTS  209 


RED   PIGMENTS 

Bed  pigments  form  a  numerous  and  important  group,  containing 
some  of  the  brightest  and  most  permanent  colors. 

Red  lead  is  lead  tetroxide  (Pb304),  having  the  same  chemical 
composition  as  orange  mineral  (p.  208),  but  differing  in  its  physical 
properties.  It  is  made  by  the  direct  oxidation  of  metallic  lead. 
The  process  is  carried  on  in  two  stages.  In  the  first  or  "  dressing  " 
operation  the  lead  is  converted  into  massicot  by  heating  with  free 
access  of  air  in  a  reverberatory  furnace  to  a  temperature  just  above 
that  of  melted  lead  (340°  C.).  The  temperature  must  be  very  care- 
fully regulated,  for  if  the  massicot  melts  it  passes  into  ordinary 
litharge,  from  which  red  lead  cannot  be  made.  As  fast  as  a  layer  of 
oxide  forms  it  is  pushed  to  the  back  of  the  hearth  with  a  "  rabble  "  ; 
finally,  the  unoxidized  lead  is  allowed  to  run  off,  and  the  massicot  is 
raked  out  and  cooled.  It  is  pale  yellow,  of  granular  texture,  and 
contains  pellets  of  unoxidized  lead.  It  is  finely  ground  and  levi- 
gated, and  then  transferred  to  the  second  or  "  coloring  process  " ;  it 
is  heated  to  a  dull  red  heat  in  a  muffle  or  reverberatory  furnace  with 
access  of  air.  The  mass  is  stirred  frequently  to  assist  the  absorp- 
tion of  oxygen,  and  to  develop  the  color.  Samples  are  taken  at  inter- 
vals, until  the  desired  shade  is  obtained,  which  usually  takes  from 
40  to  48  hours ;  then  the  furnace  is  allowed  to  cool.  The  product  is 
usually  ground  before  packing  for  market. 

Red  lead  is  somewhat  variable  in  color,  but  is  a  good  pigment  of 
great  covering  power  and  brilliancy.  It  has  a  specific  gravity  of 
8.5.  Chemically,  it  is  regarded  as  a  mixture  of  lead  monoxide  and 
peroxide  (2  PbO  -f  Pb02),  but  commercial  samples  vary  some  from 
this  formula.  When  treated  with  dilute  nitric  acid,  the  monoxide 
dissolves,  leaving  the  peroxide  as  a  brown  powder ;  this  constitutes 
a  test  for  red  lead,  since  no  other  red  pigment  turns  brown  with 
nitric  acid. 

The  chief  use  of  red  lead  is  for  glass  making,  for  which  a  very 
pure  grade  is  necessary.  Owing  to  its  oxidizing  effect  with  linseed 
oil,  it  is  extensively  used,  mixed  with  this  oil,  as  a  lute  in  plumbing 
and  gas  fitting.  It  is  also  valuable  as  a  painter's  color. 

Chrome  red  is  a  basic  lead  chromate  (PbCr04,  PbO  •  H20),  made 
by  boiling  chrome  yellow  with  caustic  soda  or  with  lime,  as  described 
on  p.  206.  It  is  also  made  by  boiling  white  lead  with  a  solution  of 
neutral  potassium  chromate.  When  the  desired  shade  is  developed, 
the  pigment  is  washed,  ground,  and  levigated. 


210  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

It  is  a  fairly  bright  red,  of  good  body,  working  well  in  oil. 
Like  all  lead  pigments,  it  is  darkened  by  sulphur  and  hydrogen  sul- 
phide. It  is  sold  as  Chinese  red,  American  vermilion,  and  Victoria 
red. 

An  imitation  of  chrome  red  is  made  by  coloring  white  lead  with 
some  of  the  coal-tar  dyes,  especially  with  eosins. 

Red  ochre  is  made  by  calcining  ordinary  ochre  at  a  low  red  heat 
until  more  or  less  of  the  water  of  hydration  is  driven  off.  The 
shade  depends  on  the  time  of  heating,  —  the  longer  the  calcination 
the  more  purple  the  product.  Red  ochres  are  essentially  ferric 
oxide  with  alumina,  silica,  and  lime.  The  native  oxides,  hematite 
and  limonite,  are  seldom  used  for  pigment,  being  hard  to  grind. 
But  in  a  few  places  soft  deposits  of  hematite  are  found,  which  yield 
a  pale  red  pigment  without  further  treatment  than  grinding.  These 
ochres  are  sold  as  Indian  red,  light  red,  Venetian  red,  etc. 

Iron  reds  are  now  being  prepared  in  large  quantities,  chiefly  as 
by-products  from  other  manufactures.  These  are  sold  as  rouge, 
colcothar,  Venetian  red,  etc.,  and  all  contain  ferric  oxide  as  the  col- 
oring matter. 

When  fuming  sulphuric  acid  is  made  by  the  dry  distillation  of 
copperas  (p.  60),  a  residue  of  ferric  oxide  remains  in  the  retort. 
This  is  ground,  levigated,  and  sold  as  colcothar.  It  is  nearly  pure 
Fe203. 

In  the  manufacture  of  galvanized  iron  or  tinned  ware,  the  rolled 
sheet  iron  is  dipped  into  a  bath  of  acid  to  dissolve  any  oxide  from 
its  surface  before  putting  it  into  the  bath  of  melted  zinc  or  tin. 
These  acid  "  dipping  liquors "  contain  much  iron,  which  is  precipi- 
tated by  adding  soda-ash  or  lime,  and  used  as  pigment.  If  sulphuric 
acid  is  used  in  the  dipping  liquors,  and  is  neutralized  with  lime,  the 
precipitate  consists  of  ferric  hydroxide,  with  more  or  less  calcium 
sulphate.  By  calcining,  a  light  red  pigment,  called  Venetian  red, 
is  formed. 

Many  metallurgical  operations  yield  liquors  containing  much 
iron,  which  is  precipitated  with  lime,  forming  Venetian  red. 

These  iron  reds  are  very  permanent,  and  valuable  pigments. 
They  work  well  in  oil,  mix  with  all  other  pigments,  have  very 
good  body,  and  are  cheap,  but  the  color  is  not  so  bright  as  in  some 
pigments. 

Vermilion  is  mercuric  sulphide  (HgS).  It  occurs  in  nature  as 
the  mineral  cinnabar,  but  the  pigment  is  now  all  made  artificially. 


PIGMENTS  211 

It  is  one  of  the  brightest  reds,  and  has  been  known  for  a  long  time. 
It  is  made  in  two  ways,  by  the  wet  and  by  the  dry  process.  In 
the  wet  process,  100  parts  of  mercury  are  ground  with  38  parts  of 
flowers  of  sulphur  until  thoroughly  incorporated ;  then  the  mass  is 
digested  at  about  45°  C.,  with  a  solution  of  25  parts  caustic  potash  in 
150  parts  water.  The  mixture  is  stirred  frequently,  and  any  water 
lost  by  evaporation  is  replaced.  After  2  or  3  hours  the  mass  be- 
comes brown,  and  then  gradually  turns  red.  When  the  desired 
color  is  acquired,  which  usually  takes  about  8  hours,  the  pigment  is 
at  once  washed  by  decantation,  since  further  action  of  the  potash 
dulls  the  color.  The  pigment  is  ground,  and  dried  carefully.  The 
temperature  must  be  kept  between  40  and  45°  C.,  for  if  over-heated 
it  becomes  brown.  Solution  of  potassium  or  sodium  polysulphide 
may  be  used  instead  of  the  potash.  The  brilliancy  of  the  color  may 
be  increased  by  treating  with  hydrochloric  or  nitric  acid. 

The  dry  methods  yield  the  best  product.  The  Dutch  process  con- 
sists in  heating  mercury  and  sulphur  together  in  shallow  iron  pans 
until  they  combine  to  form  a  black  mercuric  sulphide  (HgS,  ethiops 
mineral).  This  is  pulverized,  and  introduced  into  earthenware  re- 
torts in  small  amounts  at  a  time.  The  larger  part  of  the  black  sul- 
phide sublimes  into  the  upper  part  of  the  retort  as  a  bright  red 
powder.  This  is  ground,  washed,  treated  with  acid,  and  levigated. 

Chinese  vermilion  is  the  finest  quality,  and  its  manufacture  was 
long  kept  a  secret.  Now  it  is  known  to  be  made  by  a  process  simi- 
lar to  the  Dutch  method,  but  owing  to  the  patience  and  care  exer- 
cised by  the  Chinamen  a  very  fine  product  is  obtained. 

Vermilion  is  a  very  heavy,  opaque,  and  brilliant  pigment.  Owing 
to  its  weight,  it  settles  out  of  the  oil  when  used  for  paint,  causing 
difficulty  in  applying  it  evenly.  It  is  permanent,  and  not  readily 
affected  by  acids  and  alkalies.  When  heated  in  a  closed  tube  it 
turns  black,  and  finally  sublimes  unchanged,  thus  furnishing  a  good 
test  for  its  purity.  It  is  sometimes  adulterated  with  red  lead,  iron 
reds,  or  carmine  lakes,  but  these  leave  a  brown  or  black  residue  when 
heated.  Vermilion  is  very  expensive. 

Vermilionettes  are  brilliant  red  pigments,  produced  by  coloring 
neutral  white  bodies,  such  as  barium  sulphate,  lead  sulphate,  or 
white  lead  with  coal-tar  dyes  of  the  eosin  class.  The  white  base  is 
stirred  up  with  a  solution  of  the  dye,  and  lead  acetate  or  alum  is 
added,  which  precipitates  the  color  upon  the  white  base.  Orange 
mineral  is  sometimes  mixed  with  vermilionettes  to  brighten  the 
color.  These  work  well  in  oil,  have  good  body,  and  are  brilliant, 
but  fade  on  exposure  to  the  light. 


212  OUTLINES  OF  INDUSTRIAL   CHEMISTRY 

Realgar,  the  disulphide  of  arsenic  (As2S2),  occurs  in  nature  in 
small  quantities  as  a  brilliant  red  mineral  which,  when  ground,  fur- 
nishes a  fine  pigment.  But  the  chief  supply  is  obtained  artificially 
by  fusing  together  white  arsenic  (As203)  and  sulphur  in  the  proper 
proportions,  or  by  distilling  arsenical  ores  with  sulphur.  The  crude 
product  is  remelted,  and  arsenic  or  sulphur  added,  as  need  be,  to 
give  the  desired  shade. 

As  a  pigment,  realgar  is  subject  to  the  same  disadvantages  as 
orpiment  (p.  207).  It  is  much  used,  however,  in  preparing  "  Bengal 
lights/'  and  for  unhairing  hides  for  tanning. 

Antimony  red,  or  antimony  vermilion,  is  an  oxysulphide  of 
antimony,  made  by  precipitating  an  antimony  chloride  solution  with 
thiosulphate  of  soda.  On  heating  the  solution  to  55°  C.,  a  red 
precipitate  separates.  This  is  washed  and  dried  at  about  50°  C. 
It  is  also  prepared  by  dissolving  tartar  emetic  in  tartaric  acid  solu- 
tion, mixing  with  sodium  thiosulphate,  and  heating  to  90°  C. 

Antimony  red  is  used  for  oil  and  water  colors,  and  to  some  ex- 
tent in  calico  printing.  It  has  good  body,  and  is  permanent  if  not 
mixed  with  alkalies  or  with  alkaline  vehicles. 


Carmine  pigment  belongs  to  the  class  of  pigments  called  "  lakes," 
which  are  metallic  salts  of  organic  color  acids.  The  coloring  matter 
in  carmine  is  the  organic  substance  carminic  acid  (C17H18010),  ob- 
tained from  the  bodies  of  the  cochineal  insect.  The  lake  is  pre- 
pared by  extracting  the  crushed  insects  with  hot  water,  filtering, 
and  adding  a  solution  of  alum  or  tin  chloride,  and  cream  of  tartar. 
After  standing,  the  pigment  precipitates.  Or  the  lake  may  be  pre- 
cipitated at  once  by  adding  sodium  carbonate  to  the  mixed  solutions. 
The  extraction  is  done  in  tinned  copper  vessels,  and  hard  water  is 
said  to  improve  the  color  of  the  pigment. 

Carmine  is  a  very  bright  scarlet,  the  tin  salt  being  brighter  than 
the  aluminum.  It  works  well  in  oil  and  as  a  water  color,  but  fades 
on  exposure  to  sunlight.  It  is  soluble  in  strong  caustic  alkalies. 

Cochineal  lake,  crimson  lake,  Florentine  lake,  and  others,  are  car- 
mine lakes,  containing  a  larger  proportion  of  alumina  or  metallic 
base  than  does  carmine. 

Madder  lakes  and  Brazil-wood  lakes  are  prepared  by  precipitat- 
ing extracts  of  these  substances  with  alum  and  tin,  by  adding  so- 
dium carbonate.  They  furnish  red  pigments  of  various  shades,  but 
lacking  in  coloring  power. 


PIGMENTS  213 

Yellow  lakes  are  made  from  fustic,  Persian  berries,  or  quercitron 
bark  extracts,  in  the  same  way  as  the  madder  lakes  are  made. 

Many  of  the  coal-tar  dyes  may  be  precipitated  as  lakes,  and  a 
great  number  of  pigments  are  thus  prepared.  But  many  of  them 
are  deficient  in  covering  power,  and  lack  permanency  on  exposure 
to  the  light. 

BROWN   PIGMENTS 

Umbers  are  ochres  containing  more  manganese  than  Sienna  con- 
tains. They  are  complex  mixtures  of  silica,  alumina,  iron,  man- 
ganese, lime,  and  other  matter.  There  are  two  varieties,  raw  and 
burnt.  Eaw  umber  has  received  no  f urthur  treatment  than  grinding 
and  levigating.  Burnt  umber  has  been  calcined  at  a  low,  red  heat, 
whereby  more  or  less  of  the  water  of  hydration  of  the  iron  oxide  has 
been  driven  out,  giving  a  darker  shade  to  the  product.  The  best 
umber  comes  from  Cyprus,  but  many  other  localities  furnish  it  in 
various  shades.  It  is  very  permanent,  has  good  covering  power,  and 
mixes  well  with  all  other  pigments.  It  is  not  affected  by  acids  nor 
alkalies,  and  is  very  cheap. 

Vandyke  browns  are  indefinite  mixtures  of  iron  oxides  and  or- 
ganic matter.  They  are  obtained  from  certain  bog-earth  or  peat 
deposits,  or  from  ochres  containing  bituminous  matter.  They  are 
also  made  artificially  from  charred  organic  substances,  such  as  bark, 
cork  cuttings,  or  bone  dust.  Mixtures  of  lampblack,  yellow  ochre, 
and  iron  oxide  are  also  sold  as  Vandyke  browns.  These  pigments 
are  permanent,  mix  well  with  all  other  colors,  and  have  good  body. 

Sepia  is  an  organic  pigment  obtained  from  the  cuttle-fish  (Sepia 
officincdis),  that  secretes  it  as  a  dark  liquid,  to  be  discharged  in  the 
water  to  hide  his  movements  when  disturbed.  It  is  contained  in  a 
small  sac,  which  is  removed  and  dried.  To  purify  the  pigment,  it 
is  dissolved  in  caustic  soda,  and  the  decanted  solution  is  acidified 
with  hydrochloric  acid.  The  pigment  thus  precipitated  is  washed 
and  dried. 

Sepia  is  a  dark  brown,  fine  grained  pigment,  very  permanent  and 
capable  of  mixing  with  all  other  colors.  It  is  chiefly  used  as  a 
water  color  by  artists. 

BLACK   FIGMENTS 

Black  pigments  nearly  all  contain  carbon  as  the  base.  The  most 
important  is  lampblack,  which  is  the  soot  produced  by  the  incom- 


214  OUTLINES  OF   INDUSTRIAL   CHEMISTRY 

plete  combustion  of  organic  substances,  for  the  most  part,  of  an  oily 
or  resinous  nature.  The  knots  and  other  refuse  from  pitch  pine 
and  hemlock,  the  crude  mineral  oils,  residues  from  petroleum  refin- 
ing, and  the  "  dead  oils  "  from  coal-tar  distillation  furnish  most  of 
the  lampblack.  The  burning  is  conducted  at  so  low  a  temperature, 
and  with  such  a  limited  supply  of  air,  that  only  the  hydrogen  of 
the  hydrocarbons  is  consumed,  the  carbon  depositing  as  soot  in  a 
series  of  chambers,  through  which  the  combustion  products  are  led. 
Some  oil  is  apt  to  distill  into  the  first  chamber,  mixing  with  the 
lampblack,  which  is  then  not  good  for  paint,  as  it  dries  very  slowly  ? 
and  is  dangerous  to  store  on  account  of  its  liability  to  spontaneous 
combustion. 

Sometimes  natural  gas  flame  is  directed  against  cold  iron  plates, 
the  sudden  reduction  of  temperature  causing  a  separation  of  carbon, 
which  deposits  on  the  plates. 

Lampblack  is  a  very  fine  grained  pigment,  permanent,  and  of 
great  covering  power.  It  is  difficult  to  mix  with  oil  or  with  water, 
and  dries  very  slowly.  It  is  largely  used  for  printing-ink. 

Ivory-black  is  made  by  heating  the  refuse  from  ivory  working 
in  closed  retorts  until  all  organic  constituents  are  decomposed.  The 
retorts  must  not  be  opened  until  quite  cold.  The  charred  mass  is 
ground  very  fine,  and  yields  the  finest  quality  of  black  pigment.  It 
is  an  intense  black,  but  since  it  acts  like  bone-char  on  organic  coloring 
matter,  it  cannot  be  mixed  with  most  pigments  of  an  organic  nature. 

Bone-black  is  an  inferior  black,  made  from  bones  charred  in  a 
retort.  When  coarsely  pulverized,  it  is  extensively  used  for  decol- 
orizing syrups  and  oils.  It  is  finely  powdered  for  pigment,  and  is 
much  used  in  making  leather  blacking,  where  the  calcium  phosphate 
and  carbonate  in  it  are  also  of  importance. 

Charcoal  from  soft  wood,  ground  very  fine,  is  sometimes  used  as 
a  pigment,  and  to  mix  with  other  blacks.  It  is  not  so  soft  and  fine 
as  lampblack. 

Graphite  is  employed  as  a  pigment  in  pencils,  crayons,  and  in 
stove-blacking.  It  also  forms  the  basis  of  a  protective  paint  for 
metal.  It  is  a  dull  black,  very  inert  and  permanent. 

Manganese  ores,  such  as  pyrolusite  (Mn02)  and  hausmannite 
(Mn304),  are  sometimes  powdered  for  pigments.  But  they  act  as 
"  dryers  "  when  used  with  oil,  and  are  rarely  used  in  paint. 

Black  lake,  made  from  logwood  decoction  and  potassium  bichro- 
mate with  copper  sulphate,  is  a  blue  black,  but  not  permanent. 

Tannate  of  iron  blacks,  derived  from  tannin  liquors,  copperas, 
and  alum,  also  fade  on  exposure  to  the  light. 


BROMINE  215 

REFERENCES 

Lehrbuch  der  Farbenfabrikation.     I.  G.  Gentele,  Braunschweig,  1880.     (Vie- 

weg  u.  Sohn.) 

Die  Erd-  Mineral-  und  Lackfarben.     Dr.  Mierzinski,  Weimar,  1881.     (Voigt.) 
Chemistry  of  Pigments.    J.  M.  Thomson.     Lecture  before  the  Society  for  the 

Encouragement  of  Arts,  Manufactures,  and   Commerce.     London,    1885. 

(W.  Trounce.) 

Fabrication  des  Couleurs.     Ch.  Er.  Guignet,  Paris,  1888. 
Oel  und  Buchdruckfarben.     Louis  E.  Andes,  Leipzig,  1889.     (Hartleben.) 
Die  Fabrikation  des  Ruses  und  der  Schwaerze.     Dr.  H.  Koehler,  Braunschweig, 

1889,  ( Vie wegu.  Sohn.) 

The  Chemistry  of  Paints  and  Painting.     A.  H.  Church,  London,  1890.     (See- 
ley.) 

Painters'  Oils,  Colours,  and  Varnishes.     George  H.  Hurst,  London,  1$92.    (Griffin 
and  Co.) 

Pigments,  Paints,  and  Painting.     George  Terry,  London,  1893.     (Spon.) 

Die  Fabrikation  der  Mineral-  und  Lackfarben.    Dr.  Josef  Bersch,  Leipzig,  1893. 
(Hartleben.) 

Die  Fabrikation  der  Erdfarben.     Dr.  Josef  Bersch,  Leipzig,  1893.     (Hartleben.) 

Handbuch  der  Farben-Fabrikation.     Dr.  S.  Mierzinski,  Leipzig,  1898.     (Hartle- 
ben.) 

Das  Ultramarine.     C.  Furstenau,  Wien,  1880.     (Hartleben.) 

Journal  of  the  Society  of  Chemical  Industry. 
1887,  719.     Rawlins.     (Ultramarine.) 

1890,  1137.     Wunder.     (Ultramarine.) 

1891,  709.     C.  O.  Weber.     (Chromium  Pigments.) 

Journal  of  American  Chemical  Society,  1880,  381.  —  H.  Endemann. 


BROMINE 

Bromine  is  widely  distributed  in  nature  as  bromides,  usually 
accompanying  common  salt  and  magnesium  chloride.  The  world's 
supply  is  obtained  from  "bittern,"  the  mother-liquor  of  the  salt 
industry.  Stassfurt  furnishes  about  two-thirds  of  the  supply,  and 
nearly  all  the  remainder  is  extracted  from  the  brines  found  in  Ohio, 
West  Virginia,  and  Kentucky,  along  the  Kanawha  and  Ohio  rivers. 
The  American  product  in  1893  was  about  348,000  pounds.  Small 
quantities  are  obtained  from  the  mother-liquors  of  the  Chili  salt- 
petre industry,  and  in  Europe  from  kelp. 

Bromine  is  present  in  the  bittern  as  magnesium  bromide,  and  to 
a  lesser  extent  as  sodium  bromide.  Associated  with  these  are  large 
quantities  of  magnesium  and  sodium  chlorides.  There  are  two  gen- 
eral methods  of  extracting  bromine  from  bittern,  —  the  continuous 
process,  chiefly  used  at  Stassfurt ;  and  the  periodic  process,  generally 
used  in  this  country. 


216     .         OUTLINES  OF  INDUSTRIAL   CHEMISTRY 

The  continuous  process  depends  on  the  decomposition  of  the 
magnesium  bromide  by  chlorine  gas.  A  sandstone  or  earthenware 
tower  is  filled  with  broken  brick  or  burned  clay  balls ;  chlorine  gas 
and  steam  are  introduced  at  the  bottom  of  the  tower,  and  rising 
between  the  balls,  meet  descending  streams  of  hot  bittern.  By  reac- 
tion between  the  chlorine  and  the  magnesium  bromide,  the  bromine 
is  set  free.  The  chlorine  stream  must  be  regular,  and  so  controlled 
that  no  excess  is  used  j  otherwise  some  bromine  chloride  is  formed. 
Part  of  the  bromine  dissolves  in  the  liquor  as  soon  as  set  free,  and 
this  liquor  flows  into  a  special  receiver,  heated  by  steam ;  here  it  is 
boiled  to  drive  out  the  bromine,  which,  together  with  water  vapor, 
passes  bac^:  into  the  tower,  entering  at  the  bottom,  and  mixing  with 
the  chlorine.  At  the  top  of  the  tower,  the  bromine  vapor  passes  out 
into  an  earthenware  worm-condenser,  which  empties  into  a  closed 
vessel.  An  outlet  pipe  from  the  top  of  this  receiver  passes  into 
a  small  tower,  filled  with  moist  iron  turnings  or  scrap  iron.  Any 
uncondensed  vapors  of  bromine,  passing  out  of  the  receiver,  combine 
with  the  iron  to  form  ferrous  bromide,  which  is  used  for  making 
potassium  bromide. 

In  this  process,  any  bromine  chloride  formed  in  the  tower  is 
decomposed  before  it  can  pass  into  the  condensing  worm,  by  the 
fresh  bittern  entering  at  the  top  of  the  tower.  Bromine  chloride  is 
a  very  volatile  liquid,  and  would  contaminate  the  bromine.  The 
exhausted  bittern  from  the  heating-vessel  goes  to  waste.  The  chlo- 
rine gas  necessary  is  made  in  special  stills  from  manganese  binoxide 
and  hydrochloric  acid. 

The  periodic  process  depends  on  the  following  reaction :  — 

MgBr2  +  2  H2S04  +  Mn02  =  MgS04  +  MnS04  +  2  H2O  +  2  Br. 

This  is  carried  on  in  sandstone  stills,  heated  by  steam.  A  charge 
of  pyrolusite,  sufficient  for  several  days,  is  put  into  the  still,  and  the 
bittern,  heated  to  60°  C.,  is  run  in.  The  quantity  of  sulphuric  acid 
to  be  added  is  very  carefully  gauged  with  each  charge  of  bittern  in 
order  that  none  of  the  magnesium  chloride  shall  be  decomposed. 
Usually,  a  little  of  the  magnesium  bromide  is  left  in  the  bittern, 
since  the  high  temperature  necessary  to  decompose  the  last  traces 
would  also  decompose  some  of  the  chloride,  which  would  form  bro- 
mine chloride,  and  contaminate  the  product.  The  bromine  distills 
over  into  a  condensing  worm,  as  above  described.  The  exhausted 
bittern  is  drawn  off  after  each  charge,  and  goes  to  waste.  At  the 
present  time,  considerable  potassium  chlorate  is  used  instead  of 
pyrolusite  for  the  oxidizing  agent.  This  is  especially  advantageous 


BROMINE  217 

if  the  bittern  contains  much  calcium  chloride,  since  only  one-half  as 
much  sulphuric  acid  is  necessary,  and  there  is,  consequently,  less 
difficulty  from  calcium  sulphate:  Neither  the  stills  nor  the  tower 
should  be  lined  with  pitch  or  tar,  since  these  substances  absorb  much 
bromine. 

The  crude  bromine  obtained  by  either  process  contains  some  bro- 
mine chloride,  lead  bromide  from  the  pipe-joints  and  connections, 
and  some  organic  matter.  It  is  purified  by  shaking  with  ferrous, 
sodium,  or  potassium  bromide,  and  re-distilling  from  glass  retorts. 
The  bromine  chloride  is  thus  decomposed,  and  the  salts  of  the  heavy 
metals  remain  in  the  still.  Very  pure  bromine  is  obtained  by  neu- 
tralizing with  barium  hydroxide  solution,  evaporating  to  dryness,  and 
calcining  at  a  red  heat.  The  barium  bromate  and  chlorate  formed  in 
the  neutralizing  are  decomposed  to  form  barium  bromide  and  chlo- 
ride. By  extracting  the  mass  with  alcohol,  the  bromide  is  dissolved. 
The  barium  bromide  obtained  by  evaporation  of  the  alcohol  is  de- 
composed with  pyrolusite  and  sulphuric  acid,  the  pure  bromine 
passing  to  the  condenser  as  vapor. 

Operations  with  liquid  bromine  must  be  carried  on  in  the  open 
air,  or  in  a  strong  draught.  If  inhaled,  the  vapors  are  suffocating, 
and  cause  great  irritation  of  the  air  passages.  The  liquid  attacks 
the  skin,  and  causes  sores  which  heal  very  slowly. 

Bromine  is  largely  used  in  making  certain  coal-tar  dyes,  such 
as  the  eosins ;  for  sodium  and  potassium  bromides ;  and  to  some 
extent  as  a  chemical  reagent,  and  for  making  organic  bromides.  It 
is  considered  dangerous  freight  by  transportation  companies,  and  so 
only  its  salts,  especially  potassium  bromide,  are  usually  shipped. 

"  Solidified  bromine  "  is  a  convenient  form  for  laboratory  work. 
This  consists  of  sticks  of  diatomaceous  earth,  pressed  with  size  or 
molasses,  burned  till  coherent,  and  soaked  in  liquid  bromine.  The 
porous  material  absorbs  from  50  to  75  per  cent  of  its  weight  of  the 
liquid. 

Potassium  bromide  is  made  by  decomposing  iron  bromide  with 
potassium  carbonate.  The  ferroso-ferric  bromide  (Fe8Br8),  made  by 
adding  more  bromine  to  ferrous  bromide,  is  usually  employed. 

Fe  -f  Br2  =  FeBr2. 

3  FeBr2  +  2  Br  =  Fe3Br8. 

Fe3Br8  +  4  K2C03  +  4  H20  =  Fe8(OH)8  +  8  KBr  +  4  C02. 
The  solution  is  filtered  and  evaporated,  yielding  cubical  crystals  of 
the  salt,  free  from  bromate,  which  is  always  formed  when  bromine 
is  neutralized  directly  with  alkali. 


218  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

Potassium  bromide  is  used  in  medicine  and  in  photography,  espe- 
cially in  the  preparation  of  silver  bromide  plates  and  films. 

Sodium  bromide  is  similar  to  the  potassium  salt,  is  used  for  the 
same  purposes,  and  is  made  in  the  same  way ;  but  it  does  not  crystal- 
lize so  well. 

REFERENCES 

Berichte  iiber  die  Entwickelung  der  chemischen  Industrie.  — A.  W.  Hofmann, 

1875,  129. 

Moniteur  scientifique,  1879,  905.  —  H.  S.  Welcome. 
Handbuch  der  Kali-Industrie,  E.  Pfeiffer,  321.    Braunschweig,  1887.    (Vieweg.) 


IODINE 

Iodine  is  obtained  from  the  ashes  of  seaweed,  and  from  the 
mother-liquors  of  the  Chili  saltpetre  industry. 

Along  the  coasts  of  France,  Scotland,  and  Norway,  seaweed  is 
collected  and  burned*  at  as  low  a  temperature  as  possible.  The  ash, 
called  kelp,  or  varec,  contains  from  0.5  to  1.5  per  cent  of  its  weight 
of  iodides  of  sodium  and  potassium.  It  is  lixiviated,  and  the  filtered 
solution  is  systematically  evaporated.  First,  sodium  sulphate,  and 
then  common  salt,  crystallizes.  By  further  evaporation,  sodium 
carbonate,  together  with  more  salt  and  potassium  chloride,  sepa- 
rates. The  mother-liquor  is  then  treated  with  sulphuric  acid  to 
decompose  the  alkali  sulphides  and  sulphites  formed  by  reduction  of 
the  sulphates  during  incineration.  This  precipitates  sulphur,  and 
the  sodium  sulphate  formed  crystallizes.  The  mother-liquor,  still 
holding  the  iodides  in  solution,  is  then  heated  to  60°  C.  in  iron 
retorts  with  lead  covers,  and  having  pipes  leading  to  condensers. f 
Small  quantities  of  pyrolusite  are  introduced  into  the  retort  period- 
ically, when  the  following  reaction  takes  place :  — 

2  Nal  +  3  H2S04  +  Mn02  =  MnS04  +  2  NaHS04  +  2  H20  +  I2. 

Pyrolusite  is  added  as  long  as  iodine  distills  off;  but  excess  must 
be  avoided,  lest  bromine  and  chlorine  be  set  free  from  the  salts 

*  By  burning  the  seaweed  in  closed  retorts,  the  loss  of  iodine  by  volatilization  is 
reduced. 

t  The  condensers,  called  udells,  are  bottle-shaped  vessels  of  earthenware,  arranged 
horizontally,  5  or  6  in  a  series,  the  neck  of  one  entering  the  bottom  of  the  next.  In 
the  lower  side  of  each  is  a  small  hole,  through  which  the  condensed  water  drains  off. 
Each  still  has  two  sets  of  udells,  which  are  left  in  position  during  repeated  charges  of 
the  still,  until  they  are  filled  with  solidified  iodine.  Recently  the  condensers  have 
been  made  of  seven  or  eight  lengths  of  plain  earthenware  pipe,  each  length  3  feet 
long  by  1£  feet  in  diameter,  and  the  joints  luted  with  clay. 


IODINE  219 

still  present  in  the  liquor,  and  combine  with  the  iodine  to  form 
tribrom-  or  trichlor-iodine  (IC13). 

Sometimes  the  iodine  liquor  is  decomposed  by  leading  chlorine 
gas  into  it,  the  same  as  in  making  bromine  (p.  216).  The  crude 
iodine  precipitates  as  a  paste,  and  is  washed  and  then  dried  on 
porous  plates.  Much  care  is  necessary  to  avoid  an  excess  of  chlo- 
rine, since  this  forms  volatile  iodine  trichloride  (IC13),  and  causes 
loss. 

By  heating  the  acidified  iodine  solution  with  ferric  chloride  or 
potassium  chlorate,  the  iodine  is  liberated  and  distills  off,  with 
some  water,  and  no  trichloride  is  formed,  thus :  — 

a)   2  Nal  +  2  FeCl3  =  2  FeCL,  +  2  NaCl  +  I2. 

6)   6  Nal  +  KC103  +  3  H2O  =  6  NaOH  +  KC1  +  61. 

Another  method  is  to  mix  the  kelp  with  a  little  water  and  sul- 
phuric acid,  and  to  add  potassium  bichromate. 

6  NaI+10  H2S04+K2Cr207  =  6  NaHS04+K2Cr2(S04)4+7  H20+6 1. 

The  precipitated  iodine  is  washed,  dried,  and  sublimed. 

It  has  been  proposed  to  heat  the  kelp  directly  with  powdered 
bichromate,  decomposition  taking  place  at  a  red  heat,  and  the  iodine 
subliming :  — 

6  KI  +  K2O207  =  4  K20  +  O203  +  61. 

Numerous  other  processes  have  been  devised  for  obtaining  iodine 
from  kelp,  some  of  which  are  in  use. 

The  recovery  of  iodine  from  the  mother-liquors  of  Chili  saltpetre 
is  now  most  important.  The  iodine  is  chiefly  in  the  form  of  sodium 
iodate  (NaI08),  and  the  process  depends  on  the  following  reaction :  — 

2  NaI03  +  5  S02  +  4  H20  =  Na2S04  +  4  H2SO4  +  I2. 

In  practice,  the  sulphur  dioxide  is  used  in  the  form  of  sodium 
bisulphite  solution,  containing  some  neutral  sulphite.  This  is  made 
immediately  before  use  by  leading  sulphur  dioxide  gas  into  sodium 
carbonate  solution  until  the  liquid  contains  one  part  of  neutral  sul- 
phite to  two  of  acid  sulphite.  The  requisite  quantity  of  this  acid 
sulphite  liquor  is  added  to  the  mother-liquor,  and  thoroughly  agi- 
tated ;  the  precipitated  iodine  is  collected  on  filters  made  of  coarse 
bagging  or  canvas,  and  after  washing  is  pressed  heavily  to  remove 
excess  of  water. 

The  reaction  is  probably  as  follows :  — 

2  NaI03  +  3  Na2S03  +  2  NaHS03  =  5  NaaS04  +  I,  +  H20. 


220  OUTLINES  OF   INDUSTRIAL   CHEMISTRY 

But  since  some  sodium  iodide  is  also  present,  the  excess  of 
bisulphate  employed  decomposes  it  according  to  the  reaction  :  — 

NaI03  +  Nal  +  2  NaHS03  =  2  NajS04  +  I2  +  H20. 

Sometimes  the  iodine  is  precipitated  as  cuprous  iodide  (Cu2I2)  by 
adding  copper  sulphate  and  sodium  bisulphite  to  the  mother-liquors, 
but  this  is  now  less  frequently  done  than  formerly.  The  cuprous 
iodide  was  shipped  to  Europe,  and  used  to  make  potassium  iodide 
by  treating  with  potassium  carbonate. 

The  liquors  from  which  the  iodine  has  been  separated  are  re- 
turned to  the  lixiviation  tanks  for  the  treatment  of  the  crude 
"caliche"  (p.  120). 

The  crude  iodine  obtained  by  any  of  the  above  processes  is  puri- 
fied by  re-subliming  in  iron  retorts,  the  vapors  being  condensed  in 
earthenware  receivers.  The  temperature  of  the  retorts  must  be  very 
low  in  order  to  form  large  crystals,  and  the  condensers  must  not  be 
so  cool  as  to  cause  sudden  condensation  of  the  vapors. 

The  chief  uses  of  iodine  are  in  the  manufacture  of  coal-tar  dyes 
and  organic  compounds,  and  in  medicinal  preparations. 

The  most  important  iodine  derivative  is  potassium  iodide  (KI). 
This  is  made  in  several  ways  :  — 

(a)  Iodine  may  be  dissolved  in  a  caustic  potash  or  carbonate 
solution,  the  solution  evaporated  to  dryness,  and  the  mixture  of 
iodide  and  iodate  so  obtained  calcined  with  powdered  charcoal  at  a 
low  red  heat,  to  decompose  the  latter  salt. 

61  +  6  KOH  =  5  KI  +  KI03  +  3  H20. 


The  calcined  mass  is  lixiviated,  filtered,  and  crystallized.  Very  pure 
materials  are  needed  in  this  process. 

(6)  A  better  method  is  to  form  ferroso-ferric  iodide,  and  decom- 
pose this  with  pure  potassium  carbonate.  Metallic  iron  is  dissolved 
by  digesting  with  iodine  and  water,  forming  ferrous  iodide,  which  is 
then  treated  with  sufficient  iodine  to  form  the  ferroso-ferric  salt  :  — 

Fe  +  2  1  =  FeI2. 

3FeI2  +  2I  =  Fe3I8. 

Fe3I8  -{-  4  K2C03  +  4  H20  =  Fe3(OH)8  +  8  KI  +  4  C02. 

This  method,  if  carefully  worked,  yields  a  very  pure  salt,  entirely 
free  from  potassium  iodate.  The  precipitated  ferroso-ferric  hy- 
droxide is  granular,  and  more  easily  washed  than  is  ferrous 
hydroxide, 


PHOSPHORUS  221 

(c)  Barium  iodide  is  made  by  agitating  barium  sulphide  solution 
with  iodine.     The  clear  solution  is  then  boiled  with  potassium  sul- 
phate solution,  the  precipitated  barium  sulphate  filtered  off,  and  the 
filtrate  evaporated  until  the  potassium  iodide  crystallizes :  — 
BaS  +  I2  =  BaI2  +  S. 
BaI2  +  K2S04  =  BaS04  +  2  KL 

Potassium  iodide  is  chiefly  used  in  medicine  as  an  alterative  and 
diuretic.  A  small  quantity  is  used  in  photography. 

Lead,  mercury,  and  ferrous  iodides  are  used  to  a  small  extent  in 
medicine,  but  these  are  not  important. 

REFERENCES 
Wagner's  Jahresbericht  iiber  die  Leistungen  der  chemischen  Technologic  :  — 

1879,  337.     G.  Langbein.     (Jod-Gewinnung  in  Chili.) 

1879,  334.     E.  Sobering.     (Jodkalium.) 
Journal  of  the  Society  of  Chemical  Industry  :  — 

1893,  128.     J.  Buchanan.     (Extraction  of  Iodine  in  Chili.) 

PHOSPHORUS 

The  discovery  of  phosphorus,  about  1675,  is  attributed  to  an 
alchemist,  Brand,  at  Hamburg.  Urine  which  had  been  evaporated 
to  a  thick  syrup,  was  heated  in  an  earthenware  retort  with  sand,  the 
phosphorus  distilling  off.  It  was  known  only  as  a  chemical  curios- 
ity until  Scheele,  in  1775,  made  it  from  bone-ash;  soon  after  it 
assumed  some  commercial  importance.  Bone-ash  is  still  a  leading 
source,  but  recently  the  mineral  phosphates,  being  cheaper,  have 
been  employed. 

Ground  bone-ash  is  treated  with  sulphuric  acid,  forming  calcium 
sulphate  and  mono-calcium  phosphate  (p.  143)  ;  the  latter  is  leached 
out  of  the  sulphate  with  hot  water.  The  solution  is  decanted,  and 
evaporated  to  a  thick  syrup  in  lead  pans,  pulverized  charcoal  or  coke 
is  stirred  in,  and,  after  drying  in  iron  pans  over  direct  fire,  the  mass 
is  put  into  small  earthenware  retorts,  several  of  which  are  placed  in 
a  furnace  at  one  time.  These  are  heated  moderately  at  first,  and  the 
mono-calcium  phosphate  decomposes,  forming  calcium  metaphosphate 
[Ca(P03)2].  The  temperature  is  then  raised,  and  the  carbon  decom- 
poses the  metaphosphate,  forming  tricalcium  phosphate,  phosphorus, 
and  carbon  monoxide. 

The  reactions  involved  are  as  follows :  — 

1)  Ca3(P04)2  +  2  H2S04  =  CaH4(P04)2  +  2  CaS04. 

2)  CaH4(P04)2  =  2  H20  +  Ca(P03)2. 

3)  3  Ca(P03)2  +  10  C  =  Ca3(P04)2  +  P4  +  10  CO. 


222  OUTLINES  OF   INDUSTRIAL   CHEMISTRY 

Thus  only  two-thirds  of  the  phosphorus  is  obtained  free.  But  by 
adding  silica  to  the  mixture  complete  decomposition  results :  — 

4)  2  Ca(P03)2  +  10  C  +  2  Si02  =  2  CaSi03  +  P4  +  10  CO. 

The  distillation  is  very  slow,  requiring  4  or  5  days.  The  phospho- 
rus vapor  is  condensed  in  closed  vessels,  and  collects  under  hot 
water  as  a  thick  liquid ;  it  is  purified  as  described  below. 

A  more  direct  process,1*  now  largely  employed,  consists  in  decom- 
posing mineral  or  bone  phosphates  with  sufficient  acid  to  convert  all 
of  the  calcium  to  sulphate,  and  a  solution  of  free  phosphoric  acid  is 
formed.  This  solution  is  filtered  through  a  bed  of  ashes  supported 
on  a  grating  in  a  lead-lined  wooden  tank,  and  the  sulphate  washed 
with  water.  The  solution  of  phosphoric  acid  is  concentrated  to  a 
density  of  from  65°  to  100°  Tw.  in  lead-lined  tanks,  heated  by  high- 
pressure  steam  coils.  An  effective  stirrer  is  used  to  prevent  the 
calcium  sulphate,  which  separates,  from  depositing  on  the  coils. 
The  solution  is  drawn  into  cooling  tanks,  where  nearly  all  the 
sulphate  separates.  The  concentrated  phosphoric  acid  is  mixed 
with  sawdust,  charcoal,  or  coke  powder,  and  dried  in  an  iron  pot  or 
muffle.  Sawdust  is  used  when  the  solution  is  concentrated  to 
65°  Tw.,  but  for  charcoal  or  coke  a  thick  syrup  is  necessary.  The 
dried  mass  is  filled  into  earthenware  retorts,  each  holding  about  25 
pounds ;  24  of  these  retorts  are  heated  in  one  furnace.  From  each 
retort,  a  pipe  leads  to  a  trough  containing  water,  and  dips  just  below 
the  surface  of  the  water.  The  temperature  is  raised  to  a  white  heat. 
The  distillation  requires  about  16  hours,  the  melted  phosphorus  col- 
lecting in  the  troughs  under  the  water.  The  reactions  involved  are 
as  follows :  — 

1)  Ca3(P04)2  +  3  H2S04  =  3  CaS04  +  2  H3P04. 

2)  2  H3P04  =  2  HP03  +  2  H20. 

3)  4  HP03  +  12  C  =  12  CO  +  2  H2  +  P4. 

A  continuous  process  for  the  direct  production  of  phosphorus 
from  calcium  phosphates  by  means  of  the  electric  furnace  has  been 
devised  by  Eeadman,  Parker,  and  Robinson.f  An  intimate  mixture 
of  carbon,  phosphate,  and  flux  is  heated  in  a  tightly  covered  electric 
furnace,  having  an  outlet  pipe  leading  to  a  condenser,  into  which  the 
phosphorus  and  gas  pass.  The  residue  fuses  to  a  slag  in  the  fur- 
nace, and  is  tapped  off  at  intervals,  fresh  charges  being  introduced 
without  interrupting  the  electric  current.  This  method  avoids  the 

*  J.  B.  Readman,  Thorpe's  Dictionary  of  Applied  Chemistry,  Vol.  Ill,  185. 
t  J.  B.  Readman,  I.e. 


PHOSPHORUS  223 

use  of  sulphuric  acid,  the  concentration  and  handling  of  phosphoric 
acid,  uses  no  earthenware  retorts,  and  saves  time ;  it  is  further 
claimed  that  less  coal  is  used. 

The  crude  phosphorus  made  by  any  of  the  above  processes  con- 
tains sand,  carbon,  clay,  and  other  impurities.  It  is  purified  by 
melting  under  warm  water,  and  straining  through  canvas  bags; 
formerly  chamois  leather  was  used.  Or  it  is  redistilled  from  iron 
retorts.  Sometimes  it  is  treated  with  a  3  per  cent  solution  of  potas- 
sium bichromate  and  its  equivalent  of  sulphuric  acid,  in  a  lead-lined 
agitator  which  is  heated  by  steam  coils.  After  a  couple  of  hours 
agitation,  the  phosphorus  is  nearly  transparent,  and  of  a  light  yel- 
low color.  It  is  washed  with  hot  water,  filtered  through  canvas 
bags,  and  moulded  into  "  sticks  "  by  pouring  into  glass  or  tin  tubes 
placed  in  cold  water.  For  shipment,  phosphorus  is  packed  in  water 
in  tin  boxes,  the  lids  of  which  are  tightly  soldered. 

Yellow  or  ordinary  phosphorus  is  a  pale  yellow,  translucent,  wax- 
like  mass  of  1.82  specific  gravity,  very  inflammable,  and  combining 
directly  with  oxygen,  sulphur,  and  the  halogens.  It  melts  at  43.3° 
C.  under  water,  and  at  30°  C.  when  dry ;  it  distills  at  269°.*  It  is 
very  soluble  in  carbon  disulphide,  sulphur  chloride,  and  phosphorus 
trichloride,  slightly  so  in  caustic  soda  solution,  but  insoluble  in 
water.  It  is  exceedingly  poisonous,  less  than  0.15  gram  being  a 
fatal  dose.  Persons  working  continuously  with  yellow  phosphorus 
are  subject  to  necrosis,  usually  appearing  first  in  the  jawbones. 

The  chief  uses  of  yellow  phosphorus  are  in  making  matches  and 
phosphor-bronze,  and  for  rat  poison. 

Amorphous  or  red  phosphorus  is  made  by  heating  the  yellow 
variety  for  several  hours  in  closed  retorts  at  250°  C.  If  an  auto- 
clave be  employed,  and  the  temperature  raised  to  300°  C.,  the  press- 
ure inside  the  vessel  makes  the  process  much  more  rapid.  The 
hard  mass  thus  produced  is  ground  under  water,  and  the  powder 
boiled  with  caustic  soda  solution  to  remove  any  unchanged  yellow 
phosphorus.  Carbon  disulphide  is  sometimes  used  instead  of  caus- 
tic soda,  but  this  is  expensive  and  easily  inflamed.  After  boiling  in 
water,  filtering,  and  drying  by  steam  heat,  the  amorphous  phospho- 
rus is  packed  dry.  Eed  phosphorus  is  a  reddish  brown,  opaque 
substance,  having  a  specific  gravity  of  2.25.  It  is  not  affected  by 
heating  in  the  air  until  the  temperature  reaches  260°  C.,  at  which 
point  it  inflames.  By  heating  in  an  atmosphere  of  nitrogen  or  car- 
bon dioxide,  it  distills,  returning  to  the  yellow  variety.  It  is  insol- 
uble in  carbon  disulphide,  caustic  soda,  and  in  water,  and  is  not 
*  J.  B.  Readman,  I.e. 


224  OUTLINES  OF   INDUSTRIAL  CHEMISTRY 

poisonous.     The  chief  use  of  red  phosphorus  is  in  the  manufacture 
of  "  safety  matches." 

MATCHES 

In  about  1812,  the  so-called  "  chemical  matches  "  were  invented. 
Sticks  were  dipped  in  melted  sulphur,  and  the  "  head  "  coated  with 
a  mixture  of  sugar  and  potassium  chlorate.  It  was  fired  by  dipping 
into  a  bottle  containing  asbestos  moistened  with  sulphuric  acid. 

Friction,  or  lucifer,  matches  were  invented  in  1827,  in  England. 
The  heads  were  a  mixture  of  antimony  trisulphide  and  potassium 
chlorate,  made  into  a  stiff  paste  with  water  and  gum.  They  were 
ignited  by  rubbing  on  sand  or  emery  paper.  The  antimony  trisul- 
phide was  soon  replaced  by  phosphorus,  and  the  potassium  chlorate 
by  nitre.  At  the  present  time,  lead  peroxide,  red  lead,  or  man- 
ganese dioxide  are  used  instead  of  nitre  as  the  oxidizing  substance. 
Chlorates  are  used,  but  sparingly,  since  they  form  explosive  mixtures. 

Soft  wood,  generally  pine  or  spruce,  is  cut  by  machines  to  form 
the  sticks,  which  are  thoroughly  kiln-dried.  They  are  then  fixed  in 
a  frame  so  that  each  stick  stands  alone,  and  the  end  of  each  stick  is 
well  soaked  in  melted  sulphur,  paraifine,  or  stearic  acid.  The  igniting 
mixture  is  made  by  slowly  stirring  phosphorus  into  a  warm  solution 
of  dextrine  or  glue ;  the  oxidizing  materials  are  then  added,  and  the 
paste  stirred  until  cold.  It  is  frequently  colored  with  ultramarine, 
lead  chromate,  chalk,  or  lampblack.  It  is  then  spread  evenly  in  a 
thin  layer  on  a  table,  and  the  prepared  sticks  dipped  into  it  once  or 
twice.  .After  drying,  the  heads  are  sometimes  dipped  in  thin  shel- 
lac or  other  varnish,  to  protect  them  from  the  moisture  in  the  air. 

Safety  matches  are  made  without  yellow  phosphorus.  The  match 
head  is  generally  sulphur,  or  antimony  trisulphide,  with  potassium 
chlorate,  or  bichromate,  as  the  oxidizing  material.  Sometimes  red 
lead,  lead  peroxide,  or  manganese  dioxide  is  used  as  a  part  of  the 
oxidizing  material.  The  surface  upon  which  the  match  must  be 
lighted  is  coated  with  a  mixture  of  red  phosphorus,  antimony  trisul- 
phide, and  dextrine,  or  glue.  Powdered  glass  or  emery  is  used  to 
increase  the  friction. 

The  compositions  used  on  matches  are  carefully  guarded  as  trade- 
secrets,  and  are  different  in  different  factories.  One  is  given  as 
follows :  — 


HEAD  COMPOSITION 

KC103 5  parts 

K2Cr207 2  parts 

Glass  Powder 3  parts 

Gum 2  parts 


EUBBING  SURFACE 

Sb2S3 5    parts 

Red  Phosphorus  ...        .3    parts 

Mn02 Imparts 

Glue 4    parts 


BORIC  ACID  225 

The  friction  of  the  match  head  on  the  prepared  snrface  develops 
sufficient  heat  to  convert  a  little  of  the  red  phosphorus  to  the  yellow 
variety,  which  at  once  combines  with  some  of  the  potassium  chlorate 
and  antimony  sulphide,  evolving  enough  heat  to  inflame  the  mixt- 
ure on  the  head. 

To  prevent  the  burned  stems  from  smouldering,  the  sticks  are 
sometimes  soaked  in  a  solution  of  magnesium  sulphate,  alum,  or 
sodium  phosphate  before  making  the  head. 

In  some  countries,  notably  Switzerland,  the  manufacture  and  sale 
of  matches  containing  yellow  phosphorus  is  prohibited. 

REFERENCES 

Chemical  News,  1879,  147.    J.  B.  Readman.     (Manufacture  of  Phosphorus.) 
Chemiker-Zeitung,  1881,  196.     A.  Rossel.     (Matches  without  Phosphorus.) 
Journal  of  the  Society  of  Chemical  Industry  :  — 

1890,  163,  473.     J.  B.  Readman.     (Manufacture  of  Phosphorus.) 

1891,  445.    J.  B.  Readman.     (Manufacture  of  Phosphorus. ) 


BORIC   ACID 

Boric  acid,  B(OH)3,  occurs  in  volcanic  regions,  especially  in  Tus- 
cany, as  a  constituent  of  the  vapors,  called  soffioni,  which  escape 
from  hot  springs  and  from  openings  in  the  ground,  called  fumeroles. 
In  some  places  the  water  has  evaporated  from  the  fumeroles,  and  the 
boric  acid  has  crystallized,  forming  the  mineral  sassolite.  Combina- 
tions of  boric  acid  with  sodium,  magnesium,  and  calcium  are  found 
in  various  places :  as,  tinkal  (native  borax),  Na2B407  •  10  H20 ;  bora- 
cite,  2  (Mg3B8015),  MgCl2 ;  borocalcite,  CaB407  -  6  H20 ;  and  borona- 
trocalcite  (ulexite),  ]STa2B407,  (2  CaB407),  18  H20. 

In  Tuscany,  natural  or  artificial  ponds  (lagoons)  are  formed 
around  the  fumeroles,  or  a  series  of  masonry  basins  or  tanks  are 
constructed  over  them,  and  the  soffioni  made  to  bubble  through 
water  in  these,  thus  washing  most  of  the  boric  acid  from  the  vapors. 
These  tanks  are  so  arranged  that  the  water  from  one  flows  into 
another  at  a  lower  level ;  in  the  final  basin,  a  solution  containing 
about  2  per  cent  boric  acid  is  obtained.  The  solution  is  evaporated, 
either  in  lead-lined  vessels,  heated  by  the  steam  from  the  fumeroles, 
or  in  cement-lined  tanks,  having  coils  through  which  the  steam 
passes.  Calcium  sulphate  deposits  freely  during  the  evaporation  of 
the  solution,  which  is  concentrated  to  1.08  specific  gravity.  It  is 
then  crystallized  in  lead-lined  wooden  vats.  The  crystals  are  drained 
for  some  hours,  and  dried  on  a  floor  also  heated  by  steam  from  the 
Q 


226  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

fumeroles.  The  crude  boric  acid  thus  formed  is  purified  by  re- 
crystallization. 

In  many  places  in  Tuscany,  bored  wells  have  been  sunk  from 
200  to  300  feet,  and  the  vapors  escape  from  these  as  from  the  natural 
fumeroles. 

Considerable  boric  acid  is  made  in  California  and  Nevada  by 
decomposing  the  borax  found  there,  with  hydrochloric  or  with  sul- 
phuric acid.  The  borocalcite,  found  in  Chili,  is  decomposed  in  the 
same  way. 

Much  boric  acid  is  made  from  the  boracite  in  the  Stassfurt  salts. 
The  mineral  is  crushed,  and  treated  with  just  enough  hydrochloric 
acid  to  decompose  it.  A  rather  vigorous  reaction  takes  place,  and 
the  mass  becomes  pasty.  It  is  dissolved  in  boiling  water,  and  care- 
fully tested  for  free  hydrochloric  acid ;  if  none  is  present,  the  solu- 
tion of  boric  acid  is  decanted  from  the  sediment  of  clay  and  sand,  or 
filtered  through  linen  bags,  and  is  crystallized  in  lead-lined  or  iron 
tanks.*  Sulphuric  acid  is  also  used  to  decompose  the  boracite,  in 
which  case  the  mother-liquors  from  the  boric  acid  contain  magne- 
sium sulphate;  this  is  recovered  as  Epsom  salt.  The  following 
reactions  are  involved  :  — 

1)  (2  Mg3B8015),  MgCl2  +  12  HC1  +  18  H2O  =  7  MgCl2  +  16  B(OH)3. 

2)  (2  Mg3B8015),  MgCl2  +  7  H2S04  +  18  H20 

=  7  MgS04  +  2  HC1  +  16  B(OH)3. 

The  actual  quantity  of  acid  used  is  determined  for  each  lot  of  salt. 

Boric  acid  forms  pearly  wnite,  laminated  crystals,  very  slightly 
soluble  in  cold  water,  but  dissolving  readily  in  hot  water.  It  has 
but  little  taste.  When  heated,  it  loses  water,  and  at  140°  C.  forms 
pyroboric  acid,  H2B407.  At  a  red  heat,  all  the  water  is  expelled, 
and  boric  anhydride  (B203)  results ;  this  is  stable  and  non-volatile, 
even  at  high  temperatures.  Consequently,  it  will  decompose  nearly 
all  metallic  sulphates,  carbonates,  and  nitrates  when  fused  with 
them,  forming  metallic  borates.  Hence  it  is  used  as  a  flux.  Boric 
acid  is  chiefly  used  in  the  preparation  of  borax ;  in  enamels  and 
glazes  for  pottery ;  in  making  Guignet's  green ;  as  an  antiseptic  in 
medicine  and  surgery ;  and  for  preserving  fish,  meat,  and  milk. 

Borax,  sodium  biborate,  Na2B407,  is  the  only  important  salt  de- 
rived from  boric  acid.  It  is  found  native  in  Thibet,  Ceylon,  and 
California.  But  little  is  known  of  the  method  of  preparing  borax 

*F.  Wittig  (Zeit.  angew.  Chem.,  1888,  483),  recommends  iron  crystallizing 
tanks,  because  lead-lined  vessels  buckle  and  leak,  owing  to  the  changes  of  tempera- 
ture. The  iron  soon  becomes  polished,  and  yields  perfectly  clean  crystals. 


BORIC   ACID  227 

in  Thibet.  It  conies  from  that  country  as  tinJcal,  an  impure,  crys- 
tallized borax,  containing  lime,  magnesia,  sulphates,  and  chlorides, 
and  a  greasy  substance  added  presumably  to  protect  the  crystal 
from  efflorescence  and  breakage.  The  tinkal  is  purified  by  dissolv- 
ing in  hot  water,  and  adding  lime-water  and  calcium  chloride,  to 
precipitate  the  grease  as  lime  soap.  After  filtering,  the  borax  is 
crystallized  by  concentrating  the  solution. 

A  large  quantity  of  borax  is  obtained  from  the  water  of  Borax 
Lake,  in  California ;  and  from  certain  marshes  in  California  and  in 
Nevada,  where  borax,  together  with  sodium  carbonate,  sulphate,  and 
chloride,  forms  an  efflorescence  or  crust  on  the  surface  of  the  marsh, 
owing  to  the  evaporation  of  water.  The  mud  of  these  marshes 
often  contains  crystals  of  borax  and  soda,  which  are  picked  out  by 
hand ;  it  is  leached  with  water  to  dissolve  the  finer  crystals. 

In  San  Bernardino  County,  California,  there  is  a  vein  of  mineral, 
consisting  chiefly  of  calcium  borate  and  carbonate,  which  is  exten- 
sively worked  for  boric  acid  and  borax.  A  similar  deposit  is  found 
in  Oregon.  The  calcium  borate  is  washed  to  remove  soluble  sul- 
phates and  chlorides,  and  then  boiled  with  a  slight  excess  of  sodium 
carbonate.  The  clarified  liquid  is  allowed  to  crystallize,  and  a  crude 
borax,  containing  Glauber  salt,  is  obtained.  This  is  redissolved  to 
form  a  solution  of  30°  Be.,  measured  hot,  a  little  sodium  hypochlorite 
is  added,  and  the  liquid  is  run  into  closed  crystallizing  tanks,  where 
it  cools  very  slowly.  When  the  temperature  falls  to  33°  C.,  the 
mother-liquor  is  drawn  off  to  prevent  contaminating  the  borax 
crystals  with  the  Glauber's  salt,  which  separates  below  that  tem- 
perature, and  for  which  the  mother-liquor  is  then  worked. 

A  deposit  of  borocalcite  called  pandermite  is  found  in  Asia 
Minor,  and  is  worked  in  a  similar  manner.  » 

The  crude  borax  is  purified  by  recrystallization  in  lead-lined 
tanks.  In  order  to  form  good  crystals,  the  solution  must  cool  very 
slowly,  and  the  tank  should  be  tightly  closed  to  prevent  the  forma- 
tion of  a  surface  crust.  In  crystallizing  borax,  a  small  excess  'of 
sodium  carbonate  (5  per  cent.),  in  the  solution  is  advantageous ;  but 
more  than  this  results  in  the  formation  of  neutral  sodium  borate, 
NaB02,  4  H20,  according  to  the  reaction  :  — 

Na2B4O7  -|-  Na2C03  =  4  NaB02  +  C02. 

Much  of  the  boric  acid  produced  in  Italy  is  converted  to  borax, 
by  dissolving  it  in  a  boiling  solution  of  sodium  carbonate.  The 
solution  is  then  concentrated  to  22°  B&,  at  104°  C.,  and  after  settling, 
is  run  into  the  crystallizing  tanks,  which  are  shallow  and  open,  so 


228  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

that  the  borax  deposits  within  three  days ;  but  for  recrystallization, 
deep  tanks,  tightly  covered,  and  lagged  to  prevent  radiation  of  the 
heat,  are  used.  The  crystallization  requires  from  16  to  18  days,  and 
the  crystals  formed  are  usually  large. 

Borax  comes  in  trade  in  two  forms ;  common  or  prismatic  borax, 
Na2B407  -  10  H2O,  and  octahedral  borax,  Na2B407  •  5  H2O.  The  for- 
mer is  produced  by  crystallizing  from  a  solution  of  22°  Be.,  which  is 
permitted  to  cool  to  27°  C. ;  the  latter  is  obtained  when  a  solution  of 
common  borax  is  concentrated  to  30°  Be.,  and  cooled  only  to  56°  C. 

Prismatic  borax  forms  large,  monoclinic  crystals,  and  effloresces 
in  the  air  j  it  melts  in  its  water  of  crystallization  when  heated,  after- 
wards swelling  greatly,  forming  a  spongy  mass,  but  at  a  red  heat 
fusing  and  becoming  transparent  and  glassy. 

Octahedral  borax  forms  regular  octahedrons,  permanent  in  dry 
air,  but  absorbing  moisture  on  exposure,  and  passing  into  the  pris- 
matic variety.  It  fuses  readily  without  intumescence,  and  is  there- 
fore preferred  as  a  flux  and  for  brazing  and  soldering. 

Borax  is  used  as  a  flux  in  welding  and  brazing  metals ;  in  enamel 
and  glazes  for  metal  ware  and  pottery ;  in  laundry  work,  and  in 
starch  to  increase  the  gloss ;  in  soaps,  especially  those  intended  for 
use  in  hard  water ;  for  the  preservation  of  meat ;  as  a  mordant  in 
dyeing ;  for  the  ungumming  of  raw  silk ;  in  medicine,  and  in  phar- 
macy ;  and  with  casein  for  the  preparation  of  paste. 

REFERENCES 

Hofmann's  Bericht  iiber  die  Entwickelung  der  Chemischen  Industrie.    1875, 

324,  343. 

Handbuch  der  Kali-Industrie.     E.  Pfeiffer,  Braunschweig,  1887.     (Boracit.) 
Chemiker-Zeitung :  — 

1879,  46.     F.  Filsinger.     (Boric  Acid  from  Boracite.) 

1887,  605.     L.  Darapsky.     (Borax  in  Chili. ) 

Third  Annual  Report  of  the  California  State  Mineralogist,  1883. 
Zeitschrift  f iir  angewandte  Chemie  :  — 

1888,  483.     F.  Witting.     (Borax  from  Boronatrocalcite.) 

1891,  367. 

1892,  241.     Dr.  Scheuer.     (Boric  Acid  and  Borax  Industry.) 
Journal  of  the  Society  of  Chemical  Industry  :  — 

1889,  857.     C.  N.  Hake.     (Borax  Lake  in  California.) 
1892,  683.     Dr.  Scheuer. 

Engineering  and  Mining  Journal :  — 

53,  8.     J.  F.  Kemp.     (Borax.) 

54,  247. 

Die  Stassfurter  Kali-Industrie.     G.  Lierke,  Wien,  1891. 


ARSENIC   COMPOUNDS  229 

ARSENIC  COMPOUNDS 

Arsenious  acid,  white  arsenic,  or  arsenic  trioxide  (As203),  is  the 
most  important  arsenic  derivative.  It  is  made  by  roasting  arsenical 
pyrites  (mispickel),  FeAsS ;  or  as  a  by-product  in  the  preparation  of 
zaffre  from  cobaltite  (CoAsS),  or  smaltite  (CoAs2),  and  in  roasting 
certain  arsenical  tin  ores  before  smelting. 

The  roasting  is  done  in  reverberatory  furnaces,  and  the  vapors  of 
white  arsenic  sublime  off,  and  are  condensed  as  a  powder  in  long 
horizontal  canals,  or  in  chambers.  The  crude  product  is  purified  in 
a  small  reverberatory  furnace,  fired  with  coke,  or  in  cast-iron  pots,  a 
number  of  which  are  set  in  a  furnace,  all  being  connected  with  a 
single  condensing  chamber  or  canal.  Directly  over  the  pot  an  iron 
drum  or  cylinder  is  often  placed,  from  the  top  of  which  a  short  pipe 
leads  to  the  condensing  chamber. 

After  resubliming,  the  oxide  is  a  white  granular  powder,  which 
is  usually  ground  before  packing  for  market ;  or,  by  a  second  subli- 
mation under  slight  pressure  in  an  atmosphere  of  arsenious  acid,  it 
is  obtained  in  an  amorphous  or  vitreous  state.  For  this  the  pot  is 
heated  red-hot,  and  the  "  arsenic  meal "  introduced  through  an  open- 
ing in  the  cap  of  the  drum,  which  is  then  closed.  The  arsenic  vapor 
rises  into  the  drum,  and  condenses  on  its  walls  as  a  transparent  layer 
of  "  arsenic  glass." 

White  arsenic,  or,  as  it  is  commonly  called,  arsenic,  comes  in 
commerce  as  a  powder,  and  as  a' "glass."  On  standing,  the  latter 
changes  to  a  crystalline  state,  and  becomes  white,  opaque,  and  porce- 
lain-like in  structure.  It  has  no  odor,  and  a  very  slight  metallic 
taste,  is  difficultly  soluble  in  water,  and  vaporizes  without  melting 
when  heated  in  the  open  air.  It  is  used  in  glass-making ;  when  dis- 
solved in  glycerine,  as  a  mordant  in  calico  printing;  in  making 
various  pigments ;  for  preparing  fly  and  rat  poisons ;  as  a  preserv- 
ative for  green  hides;  for  the  manufacture  of  arsenic  salts  and 
preparations ;  in  medicine ;  and  formerly,  to  a  great  extent,  in  the 
preparation  of  aniline  from  nitrobenzene. 

Arsenic  acid,  H3As04,  is  prepared  by  heating  4  parts  arsenic  tri- 
oxide with  3  parts  concentrated  nitric  acid  (1.35  sp.  gr.),  and  evapo- 
rating the  solution  to  a  thick  syrup,  in  which  form  it  is  usually  sent 
to  market.  By  evaporating  it  to  dryness,  and  igniting  at  a  red  heat, 
arsenic  pentoxide,  As205,  a  hygroscopic  body,  is  formed. 

Arsenic  acid  attacks  the  skin,  producing  blisters,  but  is  less  poi- 


!-»    O     A      ..T 


230  OUTLINES  OF  INDUSTRIAL   CHEMISTRY 

sonous  than  arsenious  acid.  It  is  chiefly  used  in  calico  printing, 
but  was  formerly  much  employed  as  an  oxidizing  agent  in  making 
certain  coal-tar  dyes  (rosanilines). 

Sodium  arsenate,  Na2HAs04,  is  made  by  heating  white  arsenic 
with  sodium  nitrate,  or  by  dissolving  white  arsenic  in  sodium  car- 
bonate solution,  adding  some  sodium  nitrate,  evaporating  to  dryness, 
and  calcining  the  mass.  By  dissolving  in  water,  and  crystallizing, 
the  salt  Na2HAs04  •  12  H2O,  is  obtained.  This  usually  contains  some 
NaH2As04  •  H2O  (binarsenate). 

It  is  used  as  a  substitute  for  the  "dung-bath"  in  dyeing  ali- 
zarines, and  in  calico  printing,  to  prevent  discoloration  of  the  white 
parts  of  the  pattern  by  rendering  the  excess  of  mordant  insoluble,  so 
that  it  does  not  "  bleed,"  i.e.  diffuse  into  the  white  portions  of  the 
cloth. 

Sodium  arsenite,  NaAs02  (meta-arsenite),  is  prepared  by  neutral- 
izing arsenious  acid  with  sodium  carbonate,  or  hydroxide  solution, 
and  boiling  for  some  time.  The  salt  has  been  used  instead  of  the 
"  dung-bath  "  in  dyeing.  . 

Orpiment  and  Realgar  have  been  described  on  pp.  207  and  212. 


WATER-GLASS 

The  substances  sold  under  this  name  are  silicates  of  sodium,  or 
potassium,  or  of  both.  They  are  soluble  in  water,  and  are  generally 
sold  as  thick,  sirupy  liquids. 

Commercial  water-glass  is  not  of  definite  composition,  but  is 
approximately  Na2Si409.  It  is  prepared  by  fusing  powdered  quartz, 
or  infusorial  earth,  with  caustic  soda  or  with  sodium  carbonate.  A 
small  quantity  of  charcoal  is  also  added,  to  assist  in  the  complete 
reduction  of  the  carbonate.  Sodium  sulphate  may  be  used  instead  of 
the  carbonate.  The  fusion  is  done  in  a  reverberatory  furnace,  and 
requires  8  or  10  hours.  Sometimes  ordinary  glass-pots  and  furnaces, 
p.  168,  are  used.  The  product  is  a  translucent  or  transparent  glass, 
slightly  green,  from  traces  of  iron.  It  is  powdered,  and  boiled  in 
water,  best  in  a  digester  under  pressure,  until  the  liquor  is  nearly 
neutral.  A  small  quantity  of  copper  or  lead  oxide  is  added,  to 
decompose  any  sodium  sulphide  formed  during  the  reduction. 
After  10  or  12  hours  the  solution  is  drawn  from  the  boiler,  filtered 
on  cloth,  and  allowed  to  settle.  It  is  then  concentrated  to  140°  Tw. 
(1.7  sp.  gr.).  The  material  used  must  be  pure,  and  especially  be 
free  from  lime,  alumina,  etc. 


PEROXIDES  231 

Water-glass  is  also  made  by  boiling  silica  in  a  digester  with  a 
solution  of  caustic  soda  for  a  long  time  at  60  pounds  pressure.  This 
yields  a  solution  of  the  silicate  directly,  which  needs  only  a  little 
concentrating.  Sometimes  gelatinous  precipitated  silica  is  dissolved 
in  caustic  soda,  and  the  solution  is  evaporated.  By  using  a  mixture 
of  equivalent  weights  of  sodium  and  potassium  carbonates,  a  more 
soluble  glass  is  produced,  which  is  sometimes  called  "  double  soluble 
glass." 

Potassium  silicate,  which  forms  a  more  soluble  glass  than  sodium 
silicate  does,  is  made  in  the  same  way. 

Water-glass  is  readily  decomposed  by  acids,  even  carbon  dioxide 
setting  free  silica,  and  forming  a  salt  of  the  alkali.  It  is  used 
extensively  as  an  addition  to  yellow  or  laundry  soaps ;  as  a  fixative 
for  pigments  in  calico  printing ;  as  a  vehicle  for  pigments  in  fresco 
painting ;  for  rendering  cloth  and  paper  draperies  non-inflammable  ; 
as  a  preservative  for  timber  and  porous  stone ;  in  the  manufacture  of 
artificial  stone ;  and  in  cement  mixtures  for  glass,  pottery,  wood,  and 
leather. 

PEROXIDES 

Barium  peroxide,*  Ba02,  is  made  by  calcining  barium  nitrate,  and 
heating  the  oxide  thus  obtained  in  an  atmosphere  of  dry,  pure  air. 
The  nitrate  is  packed  in  crucibles,  and  heated  in  a  furnace  at  880°  C. 
for  several  hours.  The  mass  fuses,  and  for  the  first  3  or  4  hours 
continues  to  evolve  nitrous  gases,  but  finally  becomes  solid,  though 
of  a  spongy,  porous  character.  This  is  barium  monoxide,  and  must 
be  carefully  protected  from  moisture  and  carbon  dioxide.  It  is 
broken  up  into  small  lumps,  and  put  into  flat  iron  trays,  which  are 
set  in  wide,  cast-iron  pipes,  through  which  a  current  of  air  can  be 
passed.  The  air  is  dried  thoroughly,  and  freed  from  carbon  dioxide 
before  it  enters  the  pipes,  by  passing  it  through  a  drying  tower,  or 
drum,  filled  with  caustic  soda  or  quicklime.  The  pipes  are  heate.d  to 
a  low  red  heat  (750°  C.),  and  the  air  passes  through  them.  The 
barium  oxide  takes  up  an  atom  of  oxygen,  forming  the  peroxide, 
while  nitrogen  escapes  from  the  pipe.  The  product  is  cooled  away 
from  contact  with  air. 

By  adding  an  excess  of  barium  hydroxide  solution  to  a  solution 
of  hydrogen  peroxide,  a  precipitate  of  hydrated  barium  peroxide, 
Ba02  •  8  H20  is  obtained,  which  is  stable.  By  drying  this  at  130°  C., 
all  the  water  is  expelled,  and  the  pure  peroxide  remains. 

*  J.  Soc.  Chem.  Ind.,  1890,  246.    L.  T.  Thome.    Chemiker-Zeitung,  1894,  68, 


232  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

Barium  peroxide  is  a  gray  or  white  powder,  insoluble  in  water, 
but  combining  with  it  to  form  a  hydrated  compound.  It  is  easily 
decomposed  by  dilute  acids,  and  even  takes  up  carbon  dioxide  from 
the  air.  Heated  to  a  bright  red  heat  (1000°  C.),  it  decomposes  into 
monoxide  and  free  oxygen.  Its  chief  uses  are  for  making  hydrogen 
peroxide,  and  in  the  preparation  of  oxygen  gas. 


Hydrogen  peroxide,*  H202,  is  made  by  decomposing  barium  perox- 
ide with  dilute  mineral  acids.  The  powdered  barium  peroxide 
is  "hydrated"  by  pouring  it  into  water,  and  stirring  for  about  3 
hours,  until  a  smooth  white  paste  is  formed.  This  is  added,  a  little 
at  a  time,  with  active  stirring,  to  the  dilute  acid,  contained  in  a  lead- 
lined  vessel.  The  temperature  during  decomposition  must  not  rise 
above  15°  C.,  and  the  vessel  is  cooled  with  ice-water.  The  precipi- 
tated barium  salt  is  allowed  to  settle,  and  the  clear  solution  of 
hydrogen  peroxide  is  decanted,  and  sometimes  filtered  rapidly  on 
cotton  cloth.  If  an  excess  of  barium  peroxide  is  used,  the  liquor  is 
alkaline,  and  will  not  keep.  In  this  case,  a  little  more  acid  is  added, 
and  prevents  decomposition.  The  commercial  strength  is  known  as 
a  10- volume  solution,  i.e.  3  per  cent  H202. 

By  using  hydrofluoric  acid,  the  precipitate  of  barium  fluoride 
may  be  readily  employed  to  generate  more  of  the  acid ;  if  nitric  acid 
is  used,  a  considerable  part  of  the  barium  is  recovered  as  barium 
nitrate,  with  which  more  barium  peroxide  can  be  made. 

Hydrogen  peroxide  is  a  powerful  oxidizing  agent  towards  sub- 
stances capable  of  oxidation,  but  with  bodies  which  give  off  oxygen 
readily  it  acts  as  a  reducing  agent,  giving  up  one  atom  of  oxygen  to 
unite  with  the  oxygen  from  the  body  in  question,  forming  a  molecule 
of  the  free  gas.  It  is  used  extensively  as  a  bleaching  agent,  espe- 
cially for  animal  fibres  and  tissues,  such  as  silk,  wool,  hair,  feathers, 
bone,  and  ivory.  It  has  long  been  used  as  a  hair  bleach  for  toilet 
use.  As  a  disinfectant  and  antiseptic,  it  finds  use  in  surgery ;  for 
restoring  the  colors  of  oil  paintings  which  have  darkened  with  age, 
it  is  very  effective,  if  the  paint  contains  lead ;  the  lead  sulphide  is 
oxidized  to  the  sulphate  by  the  peroxide,  the  black  color  of  the  for- 
mer being  destroyed.  Hydrogen  peroxide  has  also  been  proposed  as 
a  substitute  for  sodium  bisulphite  and  thiosulphate,  as  the  reducing 
material  for  chrome  tannage  processes ;  also  as  an  antichlor,  for  use 
after  chlorine  bleaching ;  and  as  a  general  antiseptic,  for  use  in  the 

*  Zeitschr.  f .  angew.  Chem.,  1890,  3.    G.  Lunge.    J.  Am.  Chem.  Soc.,  12,  64 
A.  Bourgougnon.    J.  Soc.  Chem.  Ind.,  1890.    Kingzett, 


OXYGEN  233 

fermentation  industries,  and  as  a  preservative  for  milk,  beer,  wine, 
and  other  fermentable  liquids. 


Sodium  peroxide,*  Na202,  has  recently  appeared  in  commerce  as  a 
bleaching  material.  The  technical  production  depends  upon  the  oxi- 
dation of  fused  metallic  sodium,  by  exposing  it  to  a  current  of  pure 
dry  air  or  oxygen.  The  sodium  is  contained  in  aluminum  trays, 
which  are  put  on  cars,  and  pushed  slowly  through  a  wide  iron  pipe, 
externally  heated  to  300°  C.,  while  air,  purified  as  described  on 
p.  231,  passes  through  the  pipe  in  the  opposite  direction.  The  tem- 
perature must  not  rise  above  300°  C.,  and  the  oxidation  must  be 
slow. 

Sodium  peroxide  is  a  yellowish  white,, very  hygroscopic  powder, 
which  is  chiefly  used  as  a  powerful  bleaching  agent.  It  gives  off  20 
per  cent  of  its  weight  as  active  oxygen,  t  It  dissolves  in  dilute  acids 
without  evolving  oxygen,  if  the  vessel  be  kept  cool,  yielding  a  strong 
solution  of  hydrogen  peroxide.  It  dissolves  in  water  with  the  loss 
of  some  oxygen,  and  a  great  evolution  of  heat,  which  may  be  suffi- 
cient to  set  fire  to  inflammable  bodies.  It  is  too  strongly  alkaline 
for  silk  or  wool  bleaching,  and  should  be  converted  into  magnesium 
peroxide  for  this  purpose.  This  is  easily  done  by  adding  magnesium 
sulphate  solution :  — 

Na202  +  MgS04  =  Na2S04  +  Mg02. 

The  solution  of  sodium  peroxide  attacks  cellulose,  and  produces 
an  effect  similar  to  that  obtained  by  "mercerizing"  with  caustic 
soda. 

OXYGEN 

Numerous  processes  have  been  devised  for  the  technical  produc- 
tion of  oxygen,  but  most  of  them  are  so  expensive,  or  require  such 
complicated  plants,  that  only  two  or  three  are  in  actual  operation  on 
a  large  scale  at  the  present  time. 

The  decomposition  of  potassium  chlorate  by  heating,  with  the 
addition  of  manganese  dioxide,  has  been  much  employed,  and  is  still 
the  favorite  laboratory  method  of  obtaining  a  pure  gas.  The  addi- 

*  J.  Soc.  Chem.  Ind.,  1892, 1004  (Patent  to  H.  Y.  Castner) ;  1893, 603.  Chemical 
Trade  Journal,  11,  208. 

t  Barium  peroxide  liberates  8  per  cent  of  its  weight  of  active  oxygen,  while  a 
12-volume  solution  of  hydrogen  peroxide  liberates  only  l£  per  cent  of  its  weight  of 
active  oxygen. 


234  OUTLINES   OF  INDUSTRIAL   CHEMISTRY 

tion  of  pyrolusite  lowers  the  temperature  of  the  decomposition,  and 
reduces  the  liability  of  explosion.  It  is  highly  important  that  the 
potassium  chlorate  and  pyrolusite  be  free  from  carbonaceous  matter. 
Deville's  process.  —  By  allowing  sulphuric  acid  to  drop  ;n  fine 
streams  on  red-hot  surfaces,  it  breaks  up  according  to  the  reaction:  — 

2  H2S04  =  2  S02  +  2  H20  +  02. 

In  order  to  separate  them,  the  gases  evolved  are  passed  though  cool- 
ing coils  to  condense  the  water,  and  then  through  scrubbers  contain- 
ing water,  to  remove  the  sulphur  dioxide.  The  retort  is  usually 
filled  with  broken  brick,  pumice,  or  other  porous,  acid-resisting 
material.  The  process  has  no  significance  as  a  method  of  prepar- 
ing oxygen  alone,  but  has  been  used  for  making  sulphuric  anhydride, 
SO3,  the  water  being  first^  condensed,  and  the  sulphur  dioxide  and 
oxygen  uniting  to  form  the  trioxide.  About  114  litres  of  oxygen  are 
obtained  from  1  kilo  of  sulphuric  acid  by  this  method. 

Boussingault's  process,  as  modified  by  Brin  brothers,  is  now 
worked  on  a  large  scale,  and  is  often  called  Erin's  process.*  Bous- 
singault  discovered  that  barium  peroxide  (Ba02),  when  heated  to  a 
high  temperature,  decomposes  into  the  monoxide  and  oxygen,  the 
latter  passing  off.  Then  by  heating  the  barium  oxide  to  a  low  red 
heat  in  a  current  of  air,  the  peroxide  can  be  regenerated.  But  his 
attempts  to  utilize  the  process  were  unsuccessful,  because  the  monox- 
ide soon  became  inert,  and  would  not  absorb  oxygen  from  the  air. 
This  was  due  to  the  fact  that  the  moisture  and  carbon  dioxide  in  the 
air  converted  the  barium  oxide  to  hydroxide  and  carbonate,  which 
are  very  stable  bodies,  even  at  high  temperatures,  consequently  the 
regeneration  of  peroxide  rapidly  decreased. 

As  modified  by  Brin  brothers,  the  temperature  of  the  retort 
remains  constant,  while  all  moisture  and  impurities  are  removed 
from  the  air.  Barium  oxide  is  made  from  barium  nitrate,  as  de- 
scribed on  p.  231 ,  and  put  into  vertical  retorts,  or  long  narrow  pipes, 
suspended  in  a  furnace  heated  by  producer  gas.  When  the  tempera- 
ture reaches  700°  C.,  purified  air  is  forced  into  the  retorts  under 
a  pressure  of  15  pounds  per  square  inch,  and  the  monoxide  takes  up 
an  atom  of  oxygen,  and  forms  the  peroxide.  The  air  supply  is  then 
cut  off,  and  the  pump  reversed,  so  as  to  form  a  vacuum  in  the  retort, 
reducing  the  pressure  to  about  26  to  28  inches  of  mercury.  Under 
these  conditions,  the  barium  peroxide  gives  off  an  atom  of  oxygen, 
and  is  reduced  to  the  monoxide.  The  gas  is  pumped  into  the  gas- 
ometer, and  when  it  ceases  to  be  evolved  the  pump  is  reversed  again, 

*  J.  Soc.  Chem.  Ind.,  1890,  246.    L.  T.  Thome.     1889,  82  and  517. 


OXYGEN 

and  air  forced  into  the  retort,  to  oxidize  the  monoxide  to  peroxide 
again. 

The  air  is  passed  through  purifiers,  one  filled  with  quicklime,  and 
the  other  with  caustic  soda ;  these  remove  the  water  and  carbon  di- 
oxide. By  the  alternate  use  of  pressure  and  vacuum,  the  temperature 
may  be  kept  constant  at  700°  C.  The  oxygen  obtained  is  about  96 
per  cent  pure.  The  baryta  is  removed  once  in  six  or  eight  months, 
and  broken  up  to  prevent  caking,  after  which  it  is  returned  to  the 
retort.  The  yield  of  oxygen  gas  at  each  operation  is  said  to  be 
about  10  litres  per  kilo  of  barium  oxide  employed.  The  cost  of  the 
gas  in  England  is  from  3s.  to  7s.  per  1000  cubic  feet. 

Tessie  du  Motay  process.*  —  This  depends  on  the  following  reac- 
tions :  — 

1)  2  Na2Mn04  +  2  H20  =  Mn203  +  4  NaOH  +  3  O. 

2)  Mn203  +  4  NaOH  +  30  (air)  =  2  Na2Mn04  +  2  H20. 

First,  sodium  manganate  is  prepared  by  mixing  a  manganese 
oxide  with  caustic  soda,  and  heating  with  free  access  of  air.  The 
following  reaction  takes  place  :  — 

2  Mn02  +  4  NaOH  +  O2  (air)  =  2  Na2Mn04  +  2  H20. 

The  sodium  manganate  thus  made  is  crushed,  and  mixed  to  a 
paste  with  caustic  soda  solution,  containing  from  5  to  10  per  cent 
NaOH.  This  is  dried  slowly  and  completely  in  shallow  pans,  and 
then  ignited  in  a  crucible  at  a  white  heat,  to  render  it  spongy.  But 
it  must  not  fuse.  This  yields  a  porous  manganate,  containing  an 
excess  of  caustic  soda,  which  is  filled  into  long  clay,  or  cast-iron 
retorts  of  peculiar  construction,!  set  at  an  incline  in  the  furnace, 
and  heated  to  a  regular  temperature  of  400°^50°  0.  Superheated 
steam  is  then  admitted  to  the  retort,  where  it  deoxidizes  the  man- 
ganate, regenerating  the  manganic  oxide  and  caustic  soda,  while 
oxygen  is  liberated,  and  is  cooled  and  collected  in  a  gasometer. 
Then  the  process  is  reversed,  and  purified  air,  which  has  passed 
through  a  heating  pipe,  set  in  the  furnace,  is  admitted  to  the  retort, 
where  it  oxidizes  the  material,  regenerating  the  sodium  manganate, 
while  pure  nitrogen  escapes.  The  cycle  of  operations  is  repeated 
indefinitely.  In  order  that  the  supply  of  oxygen  may  be  continuous, 
the  plant  is  usually  built  in  duplicate,  so  that  the  contents  of  one  set 
of  retorts  is  being  oxidized  with  air,  while  that  of  the  other  is  being 
deoxidized  with  steam. 

*  J.  Soc.  Chem.  Ind.,  1892,  312.     F.  Fanta. 
t  For  details,  see  J.  Soc.  Chem.  Ind.,  1892,  315. 


236  OUTLINES  OF  INDUSTRIAL   CHEMISTRY 

It  is  essential  that  the  sodium  manganate  be  granular,  and  that 
it  do  not  fuse  in  the  retort  j  also,  that  both  the  air  and  the  steam 
introduced  be  dry,  and  at  least  as  hot  as  the  contents  of  the  retort. 
An  excess  of  caustic  soda  seems  to  be  necessary,  to  render  the 
manganate  spongy  and  granular. 

This  process  is  complicated  in  it's  working  and  apparatus,  and  is 
apparently  not  so  economical  as  in  the  Brin  method. 

Linde  refrigeration  process.*  —  Refrigerating  machines,  depend- 
ing upon  the  expansion  of  compressed  air,  have  recently  been  brought 
to  a  high  state  of  perfection,  and  it  is  claimed  that  a  temperature  of 
—  200°  C.  can  be  secured  on  an  industrial  basis.  This  being  below 
the  critical  temperature  of  air,  the  latter  is  liquified.  By  allowing 
this  liquid  air  to  evaporate  at  the  ordinary  atmospheric  pressure, 
the  nitrogen  escapes  more  rapidly  than  the  oxygen,  and  a  residual 
gas  is  thus  obtained,  containing  over  70  per  cent  0.  This  is  concen- 
trated enough  for  many  purposes,  and  the  process,  which  is  entirely 
mechanical,  may  have  some  future  development. 

Methods  for  the  production  of  oxygen  by  the  electrolysis  of 
water  are  far  too  slow  and  expensive  for  industrial  use.  The  same 
is  probably  true  of  the  methods  depending  on  the  formation  of  cal- 
cium plumbate  (Ca2Pb04),  and  its  decomposition  into  calcium  car- 
bonate and  lead  peroxide  (Pb02),  from  which  oxygen  may  be 
obtained  :  — 

1)  2  CaC03  +  PbO  +  0  (air)  =  Ca2Pb04  +  2  C02. 

2)  Ca2Pb04  +  2  Na2C03  +  2  H20  =  4  NaOH  +  2  CaC03  +  Pb02. 

3)  2  CaC03  +  Pb02  «=  2  CaC03  +  PbO  +  O. 

The  uses  of  pure  oxygen  in  the  arts  are  not  very  numerous,  since, 
for  most  oxidizing  purposes,  air,  even  though  diluted  with  nitrogen, 
may  be  used.  It  is,  however,  employed  for  the  oxy-hydrogen  flame 
in  melting  platinum  and  other  refractory  metals,  and  for  soldering 
and  brazing ;  in  the  calcium  or  Drummond  light ;  for  the  purifica- 
tion of  illuminating  gas;  for  the  destruction  of  fusel  oil  in  high 
wines ;  and,  to  a  small  extent,  in  medicine,  and  in  the  manufacture 
of  sulphuric  anhydride.  Its  use  has  been  proposed  to  hasten  the 
melting  and  refining  of  glass ;  as  a  partial  substitute  for  air  in  blast 
furnace  running ;  for  the  oxidation  of  drying  oils  in  varnish  making ; 
and  to  assist  the  action  of  bleaching  powder  in  textile  bleaching. 

*  J.  Soc.  Chem.  Ind.,  1895,  984.  M.  Schroeter.  U.  S.  Consular  Reports,  54,  64. 
Chas.  de  Kay. 


SULPHATES  237 

REFERENCES 

Chemical  Trade  Journal,  1887,  145. 
Journal  of  the  Society  of  Chemical  Industry  :  — 
1885,  568.     W.  Smith. 

1889,  82,  517. 

1890,  246.     L.  T.  Thome. 
1892,  312.     F.  Fanta. 
1895,  984.     M.  Schroeter. 

Chemische  Industrie,  1890,  104,  120 ;  1891,  71.     G.  Kassner. 


SULPHATES 

/ 

The  sulphates  of  ammonium,  magnesium,  potassium,  and  sodium 
have  already  been  discussed  in  connection  with  the  industries  with 
which  they  are  most  nearly  related. 

Ferrous  sulphate,  green  vitriol,  or  copperas,  FeS04  -  7  H20,  is  a 
by-product  of  many  industries.  When  pyrites  is  distilled  for  sul- 
phur, the  residue,  consisting  of  ferrous  sulphide,  is  piled  upon 
inclined  tables  in  the  open  air,  and  allowed  to  weather,  water  being 
poured  over  the  heap  if  there  is  not  sufficient  rain.  Oxidation  takes 
place,  and  both  ferrous  and  ferric  sulphates  are  formed  in  the  mass. 
These  dissolve  in  the  water,  and  the  solution  of  mixed  sulphates 
flows  into  a  tank,  containing  some  sulphuric  acid  and  scrap  iron. 
The  reaction  between  the  acid  and  the  iron  reduces  the  ferric  salt, 
and  a  solution  of  ferrous  sulphate  is  obtained.  This  is  decanted 
from  the  sediment,  and  evaporated  until  saturated  in  lead  or  iron 
pans,  containing  scrap  iron.  It  is  then  allowed  to  settle,  and  the 
clear  green  solution  of  copperas  is  decanted  from  the  basic  ferric 
salt,  which  deposits  as  a  yellow  mud.  The  solution  is  cooled,  and 
light  green  crystals  of  ferrous  sulphate  (FeS04  •  7  H20)  separate, 
and  are  drained,  or  freed  from  mother-liquor  in  centrifugal  machines. 
The  mother-liquor  goes  back  to  the  neutralizing  tanks,  and  is  mixed 
with  fresh  liquor. 

Sometimes  pyrites  is  weathered  directly  for  copperas.  The  pro- 
cess is  carried  on  as  above  described,  except  that  the  free  sulphuric 
acid  formed  makes  the  addition  of  acid  to  the  liquor  unnecessary. 
The  receiving  tank  at  the  lower  end  of  the  oxidizing  tables  contains 
the  acid  liquor,  to  which  scrap  iron  is  added  to  reduce  the  ferric 
salt. 

FeS2  +  H20  +  7  0  =  FeS04  +  H2S04. 

A  large  amount  of  green  vitriol  is  obtained  as  a  by-product  in 
the  manufacture  of  aluminum  sulphate  from  shale  containing  pyrites 


238  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

(p.  245).  The  basic  ferric  sulphate  separated  is  reduced  by  treat- 
ment with  acid  and  scrap  iron. 

Wet  metallurgical  processes  for  the  production  of  cement  copper 
also  furnish  a  very  considerable  amount  of  copperas.  Copper  sul- 
phide ores,  low  in  copper,  are  exposed  in  heaps  to  the  weather  for 
several  months,  being  frequently  moistened  with  water.  By  oxida- 
tion of  the  sulphides,  copper  and  iron  sulphates  are  formed,  and  are 
leached  out  by  the  water.  These  liquors  are  run  into  tanks  contain- 
ing scrap  iron,  which  precipitates  the  copper,  and  also  reduces  the 
ferric  sulphate  to  the  ferrous  state.  The  solution  of  copperas  is 
clarified,  and  evaporated  to  crystallize. 

In  this  country,  the  "  sludge  acid  "  of  petroleum  refining  is  often 
diluted,  and  used  to  make  ferrous  sulphate,  by  dissolving  scrap  iron 
in  it.  The  acid  "pickling  liquors,"  used  in  foundries  and  wire 
mills  for  cleaning  the  surfaces  of  castings  and  wire,  are  treated  with 
scrap  iron  to  neutralize  free  acid,  and  the  solution  then  evaporated 
for  copperas. 

All  processes  for  making  ferrous  sulphate  yield  dilute  solutions, 
which  are  best  evaporated  by  direct  application  of  heat  to  the  sur- 
face of  the  liquid  (see  &,  p.  4),  thus  preventing  oxidation.  After 
clarification,  the  liquid  is  put  into  large  lead-lined  tanks,  in  which 
strings  or  wooden  rods  are  suspended;  on  these  the  large  bluish 
green  crystals  of  ferrous  sulphate  form. 

The  crystals  contain  7  molecules  of  crystal  water ;  when  heated 
to  140°  C.,  6  molecules  of  water  are  expelled,  but  the  last  molecule  is 
not  removed  until  the  temperature  reaches  260°  C. ;  at  this  temper- 
ature, some  of  the  acid  begins  to  escape,  and  the  formation  of  the 
basic  salt  begins.  At  a  red  heat,  sulphuric  anhydride  is  given  off, 
and  ferric  oxide  is  left. 

The  crystals  of  ferrous  sulphate  effloresce  quickly  when  exposed 
to  the  air,  their  surfaces  becoming  coated  with  a  brownish  white 
powder  of  basic  ferric  sulphate,  formed  by  oxidation.  Ultimately, 
the  entire  crystal  is  converted  to  this  basic  salt.  By  adding  alcohol 
to  a  ferrous  sulphate  solution,  the  salt  is  precipitated  in  fine  crys- 
tals, which  are  much  more  stable  in  the  air  than  are  the  ordinary 
kind. 

Copperas  solution  oxidizes  quickly  in  the  air,  and  a  yellow  pre- 
cipitate of  basic  ferric  sulphate  separates.  Commercial  green  vitriol 
very  often  contains  copper  sulphate,  and  sometimes  nickel  sulphate. 
When  very  large  quantities  of  these  impurities  are  present,  the  color 
is  very  dark,  and  the  salt  is  called  "  black  vitriol." 

Ferrous  sulphate  is  largely  used  as  a  mordant  in  dyeing ;  in  the 


SULPHATES  239 

preparation  of  fuming  sulphuric  acid ;  for  disinfecting  purposes ;  in 
the  manufacture  of  ink,  Prussian  blue,  and  various  pigments ;  and 
for  precipitating  gold  from  solution  in  metallurgical  processes. 

Copper  sulphate,  blue  vitriol,  or  "bluestone."  CuS04  -  5  H20,  is 
now  largely  obtained  as  a  by-product  in  the  "  parting  "  of  gold  and 
silver  with  sulphuric  acid.  The  gold  and  silver  alloy  is  boiled  with 
concentrated  sulphuric  acid  in  cast-iron  pans;  the  silver  is  dissolved, 
the  solution  separated  from  the  residue  of  gold,  and  the  silver  sul- 
phate decomposed  with  metallic  copper.  Metallic  silver  precipi- 
tates, and  copper  sulphate  remains  in  solution. 

Copper  sulphate  is  also  prepared  by  allowing  sulphuric  acid  to 
drip  on  scrap  copper  with  free  access  of  air,  the  copper  being  slowly 
oxidized  and  dissolved.  Or  metallic  copper,  contained  in  lead-lined 
tanks,  may  be  treated  with  hot  acid.  Scrap  copper  is  often  heated 
red-hot  in  a  furnace,  and  then  sulphur  is  thrown  in,  and  the  door 
tightly  closed.  Cuprous  sulphide  is  formed,  which  is  then  oxidized 
at  a  red  heat  by  admitting  air  into  the  furnace.  A  mixture  of  cop- 
per sulphate  and  oxide  is  thus  produced,  which  is  treated  with  hot 
dilute  sulphuric  acid,  and  the  solution  so  obtained  is  evaporated. 

1)  2Cu  +  S  =  Cu2S. 

2)  Cu2S  +  5  O  =  CuS04  +  CuO. 

3)  (CuS04  +  CuO)  +  H2S04  =  2  CuS04  +  H20. 

Copper  sulphide  ores,  chalcopyrite,  and  chalcocite,  and  artificial 
copper  mattes,  are  sometimes  converted  into  blue  vitriol;  but  the 
ferrous  sulphate  formed  crystallizes  with  the  copper, sulphate.  Such 
blue  vitriol  is  much  used  where  iron  is  not  injurious.  The  iron  may 
be  removed  by  roasting  the  salt  until  the  ferrous  sulphate  is  decom- 
posed into  oxide,  and  then  dissolving  in  water  and  recrystallizing. 
Or  the  solution  may  be  boiled  with  a  little  nitric  acid,  or  lead  perox- 
ide, until  the  iron  is  converted  to  the  ferric  state,  when,  by  adding 
copper  carbonate,  or  oxide,  or  barium  carbonate,  and  boiling  again, 
the  iron  precipitates. 

Some  copper  ores  contain  zinc,  and  yield  a  bluestone,  contami- 
nated with  zinc  sulphate.  The  acid  "  dipping  liquors "  from  copper 
and  brass  works  are  also  used  for  blue  vitriol,  but  these  are  gener- 
ally contaminated  with  zinc.  The  hammer-scales  (copper  oxide)  pro- 
duced in  rolling  and  working  sheet  copper,  are  often  dissolved  in 
dilute  acid  to  form  blue  vitriol. 

Copper  sulphate  forms  deep  blue  crystals,  containing  5  molecules 
of  water.  In  dry  air,  the  crystals  effloresce,  and  fall  to  a  white 


240  OUTLINES  OF  INDUSTRIAL   CHEMISTRY 

powder,  but  all  the  water  does  not  escape  until  the  mass  is  heated  to 
240°  C.  The  anhydrous  salt  is  a  white  powder,  and  will  abstract 
water  from  alcohol  or  organic  liquids.  Bluestone  is  largely  used  as 
a  mordant  in  calico  printing,  and  in  dyeing;  for  preparing  other 
copper  salts  and  pigments;  in  the  preparation  of  germicides  and 
insecticides  (Bordeaux  mixture,  etc.),  for  batteries,  and  electrolytic 
baths ;  in  metallurgy,  and  in  most  operations  where  a  soluble  copper 
salt  is  desired. 


Zinc  sulphate  or  white  vitriol,  ZnS04  •  7  H20,  is  not  of  very  great 
importance.  It  is  made  by  roasting  zinc  blende  (sphalerite),  or 
zinc-lead  ores,*  and  leaching  the  mass  with  water  or  dilute  sulphuric 
acid.  Or  scrap  zinc  is  dissolved  in  dilute  acid.  The  solution  may 
be  purified  from  copper  by  introducing  a  plate  of  metallic  zinc,  upon 
which  the  copper  deposits.  Iron  is  removed  by  heating  the  solu- 
tion in  the  air  for  a  considerable  time,  while  stirring  well,  and  then 
adding  a  small  amount  of  zinc  carbonate  or  oxide,  to  precipitate  the 
ferric  oxide. 

Zinc  sulphate  forms  colorless  crystals  containing  7  molecules  of 
water,  which  effloresce  in  the  air.  It  is  very  soluble  in  water. 
When  heated,  the  crystals  melt  in  their  water  of  crystallization,  and 
at  100°  C.,  6  molecules  of  water  are  expelled.  The  final  molecule  is 
driven  off  at  300°  C.,  while  at  a  red  heat,  the  anhydrous  salt  decom- 
poses, leaving  a  residue  of  zinc  oxide. 

Zinc  sulphate  is  used  somewhat  in  dyeing  and  printing;  as  a 
disinfectant ;  for  preserving  and  clarifying  glue  solutions ;  in  medi- 
cine as  an  astringent,  and  in  lotions ;  in  the  preparation  of  dryers 
for  "  boiled  oils " ;  and  to  some  extent,  as  a  preservative  for  hides 
and  timber. 


Aluminum  sulphate,  Al2(S04)g,  18H20,  is  now,  extensively  em- 
ployed in  the  arts,  under  the  name  "concentrated  alum."  It  is 
usually  prepared  from  pure  kaolin,  or  from  bauxite  [A120(OH)4, 
or  A1203'2H20],  or  from  the  hydrated  alumina  obtained  in  the 
cryolite  soda  process  (p.  92).  Aluminum  hydroxide,  prepared  from 
bauxite  or  cryolite,  is  almost  entirely  free  from  iron,  since  it  is 
precipitated  from  an  alkaline  solution  of  sodium  aluminate,  in  which 
the  iron  of  the  mineral  is  not  soluble.  When  this  hydroxide  is 
dissolved  in  pure  sulphuric  acid,  a  very  pure  aluminum  sulphate 
is  formed. 

*  Bruno  Kerl,  Mineral  Industry,  1895,  83. 


SULPHATES  241 

(a).  Aluminum  sulphate  from  clay :  — China  clay,  free  from  cal- 
cium carbonate,  is  calcined  at  a  moderate  heat,  until  nearly  all  of  its 
water  is  expelled ;  then  it  is  powdered  and  sifted  through  very  fine 
sieves,  and  mixed  with  a  little  less  than  the  theoretical  quantity  of 
sulphuric  acid  of  1.45  to  1.50  sp.  gr.,  and  heated  with  free  steam  to 
start  the  reaction,  which  soon  becomes  very  violent.  The  mass 
swells,  and  quantities  of  steam  escape,  but  when  the  reaction  ceases, 
the  swelling  subsides.  If  it  is  now  allowed  to  cool,  a  stone-like 
substance  is  obtained,  which  is  much  employed  in  the  arts  as  "  alum 
cake."  It  contains  all  the  silica  and  iron  impurities  of  the  clay, 
and  usually  from  2  to  3  per  cent  of  free  acid.  But  if  the  thick  pasty 
mass  is  diluted  with  warm  water  while  still  hot,  and  decanted  or 
filtered  from  the  insoluble  impurity,  a  solution  of  the  sulphate  is 
obtained,  which  on  evaporation  yields  a  salt  containing  about  0.2 
per  cent  iron,  and  a  trace  of  free  acid.  It  is  often  customary  to 
convert  this  solution  directly  into  alum  (p.  244),  by  adding  the 
necessary  alkaline  sulphate. 

(b).  Aluminum  sulphate  from  bauxite :  —  Bauxite  is  more  easily 
decomposed  by  acid  than  is  clay,  but  if  dissolved  directly,  the  prod- 
uct contains  a  large  amount  of  iron.  However,  considerable  bauxite 
is  decomposed  with  acid  to  form  a  hard  cake  which  is  known  in 
trade  as  "  alumino-ferric  cake,"  and  is  used  for  many  purposes 
where  iron  and  free  acid  do  no  harm,  and  a  cheap  source  of  soluble 
alumina  is  desired;  e.g.  in  precipitating  sewage  and  waste  liquors 
from  dyeworks. 

But  a  pure  sulphate  is  obtained  by  the  following  processes : 
The  bauxite  is  roasted  and  powdered  very  fine,  and  is  mixed  with 
calcined  and  very  finely  powdered  soda-ash,  in  the  proportion  of  1 
molecule  of  A1203  to  1.1  molecules  of  Na2O.  If  the  bauxite  contains 
much  silica,  more  soda  may  be  used,  but  the  amount  should  not  be 
sufficient  to  leave  free  carbonate  in  the  product  after  calcination, 
otherwise  the  mass  may  fuse,  and  the  solution  of  sodium  aluminate 
obtained  by  lixiviating  will  be  unstable.  The  mixture  is  calcined 
at  a  white  heat,  until  all  carbon  dioxide  and  water  are  expelled; 
this  requires  3  or  4  hours.  The  product  is  a  porous,  pale  green  or 
blue  mass,  which  is  ground  and  lixiviated  with  hot  water,  in  a 
wooden  tank,  while  stirring  actively.  A  little  caustic  soda  is  added 
to  the  water,  to  prevent  precipitation  of  alumina.  (See  Bayer's 
process,  below.)  The  lixiviation  must  be  rapid,  not  occupying  more 
than  10  minutes,  after  which  the  solution  of  aluminate  is  decanted. 
According  to  Jurisch,*  the  liquor  should  be  at  least  35°  Be.  density, 

*  Fabrikation  von  Schwefelsaure  Thonerde,  52. 


242  OUTLINES  OF  INDUSTRIAL   CHEMISTRY 

and  contain  170  grams  A1203,  and  182  grams  JSTa20,  per  litre.  Weaker 
solutions  are  said  to  yield  a  slimy  precipitate  of  alumina,  when 
decomposed  in  the  next  stage  of  the  process.  The  liquor  is  quickly 
filtered  (a  filter  press  is  recommended),  heated  to  90°  C.,  and  de- 
composed by  passing  carbon  dioxide  into  it,  by  which  hydrated 
alumina  is  precipitated  in  a  granular  form,  which  is  readily  washed 
free  from  soda.  The  silica  and  iron  remain  dissolved  in  the  mother- 
liquor.  The  carbon  dioxide  may  be  derived  from  limekiln  gases, 
or  from  the  calcination  of  sodium  bicarbonate. 

The  pure  aluminum  hydroxide  thus  prepared  is  added  slowly  to 
hot,  pure,  concentrated  sulphuric  acid,  until  the  frothing  ceases ; 
the  solution  is  run  into  flat  lead  pans  to  cool,  when  it  forms  a  crys- 
talline mass.  If  an  excess  of  alumina  is  used  in  neutralizing  the 
acid,  basic  salts  result. 

The  sulphate  made  in  this  way  is  nearly  free  from  iron  and 
silica,  but  sometimes  contains  small  quantities  of  soda.  It  is  now 
much  used  in  the  arts  under  the  name  of  "concentrated  alum." 
From  analysis,  the  formula  appears  to  be,  A12(S04)3  •  20  H20,  but 
the  slight  excess  of  water  may  be  hygroscopic,  and  not  combined. 

According  to  the  patented  process  of  K.  J.  Bayer,*  a  solution  of 
sodium  aluininate  is  prepared,  containing  1  A1203  to  1.8  Na20 ;  by 
stirring  more  powdered  alumina  into  this,  a  crystalline  precipitate 
of  aluminum  hydroxide  separates,  until  the  solution  contains  the 
molecular  proportions,  1  A1203  to  6  Na2O,  silica  and  other  impurities 
remaining  in  solution.  When  evaporated  to  a  density  of  40°  Be.,  and 
digested  with  finely  powdered  bauxite,  at  170°  C.,  under  pressure  of 
4  atmospheres,  while  stirring  actively,  the  solution  dissolves  more 
alumina  out  of  the  bauxite,  to  again  form  sodium  aluminate  liquor, 
having  the  molecular  proportion  of  about  1  A1203  to  1.8  Na20.  This 
solution  is  decomposed  as  above,  and  the  cycle  of  operations  re- 
peated. The  silica  dissolved  in  the  aluminate  solution  is  precipi- 
tated during  the  digestion  as  an  insoluble  double  silicate  of  sodium 
and  aluminum  (Na2Al2Si3010  +  9  H20),  and  remains  with  the  resi- 
due, together  with  the  iron.  The  hydrated  alumina  precipitated  is 
washed  free  from  sodium  salts,  and  dissolved  in  acid  as  already 
described. 

Another  process  for  sulphate  consists  in  dissolving  bauxite  in 
dilute  acid,  at  a  temperature  of  90°  C.,  with  the  addition  of  a  little 
sodium  nitrate  to  oxidize  all  the  iron  to  the  ferric  state ;  then  more 
bauxite,  together  with  a  little  potash  alum,  is  added.  After  stirring 

*  Jurisch,  Fabrikation  von  Schwefelsaure  Thonerde,  17-18.  German  patents, 
43,977  (1887)  and  65,604  (1892).  J.  Soc.  of  Cliem.  Ind.,  1888,  625. 


SULPHATES  243 

thoroughly,  the  whole  is  left  for  several  weeks.  The  iron  combines 
with  some  of  the  alumina  to  form  a  precipitate, 

2Al2(S04)3  +  2Fe(OH)3. 

(c).  Sulphate  from  cryolite : — The  hydrated  alumina  obtained 
in  the  cryolite  soda  process  (p.  92)  may  be  dissolved  to  make 
aluminum  sulphate  in  the  usual  way.  The  product  may  contain 
some  soda. 

Another  method  of  utilizing  cryolite  depends  on  the  following 
reactions :  — 

1)  6  NaF,  2  A1F3  +  6  Ca(OH)2  =  6  CaF2  +  2  Al(NaO)3  +  6  H2O. 

2)  2  Al(NaO)3  +  6  NaF,  2  A1F3  =  2  A1203  + 12  NaF. 

3)  Al  A  +  3  H2S04  =  A12(S04)3  +  3H20. 

Powdered  cryolite  is  boiled  with  milk  of  lime,  and  the  solution 
of  sodium  aluminate  decanted.  By  boiling  the  aluminate  liquor  for 
a  long  time,  with  more  powdered  cryolite,  while  stirring  thoroughly, 
the  second  reaction  takes  place ;  the  residue  is  chiefly  hydrated 
aluminum  oxide,  while  sodium  fluoride  goes  into  solution.  By  boil- 
ing the  latter  with  milk  of  lime,  caustic  soda  may  be  obtained  as  a 
by-product. 

2  NaF  +  Ca(OH)2  =  CaF2  +  2  NaOH. 

By  evaporating  an  aluminum  sulphate  solution  until  very  con- 
centrated, and  then  cooling,  a  solid  cake  of  the  salt  having  a  crystal- 
line structure  is  obtained ;  its  composition  corresponds  to 

A12(S04)3.20H20. 

It  is  difficult  to  obtain  single  crystals,  but  the  usual  formula  assigned 
to  them  is  A12(S04)3  •  18  H20.  The  commercial  product,  however, 
never  corresponds  exactly  to  this  formula.  As  now  prepared,  it 
contains  but  little  free  acid,  or  excess  of  alumina  (basic  salt),  and 
only  a  minute  trace  of  iron.  It  should  contain  14  to  14.5  per  cent 
A1203,  and  dissolve  readily  in  water  to  form  a  clear  solution;  i.e.  no 
basic  salt  should  be  present.  About  0.5  per  cent  free  acid,  and  0.01 
to  0.1  per  cent  Fe203,  are  the  average  content  of  commercial  sam- 
ples. Since  it  may  now  be  had  of  great  purity,  aluminum  sulphate 
has  largely  replaced  alum  in  the  arts.  It  is  extensively  used  as  a 
mordant  in  dyeing ;  in  preparing  size  for  paper ;  for  making  alum 
and  aluminum  salts  (red  liquor,  etc.) ;  in  tawing  skins ;  for  pre- 
cipitating sewage  or  coloring  matter  from  water;  and,  in  general, 
for  all  purposes  where  alum  was  formerly  used. 


244  OUTLINES  OF  INDUSTRIAL   CHEMISTRY 

ALUM 

An  alum  is  a  double  sulphate  of  a  univalent  alkali  metal  and  a 
hexad  metallic  radical  of  the  form  (E2)=,  crystallized  with  24  mole- 
cules of  water.  The  general  formula  is  therefore 

M2S04',R2(S04)3.24H20, 

or,  as  it  is  more  frequently  written,  MR(S04)4  •  12  H20.  The  alkali 
metal  may  be  sodium,  potassium,  ammonium,  lithium,  caesium,  or 
rubidium.  The  hexad  radical  contains  aluminum,  chromium,  iron,  or 
manganese.  In  the  vast  majority  of  alums,  the  essential  part  is  alu- 
minum sulphate,  but  since  this  does  not  crystallize  well  alone,  it  has, 
until  recently,  been  difficult  to  obtain  it  pure  enough  for  most  pur- 
poses. But  the  addition  of  an  alkali  sulphate  forms  alum,  which 
crystallizes  beautifully  and  is  very  pure,  while  the  alkali  sulphate 
itself  has  no  injurious  action  in  most  cases  where  aluminum  sul- 
phate is  used.  But  since  "concentrated  alum'7  (p.  240)  can  now 
be  had  very  pure,  it  is  generally  preferred,  because  of  its  greater 
strength  and  solubility. 

All  alums  crystallize,  with  the  same  number  of  molecules  of 
water,  in  the  regular  system,  either  as  octahedrons,  or  as  cubes. 
They  are  all  isomorphous,  and  a  crystal  of  one  kind  of  alum  will 
continue  to  grow  by  accretion,  if  placed  in  a  solution  of  another 
alum.  Alum  crystallizes  from  solution  very  perfectly,  and  forms 
exceedingly  pure  crystals,  even  from  impure  solutions ;  it  is  because 
of  this  property  that  it  finds  such  extended  use  in  the  arts. 

Alum  occurs  in  nature  in  small  quantities,  produced  by  the 
action  of  volcanic  gases  on  rocks  consisting  of  potash-aluminum 
silicates;  also  in  combination  with  iron  and  aluminum  hydroxides 
in  the  mineral  alunite,  or  alum  stone,  K2S04,  A12(S04)3,  4  A1(OH)3, 
also  formed  by  volcanic  action.  Other  sources  are  alum  slates  and 
shales,  clay,  bauxite,  and  cryolite. 

Alunite,  or  alum  stone,  is  insoluble  in  water.  It  is  calcined  in 
heaps,  or  in  small  shaft  kilns,  at  about  500°  C.,  and  the  mass  is  then 
exposed  to  the  weather  for  several  months,  being  moistened  from 
time  to  time.  The  calcination  converts  the  iron  and  aluminum 
hydroxide  into  insoluble  oxides,  and  the  weathering  forms  alum  in 
the  mass,  which  is  dissolved  by  lixiviation,  and  recrystallized.  The 
alum  thus  obtained  is  basic,  and  crystallizes  in  cubes ;  owing  to 
imperfect  settling  of  the  liquors  before  crystallization,  some  iron 
oxide  is  inclosed,  giving  the  crystals  a  red  color.  This  iron  is,  how- 
ever, quite  insoluble,  and,  no  free  acid  being  present,  the  alum  yields 


ALUM  245 

a  very  pure,  neutral  solution,  and  is  especially  desired  for  many 
purposes.  It  is  most  extensively  made  at  Tolfa,  near  Rome,  and 
so  is  called  Roman  alum.  An  imitation  is  made  by  coloring  alum 
crystals  derived  in  other  ways,  with,  brick  dust,  or  with  iron  oxide 
(Venetian  red). 

Alum  slates  or  shales  are  mixtures  of  iron  pyrites,  aluminum 
silicates,  and  bituminous  matter.  By  exposure  to  the  weather,  the 
pyrites  is  oxidized  to  ferrous  sulphate  and  sulphuric  acid,  and  these 
react  with  the  aluminum  silicate  to  form  aluminum  sulphate.  Basic 
ferric  sulphate  is  also  formed.  The  oxidation  can  be  greatly  has- 
tened by  roasting  the  shale  before  weathering  it,  but  the  temperature 
must  not  be  high  enough  to  drive  off  the  sulphur.  After  weathering, 
the  mass  is  systematically  lixiviated,  and  a  solution  of  aluminum 
sulphate,  having  a  specific  gravity  of  about  1.16,  and  containing  some 
calcium  and  iron  sulphates,  comes  from  the  leach  tanks.  This  is 
clarified  by  settling,  and  some  of  the  calcium  and  basic  ferric  sul- 
phates deposit.  The  solution  is  evaporated  in  lead  or  iron  pans  by 
surface  heating  with  direct  flame,  until  ferrous  sulphate  crystallizes 
on  cooling,  and  then  the  mother-liquor  containing  the  aluminum  sul- 
phate is  further  concentrated  to  1.40  sp.  gr.  During  this  evapora- 
tion, more  calcium  sulphate  and  a  basic  ferric  sulphate  separate. 
Scrap  iron  is  generally  placed  in  the  vessel  during  concentration, 
to  convert  the  ferric  sulphate  into  the  basic  salt,  and  to  reduce  the 
destructive  action  on  the  pan.  The  hot  solution  is  decanted  from 
the  sediment,  and  mixed  with  potassium  or  ammonium  sulphate  in 
exact  amount  to  form  the  alum.  By  agitating  the  liquid  during  the 
cooling,  very  fine  crystals  of  alum,  called  "  alum  meal,"  separate. 

If  the  aluminum  sulphate  solution  contains  much  iron,  as  is  gen- 
erally the  case  when  working  on  a  large  scale,  it  is  often  the  prac- 
tice to  add  potassium  chloride  to  form  the  alum.  By  decomposing 
the  iron  sulphates,  this  forms  potassium  sulphate  in  the  solution, 
and,  at  the  same  time,  converts  the  iron  into  the  very  soluble  ferric 
and  ferrous  chlorides,  which  remain  in  the  solution  when  the  alum 
separates.  But  with  a  pure  solution  of  aluminum  sulphate,  this 
causes  loss  by  converting  part  of  the  aluminum  into  the  very  soluble 
aluminum  chloride :  — 

4  A12(S04)3  +  6  KC1  =  3  SK2S04,  A12(S04)3|  +  2  A1C13. 

The  alum  meal  is  washed  with  cold  water  in  a  centrifugal 
machine,  and  recrystallized.  It  is  sold  both  in  the  crystallized 
and  in  the  powdered  form. 

The  manufacture  of   alum  from   clay,  bauxite,  or   cryolite  in- 


246  OUTLINES   OF  INDUSTRIAL   CHEMISTRY 

volves  the  preparation  of  a  pure  solution  of  aluminum  sulphate  by 
methods  already  given,  and  the  addition  of  the  exact  quantity  of 
alkali  sulphate  to  form  the  alum. 

Blast  furnace  slag  has  been  proposed  as  a  source  of  alum.  It  is 
decomposed  with  hydrochloric  acid,  and  the  aluminum  chloride  solu- 
tion is  decomposed  with  calcium  carbonate ;  the  aluminum  hydroxide 
so  obtained  is  dissolved  in  sulphuric  acid.  The  process  is  not  suc- 
cessful, however. 

"Neutral  alum"  is  made  by  adding  sodium  or  potassium  carbon- 
ate, or  caustic  soda  to  an  alum  solution,  until  a  slight  precipitate 
remains,  even  after  vigorous  agitation.  After  filtering,  cubical  crys- 
tals of  the  neutral  alum  can  be  obtained,  but,  as  a  rule,  the  neutral 
solution  is  made  by  the  user,  and  is  not  crystallized.  Neutral  alum 
is  much  used  in  mordanting,  because  of  the  great  readiness  with 
which  it  deposits  alumina  on  the  fibre. 

The  most  important  alums  of  commerce  are  potassium  alum, 
K2S04  •  A12(S04)3  •  24  H20,  and  ammonium  alum, 

(NH4)2S04  -  A12(S04)3.  24  H20. 

The  latter  is  less  soluble  than  the  potash  salt,  but  in  all  other  re- 
spects they  are  quite  similar.  Both  are  stable  in  the  air. 

Sodium  alum,  Na2S04  -  A12(S04)3  •  24  H20,  is  very  soluble  in  water, 
and  difficult  to  purify.  Moreover,  the  crystals  effloresce  on  exposure 
to  the  air;  in  this  condition,  they  are  sometimes  sold  as  "porous 
alum." 

When  heated,  alum  loses  water  and  some  sulphuric  acid,  and 
falls  to  a  white  powder,  "  burnt  alum,"  which  is  difficultly  soluble  in 
water.  This  is  used  occasionally  as  a  caustic  in  medicine. 

The  chief  uses  of  common  alum  are  as  a  mordant  in  dyeing;  m 
preparing  size  for  paper-making ;  in  tawing  skms ;  in  making  pig- 
ment lakes ;  for  clarifying  turbid  liquids,  and  precipitating  sewage ; 
and  for  hardening  plaster  of  Paris  casts,  and  other  articles. 

Besides  the  common  alums  of  trade,  containing  aluminum  sul- 
phate as  a  basis,  two  others,  iron  alum  and  chrome  alum,  are  also 
employed  in  the  arts  to  some  extent. 

Iron  alum,  which  may  be  either  (NH4)2S04,  Fe2(S04)3  •  24  H20,  or 
K2S04,  Fe2(S04)3  •  24  H20,  is  made  by  oxidizing  a  copperas  solution 
to  form  ferric  sulphate,  adding  the  proper  quantity  of  alkali  sul- 
phate, and  cooling  below  10°  C.  It  forms  pale  violet  crystals,  which 
are  rather  unstable,  efflorescing  and  oxidizing  in  the  air,  forming 
basic  ferric  salt.  Iron  alum  is  chiefly  used  as  a  mordant. 

Chrome  alum,  K^SO^  Cr2(S04)3  •  24  H20,  is  largely  produced  as  a 


CYANIDES  247 

by-product  in  the  manufacture  of  alizarine.  A  mixture  of  potassium 
bichromate  and  sulphuric  acid  is  employed  to  oxidize  anthracene 
(Ci4H10)  to  anthraquinone  (C14H802),  from  which  the  alizarine  is  pro- 
duced. The  effect  of  the  reducing  action  of  the  organic  body  on  the 
bichromate  mixture  is  to  form  potassium  and  chromium  sulphates  in 
the  solution  in  proper  proportion  to  unite  in  chrome  alum :  — 

C14H10  +  K2Cr207  +  4  H2S04  =  C14H8O2  +  KJSO*  Cr2(SO4)3  +  5  H20. 

Chrome  alum  forms  deep  violet  crystals,  which  effloresce  on 
exposure  to  the  air.  It  is  used  as  a  mordant ;  and  in  tawing  skins, 
especially  in  certain  chrome  tannage  processes. 

REFERENCES 

Die  Fabrikation  des  Alauns,  des  Bleiweisses  und  des  Bleizuckers.     Dr.  F.  Jiine- 

mann,  Leipzig,  1882.     (Hartleben.) 
Die  Fabrikation  von  schwefelsaurer  Thonerde.     K.  W.  Jurisch,  Berlin,  1894. 

(Fischer. ) 
Journal  of  the  Society  of  Chemical  Industry :  — 

1882,  124.     B.  E.  R.  Newlands. 

1883,  482.     J.  W.  Kynaston. 
1886,  16.     J.  W.  Beveridge. 

1888,  625.     (Bayer's  Patent  for  Alumina  Hydrate.) 
1892,  4  and  321. 
Chemical  News,  42,  191  and  202. 


CYANIDES 

Cyanides  are  now  produced  from  the  spent  iron  oxide  from  gas 
purification,  and  from  fusions  of  alkaline  carbonates  with  nitroge- 
nous organic  matter  and  iron  borings.  A  small  quantity  of  ammo- 
nium sulphocyanide  (thiocyanate)  is  made  synthetically,  but  the 
manufacture  of  cyanides  directly  from  the  nitrogen  of  the  air  has 
not  yet  been  put  on  a  commercial  basis.  Bunsen  and  Playfair's 
process  for  making  cyanides,  by  heating  barium  carbonate  with 
powdered  charcoal  in  an  atmosphere  of  dry  nitrogen,  cannot  be 
worked  successfully  on  a  large  scale.  It  depends  on  the  following 
reaction :  — 

BaC03  +  4  C  +  2  N  =  Ba(CISr)2  +  3  CO. 

A  large  amount  of  cyanogen  compounds  are  present  in  the  gases 
from  iron  blast  furnaces,  and  much  ingenuity  has  been  expended  on 
methods  for  recovering  these  salts,  but  as  yet  with  little  success. 
Practically,  all  cyanogen  derivatives  are  now  made  from  either 
ammonium  sulphocyanide  or  alkali  ferrocyanides. 


248  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

Ammonium  sulphocyanide  (thiocyanate),  NH4SCN,  is  sometimes 
prepared  by  Tscherniak  and  Giinzburg's  modification  of  Gelis'  pro- 
cess.* This  depends  on  the  following  reactions  :  — 

1)  CS24-2NH3  =  NH4S2CNH2.     (Ammonium  dithiocarbamate.) 

2)  NH4S2CNH2  =  NH4SCN  +  H2S. 

Carbon  disulphide  and  ammonium  hydroxide  (0.91  sp.  gr.),  in 
proper  proportion  for  reaction  (1),  are  heated  in  an  autoclave  to 
125°  C.,  while  stirring  actively.  The  steam  is  then  cut  off,  but  the 
stirring  continued  until  the  pressure  rises  to  15  atmospheres.  This 
completes  the  first  reaction,  and  the  contents  of  the  autoclave  are 
blown  off  into  a  still,  which  is  heated  to  110°  C.,  at  which  point  the 
ammonium  dithiocarbamate  is  decomposed.  The  products  of  distil- 
lation are  passed  through  condensers  and  scrubbers  to  collect  vola- 
tile ammonium  salts  and  carbon  disulphide,  while  the  hydrogen 
sulphide  is  conducted  into  a  gasometer.  The  liquid  in  the  still 
contains  ammonium  sulphocyanide,  and  is  evaporated  in  tin  vessels, 
and  crystallized. 

Sometimes  lime  and  manganese  peroxide  are  added  to  assist  the 
reaction  in  the  autoclave,  in  which  case  calcium  sulphocyanide  is 
formed :  — 

2  CS2  +  2  NH3  -f  Mn02  +  CaO  =  Ca(SCN)2  +  MnS  +  S  +  3  H20. 

Ammonium  sulphocyanide  and  potassium  ferrocyanide  are  now 
largely  obtained  from  the  spent  iron  oxide  from  the  purification 
of  illuminating  gas.  The  spent  oxide  is  first  lixiviated  with  warm 
water  (60°  C.),  until  the  liquor  has  a  density  of  from  1.07  to  1.085. 
The  solution,  containing  ammonium  sulphocyanide  and  other  am- 
monium salts,  is  evaporated  to  1.2  sp.  gr.,  and  cooled,  when  the 
associated  salts  (ammonium  sulphate,  etc.)  crystallize.  The  mother- 
liquor  is  further  concentrated,  and  impure  crystals  of  the  sulpho- 
cyanide separate,  which  are  purified  by  recrystallization.  Ammo- 
nium sulphocyanide  is  also  obtained  from  gas-liquor  by  treating 
the  non-volatile  residue  from  the  steam  distillation  (see  Ammonia) 
with  copper  and  iron  sulphates,  whereby  cuprous  sulphocyanide  is 
formed.  This  is  washed,  and  treated  with  ammonium  sulphide, 
forming  cuprous  sulphide  and  ammonium  sulphocyanide.  The 
latter  is  then  extracted  with  water. 

Ammonium  sulphocyanide  is  very  soluble  in  water  and  in  alcohol. 
It  is  used  as  a  source  of  other  sulphocyanides,  and  in  dyeing,  to  pre- 
vent the  injurious  action  of  iron  on  the  color. 

*  Dingler's  Polytechnisches  Journal,  245,  214. 


CYANIDES  249 

The  residue  from  the  lixiviation  is  mixed  with  quicklime  (which 
is  slaked  by  the  moisture  in  the  damp  mass),  and  heated  by  steam 
in  closed  vessels  to  100°  C.  The  lime  decomposes  the  ferric  ferrocy- 
anide  and  the  double  iron-ammonium  cyanides,  setting  free  ammonia 
gas,  which  is  absorbed  in  scrubbers,  and  forming  calcium  ferro- 
cyanide,  which  is  obtained  by  lixiviating  the  mass.  The  solution  of 
calcium  ferrocyanide  is  evaporated,  and  treated  with  the  calculated 
amount  of  potassium  chloride  to  form  the  difficultly  soluble  calcium- 
potassium  ferrocyanide,  CaK2Fe(CN)6.  This  is  separated  from  the 
mother-liquor,  washed,  and  decomposed  with  potassium  carbonate  to 
form  potassium  ferrocyanide. 

The  reactions  are  :  — 


1)  Fe4  SFe(CN)6|3  +  6  Ca(OH)2  =  3  Ca2Fe(CN)6  +  4  Fe(OH)2. 

2)  (NH4)3Fe3SFe(CN)6S3  +  6Ca(OH)2 

=  3  Ca2Fe(CN)6  +  3  Fe(OH)3  +  3  ISTH,  +  3  H20. 

3)  Ca2Fe(CN)6  +  2  KC1  =  CaK2Fe(CN)6  +  CaCl8. 

4)  CaK2Fe(CN)6  +  K2C03  =  K4Fe(CN)6  +  CaC03. 

Potassium  ferrocyanide,  K4Fe(CN")6  •  3  H20,  also  called  yellow 
prussiate  of  potash,  is  also  made  by  fusing  together  potassium  car- 
bonate, iron  borings,  and  nitrogenous  organic  matter  of  any  kind 
(horn,  hair,  blood,  wool  waste,  and  leather  scraps).*  The  potash  is 
fused  in  a  shallow  cast-iron  pan,  set  in  a  reverberatory  furnace, 
and  the  organic  matter,  mixed  with  from  6  to  8  per  cent  of  iron 
borings,  is  stirred  in,  in  small  portions  at  a  time,  until  about  1^ 
parts  of  the  mixture  for  each  part  of  potash  have  been  added.  The 
temperature  must  be  kept  high  enough  to  keep  the  mass  perfectly 
liquid,  but  not  hot  enough  to  volatilize  the  cyanogen  salts.  The 
reaction  is  violent  at  first,  and  when  the  liquid  remains  in  quiet 
fusion  the  process  is  ended,  and  the  melt  is  ladled  into  iron  pans  to 
cool.  The  mass,  containing  a  number  of  substances  (KCN,  K2C03, 
K2S,  FeS,  metallic  iron,  carbon,  etc.),  is  broken  up  into  lumps  the 
size  of  an  egg,  and  digested  with  water  at  85°  C.  for  several  hours. 
During  this  process,  reactions  take  place  between  the  potassium 
cyanide  and  iron  sulphide,  by  which  the  ferrocyanide  is  formed  :  — 

6  KCN  +  FeS  =  K2S  +  K4Fe(CN)6. 

Liebig  explains  the  reactions  during  the  fusions  as  follows: 
part  of  the  carbon  and  nitrogen  of  the  organic  matter  combine  to 

*  The  organic  refuse  is  sometimes  partially  charred  in  retorts,  by  which  much 
ammonia  is  driven  off  and  saved.  But  the  yield  of  ferrocyanide  is  then  less,  since 
the  nitrogen  content  of  the  char  is  small. 


250  OUTLINES  OF  INDUSTRIAL   CHEMISTRY 

form  cyanogen  (CN)2,  while  some  of  the  potash  is  reduced  by  the 
excess  of  carbon  to  metallic  potassium,  which  at  once  unites  with 
the  cyanogen  to  form  potassium  cyanide.  The  sulphur  in  the 
organic  matter  combines  with  the  iron,  forming  ferrous  sulphide. 
Finally,  on  lixiviating,  the  formation  of  the  ferrocyanide  takes 
place.  The  solution  is  evaporated  in  iron  pans  by  the  waste  heat  of 
the  furnace,  and  clarified  while  hot;  on  cooling,  the  crude  ferro- 
cyanide crystallizes,  and  is  purified  by  recrystallization.  The 
mother-liquors  yield  more  impure  salt  on  further  evaporation. 

Potassium  ferrocyanide  forms  splendid  large  lemon-yellow  crys- 
tals, having  3  molecules  of  crystal  water,  which  it  gives  off  at 
100°  C.,  and  is  converted  to  a  white  powder.  It  is  not  poisonous.  It 
is  largely  used  for  making  Prussian  blue ;  in  calico  printing,  and  in 
in  dyeing;  for  case-hardening  iron;  for  making  potassium  cyanide 
and  ferricyanide ;  and  to  a  small  extent  in  explosives,  and  as  a 
chemical  reagent. 

Barium  sulpho cyanide,  Ba(SCN)^,  is  made  by  heating  ammonium 
sulphocyariide  with  barium  hydroxide  solution,  under  slight  pressure. 
Ammonia  distills  off,  and  the  liquid  is  evaporated  to  yield  the  barium 
salt,  Ba(SCN)2  •  2  H,O. 

This  is  generally  used  for  making  potassium  and  aluminum  sul- 
phocyanides,  KSCN  and  A1(SCN)3,  which  are  used  in  textile  dyeing 
and  printing. 

Potassium  ferricyanide,  red  prussiate  of  potash,  K3Ee(ClST)6,  is 
usually  made  by  passing  chlorine  gas  into  a  solution  of  the  ferro- 
cyanide, until  ferric  chloride  no  longer  forms  a  precipitate,  only  pro- 
ducing a  brown  color  in  the  liquid.  It  may  also  be  made  by  exposing 
the  dry  powdered  ferrocyanide  to  chlorine  until  a  test  portion,  dis- 
solved in  water,  gives  nothing  but  a  brown  color  with  ferric  chloride. 

2  K4Fe(CN)6  +  2  01  =  2  KC1  +  2K3Fe(CN)6. 

Excess  of  chlorine  must  be  avoided,  since  this  forms  a  dirty 
green  precipitate  (Berlin  green)  in  the  solution,  which  cannot  be 
removed  by  filtering. 

Lunge  *  recommends  boiling  the  solution  of  ferrocyanide  with 
lead  peroxide,  while  passing  a  stream  of  carbon  dioxide  through 
the  liquor :  — 

2  K4Fe(CN)e  -f  H20  +  0  =  2  K3Fe(CN)6  +  2  KOH ; 
but  the  final  reaction  may  be  written :  — 

2  K4Fe(CN)6  +  Pb02  +  2  C02  =  2  K3Fe(CN)6  +  PbC03  +  K2C03. 

*  Dingler's  Polytecbnisches  Journal,  238,  75. 


CYANIDES  251 

An  excess  of  carbon  dioxide  is  necessary  to  prevent  decomposi- 
tion of  the  ferricyanide  by  the  lead  oxide  and  alkali. 

A  very  good  product  is  obtained  by  the  action  of  potassium  per- 
manganate on  a  mixture  of  calcium  and  potassium  ferrocyanide  solu- 
tions :  — 

3  Ca2Fe(CN)6  +  7  K4Fe(CN)6  +  2  KMn04 

=  10  K3Fe(CN)6  +  6  CaO  +  2  MnO. 

The  calcium  and  manganese  hydroxides  formed  are  but  slightly 
soluble,  and  are  easily  removed  from  the  solution  by  carbon  dioxide, 
and  the  ferricyanide  purified  by  crystallization. 

Potassium  ferricyanide  crystallizes  in  blood-red  prisms,  without 
crystal  water,  and  is  very  soluble,  forming  a  solution  of  an  intense 
yellow  color.  With  ferrous  salts,  it  gives  the  blue  pigment,  Turn- 
bull's  blue.  With  ferric  salt,  it  gives  a  brown  coloration,  but  no  pre- 
cipitate. Its  solution,  with  caustic  potash,  is  a  powerful  oxidizing 
liquid,  and  as  such  is  used  in  calico  printing  for  a  "  discharge  "  on 
indigo  and  other  dyes.  It  also  forms  part  of  the  sensitive  coating 
for  "blue  print"  papers.  It  has  been  recommended  for  use  with  the 
potassium  cyanide  solution  in  gold  extraction. 

Potassium  cyanide,  KCN,  is  generally  made  by  fusing  the  ferro- 
cyanide with  potassium  carbonate,  until  the  evolution  of  gas  ceases. 
The  following  is  the  reaction :  - 

K4Fe(CN)6  +  K2C03  =  5  KCK  -f  KCNO  +  C02  +  Fe. 

The  metallic  iron  separated  sinks  to  the  bottom  of  the  crucible,  and 
the  fused  mixture  of  cyanide  and  cyanate  is  run  off.  The  addition 
of  powdered  charcoal  reduces  part  of  the  cyanate  to  cyanide.  The 
product  is  pure  enough  for  many  purposes.  The  cyanate,  which  is 
sometimes  injurious,  may  be  reduced  by  the  action  of  metallic  zinc 
or  sodium,  or  the  cyanide  may  be  extracted  with  alcohol,  acetone,  or 
carbon  di sulphide. 

By  fusing  the  ferrocyanide  with  sodium  carbonate,  a  mixture  of 
sodium  and  potassium  cyanides  is  obtained,  which  is  extensively 
employed  in  the  arts  under  the  name  of  "cyan-salt."  This  is 
cheaper  than  the  pure  potassium  salt. 

Potassium  cyanide  is  also  made  by  fusing  the  dry  ferrocyanide 
in  closed  crucibles,  until  nitrogen  ceases  to  be  given  off.  Carbide  of 
iron  is  formed,  and  sinks  to  the  bottom  of  the  crucible,  if  the  fusion 
is  allowed  to  stand  for  a  considerable  time.  But  the  separation  is 
imperfect,  and  the  product  is  usually  dissolved  in  alcohol  or  acetone, 
and  the  clarified  solution  heated  in  a  still  to  recover  the  solvent. 


252  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

The  product  is  then  heated  until  it  fuses,  and  when  cold,  it  forms  a 
white,  transparent  mass.  Air  must  be  carefully  excluded  during 
the  whole  process,  to  prevent  the  formation  of  cyanate.  The  re- 
action is  :  — 

K4Fe(CN)6  =  4  KCN  +  FeC2  +  N2. 

But  the  product  is  not  entirely  free  from  potassium  carbonate, 
since  it  is  practically  impossible  to  evaporate  a  cyanide  solution 
without  some  decomposition  and  escape  of  hydrocyanic  acid.  The 
caustic  potash  thus  formed  then  combines  with  carbon  dioxide  from 
the  air.  Water  cannot  be  used  to  leach  the  iron  carbide  residue, 
since  the  potassium  cyanide  in  solution  at  once  recombines  with  the 
iron  to  form  ferrocyanide  again. 

Potassium  cyanide  is  made  from  the  sulphocyanide,  by  extract- 
ing the  sulphur  with  zinc  or  lead.*  The  zinc  is  melted  in  a  graphite 
vessel,  and  charcoal  powder  is  spread  over  its  surface.  The  sulpho- 
cyanide is  stirred  into  the  fused  metal  until  the  mass  becomes  a 
thick  paste,  when  it  is  allowed  to  cool.  It  is  then  systematically 
lixiviated  in  tanks  similar  to  Shank's  apparatus  (p.  76).  Any 
alkali  sulphide  is  precipitated  by  adding  lead  cyanide.  The  solu- 
tion is  evaporated  in  vacuum,  and  yields  an  impure  product,  con- 
taining cyanate  and  double  zinc-potassium  cyanide. 

Cyanides  are  also  produced  by  conducting  ammonia  gas  through 
vertical  retorts,  containing  charcoal  and  alkali  carbonate,  and  heated 
to  a  red  heat.  The  mass  is  then  withdrawn  from  the  retort,  lixivi- 
ated, and  the  solution  concentrated  to  1.4  sp.  gr.  Potassium  car- 
bonate is  added  to  the  cold  solution,  precipitating  the  potassium 
cyanide,  which  is  freed  from  mother-liquor  in  centrifugal  machines, 
and  recrystallized  :  — 

K2C03  +  C  +  2  NH3  =  2  KCN  +  3  H20. 

Castner  proposes  to  run  metallic  sodium  through  a  retort  filled 
with  coke,  while  passing  ammonia  gas  into  it.  The  reaction  is  said 
to  work  at  a  lower  temperature  than  in  other  processes. 


Many  other  patents  for  the  production  of  cyanides  have  been 
taken  out,  but  at  present  nearly  the  whole  supply  of  alkali  cyan- 
ides is  derived  from  potassium  ferrocyanide. 

Potassium  cyanide  comes  in  commerce  as  white  lumps  or  powder, 
very  soluble  in  water  and  having  alkaline  reaction.  It  smells  some- 
what like  bitter  almond  oil,  owing  to  the  prussic  acid  liberated  from 
it  by  the  action  of  carbon  dioxide  and  moisture  in  the  air.  On  stand- 

*  J.  Soc.  Chem.  Ind.,  1892,  14. 


CARBON  DISULPHIDE  253 

ing,  or  when  warmed,  its   aqueous   solution  decomposes,  forming 
ammonia  and  potassium  formate  :  — 


KCN  +  2  H20  =  NH3  +  HCOOK. 

The  commercial  salt  always  contains  cyanate  and  carbonate,  and 
is  sold  in  various  grades  for  particular  purposes.  The  best  quality 
is  about  98  to  99  per  cent  KCN,  but  ordinary  grades  contain  but 
65  or  70  per  cent.  It  is  a  very  powerful  reducing  material  when 
heated  with  reducible  substances,  and  hence  its  use  as  a  flux.  It  is 
extremely  poisonous,  both  when  taken  internally  and  when  intro- 
duced directly  into  the  blood.  It  is  extensively  employed  in  elec- 
troplating as  the  solvent  in  the  bath,  -as  it  forms  soluble  double 
cyanides  with  gold,  silver,  copper,  and  other  metals  ;  it  is  also  used 
as  a  flux  in  assaying  and  metallurgy  ;  its  greatest  use  at  the  present 
time  is  for  the  recovery  of  gold  from  low  grade  ores  and  tailings  of 
other  reduction  processes.  A  weak  solution  is  used  to  dissolve  the 
gold,  forming  aurous  potassium  cyanide,  AuCN,  KCN.  It  was  for- 
merly much  used  in  photography  for  "  fixing  "  the  image,  but  for 
this  purpose  it  has  been  largely  replaced  by  sodium  thiosulphate. 


CARBON  DISULPHIDE 

Carbon  disulphide,  CS2,  is  extensively  employed  as  a  solvent, 
especially  for  grease  and  oils.  It  is  made  by  passing  sulphur  vapor 
over  coke  or  charcoal,  which  has  been  heated  to  a  "  cherry  red  "  in  a 
vertical  retort  of  cast  iron  or  glazed  earthenware.  From  the  top  of 
the  retort,  a  wride  pipe  leads  to  a  vessel  in  which  uncombined  sul- 
phur vapor,  passing  out  with  the  carbon  disulphide,  is  condensed. 
The  carbon  disulphide  passes  on,  and,  condensing  in  a  Liebig's  con- 
denser, collects  under  water  in  a  receiver,  and  is  drawn  into  tanks, 
from  which  it  is  forced  by  compressed  air  into  storage  tanks  placed 
on  a  higher  level.  The  uncondensable  gases,  chiefly  hydrogen  sul- 
phide, are  led  from  the  receiver  into  a  tower  containing  plates  or 
shallow  trays,  over  which  vegetable  oil  trickles,  to  absorb  any  trace 
of  disulphide  vapor ;  then  they  go  into  a  second  tower,  containing 
layers  of  lime,  or  iron  oxide,  which  absorb  the  hydrogen  sulphide. 
When  sufficiently  charged,  the  oil  is  heated,  and  the  disulphide  dis- 
tills off ;  the  oil  is  then  returned  to  the  tower. 

Of  the  various  forms  of  apparatus  devised  for  making  carbon 
disulphide,  that  of  I.  Singer  *  is  one  of  the  best.  The  crude  disul- 

*  J.  Soc.  Chem.  Ind.,  1889,  93. 


254  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

phide  attacks  nearly  all  metals,  and  the  receiver,  tank,  and  pipes 
should  be  lined  with  lead.  Eetorts  of  cast  iron  are  made  very  heavy, 
but  are  rapidly  destroyed  by  the  action  of  the  sulphur.  Very  pure 
coke  or  charcoal  is  necessary,  and  it  should  be  heated  immediately 
before  charging  into  the  retort,  to  expel  any  absorbed  oxygen  or 
moisture,  since  these  combine  with  some  of  the  sulphur  vapor,  and 
form  impurities  in  the  product.  The  temperature  should  be  kept  as 
constant  as  possible,  at  a  red  heat.  The  sulphur  is  sometimes  intro- 
duced in  a  solid  state,  through  an  opening  near  the  bottom  of  the 
retort,  but  it  is  better  to  melt  it  in  a  separate  vessel,  and  allow  it  to 
flow  in  a  small  stream,  entering  the  retort  at  the  bottom.  It  has 
recently  been  proposed  to  vaporize  the  sulphur  before  it  enters  the 
retort,  the  chief  difficulty  then  being  to  prevent  its  passing  through 
the  retort  uncombined. 

The  crude  carbon  disulphide  is  impure,  and  has  a  very  offensive 
odor.  It  is  purified  by  forcing  lime-water  in  a  fine  spray,  from  a 
perforated  lead  coil,  through  the  carbon  disulphide  liquor,  until  the 
water  running  out  of  the  tank  is  clear.  This  removes  the  hydrogen 
sulphide,  and  the  washed  carbon  disulphide  is  then  mixed  with  a 
little  colorless  oil;  some  water,  containing  a  little  lead  acetate,  is 
added  to  remove  the  remaining  sulphur  impurities,  and  the  mixture 
is  distilled  on  a  steam  bath.  Sometimes  the  crude  product  is  puri- 
fied by  distilling  in  a  large  boiler  with  some  caustic  soda,  or  milk  of 
lime,  or  by  shaking  with  anhydrous  copper  sulphate,  and  then  re- 
distilling by  steam  heat. 

Carbon  disulphide  is  a  pale  yellow,  or  colorless,  heavy,  mobile 
liquid,  having  a  fetid  odor  when  impure,  boiling  at  46°  C.,  and 
extremely  volatile  at  ordinary  temperatures.  Its  vapors  inflame 
at  149°  C.,  are  very  heavy,  and  are  poisonous  when  breathed.  It  is 
sent  to  market  in  sheet  iron  cans,  or  drums,  and  is  regarded  as  dan- 
gerous freight  because  of  its  extreme  volatility,  and  the  explosive 
nature  of  its  vapor  when  mixed  with  air.  When  burned,  it  produces 
large  quantities  of  suffocating  gases  (C02,  S02).  It  is  very  slightly 
soluble  in  water,  but  mixes  well  in  all  proportions  with  ether,  ben- 
zene, alcohol,  and  many  oils.  It  dissolves  sulphur,  phosphorus, 
iodine,  camphor,  wax,  tar,  resins,  rubber,  and  nearly  all  oils  and 
fats.  Hence  its  use  as  a  solvent  and  extractive  agent  is  very  exten- 
sive. It  is  also  used  as  a  disinfectant ;  as  a  germicide  and  insecti- 
cide in  agriculture,  and  in  museums  and  herbariums ;  in  refrigerating 
machines  ;  for  exterminating  moles,  rats,  woodchucks,  and  other  bur- 
rowing animals;  in  the  manufacture  of  rubber  cement;  in  making 
cyanides  and  carbon  tetrachloride ;  and  in  organic  preparation  work. 


MANGANATES  AND  PERMANGANATES       255 


CARBON   TETRACHLORIDE 

Carbon  tetrachloride  is  made  by  passing  a  mixture  of  carbon 
disulphide  vapor  and  chlorine  through  a  red-hot  porcelain  tube.*  A 
mixture  of  sulphur  chloride,  S2C12,  and  carbon  tetrachloride  results, 
which  is  treated  with  milk  of  lime,  and  digested  with  potash,  and 
the  tetrachloride  distilled.  Or  dry  chlorine  may  be  led  into  carbon 
disulphide  containing  a  little  iodine  in  solution,  f  The  tetrachloride 
is  distilled  off,  and  washed  with  alkali,  to  remove  iodine  and  sulphur 
chloride. 

CS2  +  6  01  =  C014  +  S2C12. 

Carbon  tetrachloride  is  a  heavjr,  colorless  liquid,  boiling  at  76°  C. 
It  is  a  good  solvent  for  many  substances,  and  may  be  used  instead  of 
chloroform  or  carbon  disulphide  for  extractions.  It  is  not  inflamma- 
ble, and  is  less  poisonous  than  the  latter. 


MANGANATES  AND  PERMANGANATES 

Sodium  manganate,  Na2Mn04,  is  made  by  mixing  sodium  nitrate 
or  caustic  soda  solution,  with  powdered  pyrolusite,  or  manganese 
oxides,  evaporating  to  dryness,  and  calcining  the  mass  at  a  red  heat, 
with  access  of  air,  in  shallow  vessels.  The  following  is  the  reaction 
involved:  — 

Mn02  +  2  NaOH  -f  O  =  Na2Mn04  +  H20. 

The  product  of  the  fusion  is  a  dull  green,  porous  mass,  which,  if 
lixiviated,  yields  a  green  solution  of  the  manganate.  But  this  is 
unstable,  and  if  exposed  to  the  air,  or  treated  with  an  acid,  or  boiled, 
the  manganate  is  converted  into  permanganate :  — 

3  NaaMn04  +  2  H2O  =  2  NaMnO4  +  4  NaOH  +  Mn02. 

In  alkaline  solution,  however,  the  manganate  is  more  stable. 

Sodium  manganate  is  a  powerful  oxidizing  agent,  and  is  used  as 
a  disinfectant.  It  is  also  converted  to  the  permanganate,  and  sold  in 
solution  as  "  Condy's  liquid "  for  disinfecting  purposes.  Sodium 
permanganate  does  not  crystallize  well. 

Potassium  manganate,  K2Mn04,  is  very  similar  to  the  sodium 
salt,  and  is  made  in  the  same  way.  It  is  chiefly  used  in  preparing 
the  permanganate,  KMn04,  which  crystallizes  very  well.  This,  being 

*  Kolbe,  Annalen  der  Chemie  und  Pharmacie,  45,  41 ;  54,  145. 
t  Lever  and  Scott,  English  Patent  No.  18,990,  1889. 


256  OUTLINES  OF  INDUSTRIAL   CHEMISTRY 

easily  purified,  and  stable  when  crystallized,  is  the  most  important 
permanganate  of  commerce.  It  is  generally  made  by  decomposing 
potassium  manganate  with  sulphuric  acid,  carbon  dioxide,  or  with 
chlorine,  and  is  purified  by  recrystallizing. 

3  K2Mn04  +  2  H2S04  =  2  KMnO4  +  2  K2S04  +  Mn02  +  2  H20. 
3  K2Mn04  +  2  C02  =  2  KMn04  +  2  K2C03  +  Mn02. 
2  K2Mn04  +  C12  -  2  KMn04  +  2  KC1. 

Potassium  permanganate  forms  deep  purple,  prismatic  crystals, 
which  dissolve  in  16  parts  of  cold  water.  The  solution  has  a  power- 
ful oxidizing  action,  and  can  only  be  filtered  on  glass-wool  or  asbes- 
tos. When  mixed  with  organic  matter,  the  dry  powder  is  subject  to 
spontaneous  combustion,  and  forms  explosive  mixtures  with  easily 
oxidizable  substances.  It  is  used  as  a  disinfectant ;  in  bleaching  and 
dyeing ;  for  coloring  wood  a  deep  brown ;  for  purifying  ammonia  and 
carbon  dioxide  gases ;  and  in  medicine. 


PART   II 
ORGANIC  INDUSTRIES 


DESTKUCTIYE  DISTILLATION   OF  WOOD 

THE  properties  of  wood  have  been  considered  on  page  24.  It 
consists  mainly  of  cellulose  (C6H1005)n,  with  its  incrusting  layer  of 
lignin,  and  of  sap,  containing  water,  resins,  tannins,  coloring  matter, 
and  mineral  salts.  Air-dried  wood  contains  from  15  to  20  per  cent 
of  moisture.  When  heated  in  closed  retorts  away  from  the  air,  the 
cellulose  and  ligneous  matter  decompose  after  the  moisture  is  ex- 
pelled, and  a  large  number  of  substances  result,  only  a  few  of  which 
are  of  commercial  value.  These  crude  products  are  gases,  thin 
liquids,  viscous  liquids  or  tar,  and  charcoal.  When  wood  is  car- 
bonized in  pits  (p.  27).  the  volatile  products  go  to  waste.  But  by 
the  use  of  retorts,  which  is  rapidly  extending  to  all  countries,  the 
valuable  by-products,  liquid  distillates  and  tar,  are  saved ;  the  gases 
evolved  are  mainly  hydrogen,  methane,  ethane,  ethylene,  carbon 
monoxide,  and  carbon  dioxide ;  they  have  no  value  for  illuminating, 
and  are  generally  burned  under  the  retorts,  thus  economizing  fuel. 

When  wood  is  heated  in  retorts,  the  moisture  is  driven  out,  but 
no  decomposition  occurs  until  the  temperature  approaches  160°  C. 
Between  160°  and  275°  C.,  a  thin,  watery  distillate,  known  as 
" pyroligneous  acid,"  is  chiefly  formed;  above  275° C.  the  yield  of 
gaseous  products  becomes  marked,  and  between  350°  and  450°  C. 
liquid  and  solid  hydrocarbons  are  most  extensively  formed.  Above 
this  last  temperature,  little  change  occurs,  and  charcoal,  containing 
the  mineral  ash,  remains  in  the  retort. 

The  pyroligneous  acid  contains  the  important  liquid  distillates, 
methyl  alcohol  and  acetic  acid,  together  with  acetone,  methyl  acetate, 
allyl  alcohol,  phenols,  and  a  great  many  other  substances.  The  tar 
contains  aromatic  hydrocarbons  and  paraffines.  Its  most  valuable 
constituent  is  the  creosote  oil,  containing  guaiacol,  creosol,  and  other 
s  257 


258 


OUTLINES  OF  INDUSTRIAL  CHEMISTRY 


phenols  of  high  molecular  weight.     A  comparatively  small  amount 
of  phenol  or  carbolic  acid  is  present,  however. 

The  proportion  of  gaseous  products  to  liquid  distillate  and  char- 
coal is  largely  dependent  upon  the  method  of  heating  the  retort; 
by  rapid  heating  to  a  high  temperature,  the  quantity  of  gas  is  much 
increased ;  by  distillation  at  a  low  temperature,  the  yield  of  pyro- 

ligneous  acid,  tar,  and  charcoal 
is  greater.  The  variety  of  wood 
used,  affects  the  amount  of  acid 
|D  and  tar ;  deciduous  trees,  espe- 
cially birch,  oak,  and  beech,  are 
preferred ;  coniferous  woods 
yield  less  acid,  but  afford  a  tar 
(Stockholm  tar)  containing 
much  resin  and  turpentine. 
Since  the  yield  of  acid  and 

tar  is  increased  by  the  rapid  removal  of  the  vapors  from  the  retort, 
in  modern  plants  exhausters  are  used.  The  retorts  employed  are 
wrought-iron  cylinders  set  in  pairs,  in  brick  furnaces,  so  that  the 
flame  does  not  strike  directly  upon  them.  They  may  be  hori- 
zontal or  vertical.  The  horizontal  retort  (A),  Fig.  66*,  has  a  door 
at  the  front,  while  from  the  back  a  pipe  (B)  conducts  the  vapors 
to  the  condenser  (C),  from  which  the  uncondensed  gases  pass  through 
the  pipe  (D)  to  the  grate  and  are  burned.  The  condenser  is  made 
of  coils  of  copper  pipe,  surrounded  by  a  water  jacket  or  tank,  but 
having  the  elbows  outside  the  tank,  for  easy  removal  for  cleaning. 
The  wood  is  piled  by  hand  lengthwise,  in 
the  hot  retort,  after  the  charcoal  from  the 
previous  charge  has  been  drawn  into  a 
closed  vessel  to  cool.  When  distilling  conif- 
erous woods,  which  yield  much  tar,  a  tar 
separator  is  put  between  the  retort  and  the 
condenser.  The  pyroligneous  acid  is  col- 
lected in  wood  tanks,  where  tarry  matters 
deposit  on  standing. 

Vertical  retorts,  Fig.  67*,  are  made  in 
duplicate,  and  so  arranged  that  when  a 
charge  has  been  carbonized,  the  retort  (A) 
is  lifted  out  of  the  furnace  by  means  of  a 
crane  and  allowed  to  cool  unopened,  and 
another,  charged  with  fresh  wood,  is  at  once  put  into  its  place. 

*  J.  Soc.  Chem.  Ind.,  1897,  667  and  722  (M.  Klar). 


DESTRUCTIVE   DISTILLATION  OF   WOOD  259 

This  economizes  time  and  heat,  and  no  cooling  vessel  is  needed ;  but 
two  sets  of  retorts  are  required,  and  the  wear  from  frequent  moving 
is  considerable.  The  condenser  is  similar  to  that  described  above. 

Kilns  built  of  brick,  similar  to  the  beehive  coke  oven  (p.  28), 
but  provided  with  an  exit  pipe  for  the  volatile  products,  are  occa- 
sionally used,  but  less  successfully  than  the  iron  retorts. 

In  the  collecting  tanks,  the  pyroligneous  acid  separates  from  the 
tar,  which  settles  to  the  bottom.  The  yield  of  acid  is  about  30  per 
cent,  and  of  tar  about  10  per  cent  of  the  weight  of  the  dry  wood. 
The  acid  averages  about  10  per  cent  acetic  acid,  1  per  cent  methyl 
alcohol,  and  0.1  per  cent  acetone.  It  is  a  dark  red-brown  liquid, 
having  a  strong  ac;d  reaction  and  a  peculiar  empyreumatic  odor. 
Its  density  varies  according  to  the  nature  of  the  wood  distilled,  but 
usually  falls  between  1.020  and  1.050  sp.  gr.  It  finds  limited  use  in 
the  manufacture  of  an  impure  acetate  of  iron,  known  as  "  black  iron 
liquor  "  or  "  pyrolignite  of  iron."  But  for  most  purposes  it  is  puri- 
fied, to  separate  the  methyl  alcohol,  acetone,  and  acetic  acid.  The 
boiling  point  of  methyl  alcohol  is  66°  C.,  while  that  of  acetic  acid 
varies  from  100°  to  120°  C.,  according  to  the  amount  of  water  present. 
Hence  if  the  pyroligneous  acid  is  distilled,  and  the  receiver  changed 
when  the  temperature  approaches  100°  C.,  the  greater  part  of  the 
methyl  alcohol,  together  with  acetone,  methyl  acetate,  allyl  alcohol, 
etc.,  is  separated  from  the  acetic  acid  and  its  homologues.  But 
usually  the  vapors  from  the  distillation  are  passed  through  milk  of 
lime,  which  combines  with  the  acetic  acid  to  form  calcium  acetate, 
while  the  alcohol  vapors  pass  on  and  are  condensed.  Most  of  the 
tarry  matter  remains  in  the  still.  If  the  solution  of  calcium  acetate 
thus  formed  is  filtered  and  evaporated  to  dryness,  the  salt  is  ob- 
tained in  a  commercial  form,  known  as  "gray  acetate  of  lime." 
During  the  evaporation  much  of  the  tar  and  oily  impurities  rise  to 
the  surface  and  are  removed  by  skimming.  The  tarry  matters 
remaining  in  the  acetate  decompose  during  the  drying  process.  If 
the  pyroligneous  acid  is  neutralized  with  lime  before  distilling  off 
the  methyl  alcohol,  the  resulting  calcium  acetate  is  contaminated 
with  much  tar,  and  when  evaporated  to  dryness  forms  the  commer- 
cial "  brown  acetate  of  lime." 

The  crude  methyl  alcohol,  wood  naphtha,  or  wood  spirit,  is  purified 
by  diluting  with  water  until  it  becomes  milky,  owing  to  the  separa- 
tion of  oily  impurities  (ketones  and  hydrocarbon  oils),  which  collect 
in  a  separate  layer  on  standing,  and  are  removed.  The  liquid  is 
then  redistilled  over  lime  in  a  rectifying  still  (p.  9).  The  lime 
fixes  the  traces  of  acid  and  decomposes  methyl  acetate.  The  recti- 


260  OUTLINES  OF   INDUSTRIAL  CHEMISTRY 

fied  spirit  is  usually  filtered  through  a  tower  containing  charcoal, 
to  remove  the  coloring  matter  and  unpleasant  odor  as  much  as  pos- 
sible. By  distilling  again,  over  lime,  methyl  alcohol  of  99  per  cent 
is  obtained.  Acetone  boils  at  56.3°  C.,  and  is  not  removed  from 
the  methyl  alcohol  by  distillation  or  treatment  with  lime.  Hence 
the  alcohol  is  treated  with  chlorine,  which  combines  with  the  acetone, 
forming  chlor-acetones,  having  high  boiling  points,  and  from  which 
the  alcohol  is  separated  by  distillation.  Or  iodine  and  caustic  soda 
may  be  added ;  these  react  with  the  acetone  to  form  iodof orm,  which 
precipitates.  If  calcium  chloride  is  added,  it  combines  with  the 
alcohol  to  form  a  crystallized  solid  which  is  stable  at  100°  C.  This  is 
gently  heated  until  the  acetone  is  driven  out,  and  is  then  treated 
with  hot  water  under  pressure ;  the  calcium  chloride  compound  is 
decomposed  and  the  methyl  alcohol  distills  off. 

Commercial  methyl  alcohol  is  often  slightly  yellowish  in  color 
and  generally  has  a  disagreeable  odor.  It  is  largely  used  as  a  solv- 
ent in  varnish  making,  for  which  purpose  the  presence  of  acetone 
is  desirable,  and  in  the  coal-tar  dye  manufacture,  where  a  pure  alco- 
hol, free  from  acetone,  is  required.  In  European  countries  crude 
wood  spirit  is  much  used  for  mixing  with  ethyl  alcohol,  to  prepare 
"methylated  spirit,"  or  "denaturated  ethyl  alcohol"  (p.  409). 

Acetone,  when  recovered  from  wood  spirit,  is  generally  distilled 
from  the  calcium  chloride  compound  with  the  methyl  alcohol.  It  is, 
however,  generally  prepared  by  the  dry  distillation  of  calcium  ace- 
tate :  — 

(C2H302)2Ca  =  CaC03  +  CH3  -  CO  -  CH3. 

The  product  obtained  by  either  of  the  above  methods  is  crude ; 
sodium  bisulphite  is  added,  and  combines  with  the  acetone  to  form 
a  double  salt,  which  is  readily  purified  by  crystallization  from  aque- 
ous solution.  This  is  then  decomposed  by  heating  with  sodium  car- 
bonate solution,  setting  free  the  acetone,  which  is  distilled  off  in  a 
very  pure  state. 

A  commercial  method  for  the  production  of  acetone,  devised  by 
Dr.  E.  B.  Squibb,*  consists  in  passing  acetic  acid  vapor  through  a 
rotating  iron  cylinder,  heated  to  about  500°- 600°  C.,  and  containing 
pumice  stone  with  precipitated  barium  carbonate.  On  leaving  the 
still  the  vapors  pass  through  a  fractional  condensation  apparatus, 
to  remove  water  and  acetic  acid ;  the  dilute  acetone  condenses  in  a 
second  condenser.  This  is  a  good  solvent  for  many  substances,  and 
may  be  used  for  making  chloroform.  The  reaction  is :  — 

2  C2H402  =  H20  +  CH3  -  CO  -  CH3  +  C02. 
*  J.  Am.  Chem.  Soc.,  17, 187. 


DESTRUCTIVE   DISTILLATION   OF   WOOD  261 

The  barium  carbonate  acts  merely  as  a  contact  body,  since  the  tem- 
perature is  always  above  that  at  which  barium  acetate  decomposes. 

Acetone  is  a  colorless  mobile  liquid,  having  a  peculiar  odor  and 
unpleasant  taste.  It  boils  at  56.3°  C.,  and  mixes  with  water  in  all 
proportions.  It  is  an  excellent  solvent  for  many  resins,  gums,  and 
other  organic  substances.  It  is  much  used  for  preparing  chloroform, 
iodoform,  and  the  medicinal  preparation,  sulphonaL  In  Europe  it  is 
also  used  in  the  denaturation  of  ethyl  alcohol. 

Commercial  acetic  acid  is  prepared  from  gray  or  brown  acetate  of 
lime*  (p.  259)  by  distilling  with  concentrated  hydrochloric  acid,  in 
copper  stills,  care  being  taken  to  have  an  excess  of  lime  salt  in  the 
retort.  Thus  the  calcium  acetate  is  decomposed,  and  acetic  acid, 
with  calcium  chloride,  results.  The  acid  is  a  slightly  colored  liquid, 
containing  about  50  per  cent  anhydrous  acid.  It  may  be  further 
purified  by  distilling  again,  over  a  little  potassium  bichromate,  and 
filtering  through  freshly  burned  charcoal.  If  the  hydrochloric  acid 
is  diluted  before  heating  it  with  the  calcium  acetate,  the  distillate 
contains  only  30  per  cent  C2H402,  and  is  much  purer,  usually  requir- 
ing no  second  distillation  for  technical  uses.  Stronger  acid  may  be 
made  by  neutralizing  the  50  per  cent  acid  with  lime,  evaporating  to 
dryness,  and  again  decomposing  with  concentrated  hydrochloric 
acid. 

When  pyroligneous  acid  is  distilled  without  neutralizing  with 
lime,  the  distillate  collected  between  100°  and  120°  C.  is  a  dilute  and 
highly  colored  liquid,  known  as  "wood  vinegar."  This  contains  a 
little  tar  and  empyreumatic  matter,  and  is  used  for  some  technical 
purposes,  but  is  generally  purified  by  converting  it  to  the  calcium 
salt  and  distilling  with  mineral  acid,  as  above. 

Sulphuric  acid  is  not  generally  used  to  decompose  calcium  acetate, 
because  the  calcium  sulphate  is  difficult  to  remove  from  the  still. 
Also,  the  impurities  present  frequently  cause  reduction  of  sulphuric 
acid,  contaminating  the  product  with  sulphurous  acid. 

Since  soda-ash  is  now  cheap,  it  is  generally  used,  instead  of  lime, 
for  the  neutralizing.  Sodium  acetate  may  be  purified  by  crystalliz- 
ing, or  it  may  be  fused  without  decomposing,  to  destroy  the  tarry 
matters.  It  may  be  decomposed  with  sulphuric  acid,  since  sodium 
sulphate  is  readily  removed  from  the  still. 

Fused  sodium  acetate  may  be  decomposed  by  distilling  with  con- 
centrated sulphuric  acid  at  120°  C. ;  the  sulphuric  acid  absorbs  any 
moisture,  and  the  very  concentrated,  nearly  anhydrous  glacial  acetic 

*  Brown  acetate  of  lime  is  calcined  at  230°  C.,  to  destroy  tarry  matters  before  de- 
composing with  the  hydrochloric  acid. 


262  OUTLINES    OF  INDUSTRIAL  CHEMISTRY 

acid,  which  crystallizes  if  cooled  to  16.5°  C.,  is  obtained.  This  is  also 
made  from  calcium  acetate,  by  decomposing  the  latter  in  solution 
with  sodium  sulphate,  filtering  off  the  calcium  sulphate,  evaporating 
the  sodium  acetate  solution  to  dryness,  and  fusing.  The  fused  salt 
is  distilled  with  oil  of  vitriol  as  above  described,  and  the  sodium 
sulphate  so  formed  is  used  to  decompose  more  lime  salt. 

Common  acetic  acid  of  commerce  is  a  slightly  colored  liquid  of 
about  1.040  sp.  gr.  (8°  Tw.),  and  containing  approximately  30  per 
cent  anhydrous  acid.  It  is  used  in  the  preparation  of  acetates,  in 
the  manufacture  of  white  lead,  and  in  pharmacy.  Stronger  acid  is 
used  in  coal-tar  color  making  and  for  preparing  ethyl  acetate  for  a 
solvent  of  nitrocellulose  in  manufacturing  explosives.  Some  pure 
acetic  acid  from  wood  distillate  is  used  for  vinegar,  but  lacks  the 
characteristic  salts  and  flavoring  substances  present  in  true  fermen- 
tation vinegar  (p.  415). 

Acetates.  —  Aluminum  acetate  in  the  pure  state  is  not  known,  but 
a  solution  of  it  in  acetic  acid,  called  "  red  liquor,"  is  largely  used  in 
dyeing  and  in  calico  printing.  It  is  made  by  dissolving  aluminum 
hydroxide  in  acetic  acid,  or  by  decomposing  lead  or  calcium  acetates 
with  aluminum  sulphate  or  alum  :  — 

A12(S04)3  +  3  Pb  (C2H302)2  =  2  Al  (C2H302)3  +  3  PbS04. 

Calcium  acetate  yields  the  best  red  liquor ;  that  made  from  lead 
acetate  is  not  entirely  free  from  lead,  which  dulls  the  shade  of  deli- 
cate colors ;  when  made  from  alum  it  contains  sulphate  of  the  alkali 
metal,  and  decomposes  more  readily  than  when  made  from  aluminum 
sulphate.  Several  basic  aluminum  acetates  are  made  by  adding 
sodium  carbonate  to  the  normal  acetate  solution.  These  deposit 
alumina  on  the  fibre  very  readily. 

Chromium  acetate  finds  some  use  as  a  mordant  in  calico  printing. 
It  is  usually  made  by  dissolving  chromium  hydroxide  in  acetic  acid, 
or  by  decomposing  a  solution  of  chromium  sulphate  or  chrome  alum 
with  lead  or  calcium  acetate.  The  solution  is  violet,  but  becomes 
green  if  heated.  It  may  be  evaporated  to  dryness  without  rendering 
the  salt  insoluble,  and  the  solution  does  not  dissociate.  Alkalies 
and  alkaline  carbonates  yield  no  precipitate  in  the  cold  solution,  but 
when  heated,  a  precipitate  of  chromium  hydroxide  forms. 

Basic  acetates  are  prepared  by  adding  lead  or  calcium  acetate  to 
basic  chromium  sulphate  solution.  Sulphate-acetates  are  also  made 
and  used  as  mordants. 

Calcium  acetate  has  been  mentioned  as  brown  or  gray  acetate  of 
lime  (p.  259).  The  pure  salt,  occasionally  used  as  a  mordant,  is 


DESTRUCTIVE   DISTILLATION  OF   WOOD  263 

made  by  neutralizing  acetic  acid  with  the  theoretical  quantity  of 
lime.  Litmus  does  not  show  the  point  of  neutrality.  The  crystal- 
lized salt,  Ca  (C2H302)2  •  H2O,  is  very  soluble  in  water. 

Cupric  acetate,  Cu  (C2H302)2  •  H20,  is  best  made  by  adding  lead 
acetate  to  copper  sulphate  solution  :  — 

CuS04  +  Pb  (C2H302)2  =  Cu  (C2H302)2  +  PbS04. 

It  may  be  made  by  dissolving  verdigris,  or  copper  carbonate  or 
oxide,  in  acetic  acid.  For  basic  acetates  see  p.  204. 

Ferrous  acetate,  Fe  (C2H302)2  •  4  H20,  may  be  prepared  from  cop- 
peras and  lead  or  calcium  acetate ;  or  by  dissolving  scrap  iron  in 
acetic  acid.  It  is  quickly  oxidized  in  the  air  to  basic  ferric  acetate. 
"  Pyrolignite  of  iron,"  black  liquor,  or  iron  liquor,  is  made  by  dissolv- 
ing scrap  iron  in  pyroligneous  acid.  It  is  sold  as  a  dirty  olive-brown 
or  black  liquid,  having  a  density  of  about  25°  Tw.,  and  consists 
mainly  of  ferrous  acetate,  with  some  ferric  acetate  and  tarry  matter. 
It  is  used  as  a  mordant  in  dyeing  black  silks  and  cottons,  and  in 
calico  printing. 

Ferric  acetate,  Fe2  (C2H302)6 ,  made  by  adding  lead  acetate  to  fer- 
ric sulphate,  is  stable  in  cold  solution.  It  forms  basic  salts  when 
treated  with  caustic  soda.  It  was  formerly  used  in  black  silk 
dyeing. 

Sodium  acetate,  NaC2H302  •  3  H20,  forms  needle-like  crystals 
which  melt  in  their  crystal  water  when  heated ;  when  anhydrous  it 
fuses  without  decomposition.  It  is  chiefly  used  for  making  pure 
concentrated  acetic  acid,  in  making  certain  diazo  bodies,  and  as  a 
developer  for  the  azo-dyes,  in  which  the  color  is  made  on  the  fibre. 

Lead  acetate,  Pb (C2H302)2  •  3  H,0,  "sugar  of  lead,"  is  made  by 
dissolving  litharge  in  acetic  acid.  If  wood  vinegar  is  used,  the 
product  is  "brown  sugar  of  lead."  With  an  excess  of  litharge,  basic 
acetates  are  formed.  The  normal  salt  is  very  soluble  in  water,  and 
is  used  for  making  other  mordants  and  for  chrome  yellows.  The 
salts  are  poisonous,  and  are  affected  by  the  carbon  dioxide  and 
hydrogen  sulphide  in  the  air. 


Wood-tar  varies  somewhat  in  character  with  the  kind  of  wood 
carbonized.  It  is  washed  with  hot  water,  or  treated  with  milk  of 
lime,  to  remove  acetic  acid,  and  then  washed  with  very  dilute  sul- 
phuric acid.  Excess  of  water  is  evaporated  by  warming  in  steam- 
jacketed  vessels.  The  tar  is  then  distilled  in  iron  stills,  provided 
with  stirring  apparatus,  the  temperature  being  raised  very  slowly. 


264  OUTLINES   OF  INDUSTRIAL   CHEMISTRY 

The  distillate  collected  below  150° C.  is  called  "light  oil,"  and  is 
chiefly  used  as  a  substitute  for  oil  of  turpentine  in  varnish  and 
paints.  Between  150°  and  250°  C.  the  "  heavy  oil "  is  collected,  con- 
taining creosote,  toluene  and  paraffine  bodies.  By  stopping  the  dis- 
tillation at  250°  C.,  a  thick,  brownish  liquid  is  obtained,  which  is 
used  in  making  axle  grease,  shoemakers'  wax,  for  lampblack,  and 
for  coating  the  interior  of  casks  and  barrels  to  render  them  impervi- 
ous to  liquids. 

The  creosote  oil  is  washed  with  caustic  soda,  and  boiled  in  the  air 
to  oxidize  various  substances  which  it  contains.  The  alkaline  solu- 
tion is  then  acidified  with  sulphuric  acid,  to  precipitate  the  creosote, 
which  is  treated  with  alkali  and  acid  as  before.  It  is  then  distilled 
again,  and  the  distillate,  collected  between  200°  and  220°  C.,  is  the 
commercial  wood-tar  creosote.  It  has  a  strong,  smoky  odor,  is  a 
good  antiseptic,  and  is  not  poisonous. 

Stockholm  tar  and  pine  tar  are  obtained  by  a  crude  distillation  of 
pitch-pine  or  other  coniferous  wood,  in  heaps,  covered  with  turf. 
These  are  of  different  composition  from  retort  tar,  and  are  mainly 
used  for  tarred  ropes,  with  oakum  for  ship  calking,  and  for  pre- 
serving timber. 

REFERENCES 

Das  Holz  und  seine  Distillations-Producte.  Dr.  G.  Thenius,  Leipzig,  1880. 
(Hartleben.) 

Die  Meiler  und  Retorten  Verkohlung.     Dr.  G.  Thenius. 

Das  Chemische  Technologic  der  Brennstoffe.  F.  Fischer,  Braunschweig,  1880. 
(Vieweg  u.  Sohn. ) 

Die  Verwerthung  des  Holzes  auf  chemischen  Wege.  Joseph  Bersch,  Leipzig, 
1883.  (Hartleben.) 

Destructive  Distillation.    E.  J.  Mills,  London,  1892.     (Gurney  and  Jackson.) 

Handbuch  der  Organ ischen  Chemie.  Victor  Meyer  and  Paul  Jacobson.  Vol. 
I.  Articles  —  "  Essigsaure  "  and  "  Methylalkohol. "  Leipzig,  1893.  (Viet 
u.  Cie.) 

Handbuch  der  Organischen  Chemie.  F.  Beilstein.  Vol.  1.  3d  Ed.  Purifica- 
tion of  Wood  Spirit.  Leipzig,  1894.  (L.  Voss.) 

Jahres-Bericht  liber  die  Leistungen  der  technischen  Chemie :  — 

1892.  F.  W.  Lefelmann.     (Distillation  of  Wood.) 

1893,  14.     J.  Sartig.     (Distillation  of  Wood.) 
Journal  of  the  Society  of  Chemical  Industry  :  — 

1892,  395  and  872.    John  Chorley  and  Wm.  Kamsay. 
1897,  667,  722.     M.  Klar.     (Modern  Distillation  of  Wood.) 


ILLUMINATING   GAS  265 


DESTRUCTIVE   DISTILLATION   OF   BONES 

Bones  are  usually  extracted  with  benzine  or  with  carbon  disul- 
phide,  and  the  fatty  matter  used  for  soap  stock.  They  still  contain 
nitrogenous  organic  substances,  and  are  distilled  in  iron  or  clay 
retorts,  similar  to  those  used  in  coal-gas  making  (p.  268),  yielding 
volatile  products,  consisting  of  gases,  ammonium  salts,  and  bone  oil ; 
these  pass  through  condensers,  where  the  water  and  bone  oil  con- 
dense; the  gases  pass  into  a  receiver  containing  sulphuric  acid, 
which  takes  up  the  ammonia  and  its  volatile  compounds;  the  in- 
flammable gases  are  burned  under  the  retort. 

The  bone  oil  ("  Dippel's  oil ")  and  aqueous  liquor  collected  under 
the  condensers  are  separated  by  gravity.  The  liquor  contains  am- 
monium carbonate,  cyanide,  sulphocyanide,  and  sulphide,  and  is 
treated  in  the  same  way  as  gas  liquor  (p.  125)  for  the  recovery  of  the 
ammonia.  The  crude  bone  oil  is  a  dark-colored,  foul-smelling  liquid, 
lighter  than  water.  It  is  redistilled  and  divided  into  numerous 
fractions.  At  high  temperatures  it  also  yields  ammonium  carbonate 
and  cyanide;  the  thick  tar  remaining  in  the  still  is  the  basis  of 
commercial  Brunswick  black. 

The  constituents  of  bone  oil  are  exceedingly  numerous,  but  the 
most  important  are  pyrrol,  C4H4NH;  pyridine,  C5H5N ;  picoline, 
C5H4(CH3)N;  lutidine  (dimethylpyridine)  ;  collidine,  C5H2(CH3)3]Sr ; 
and  quinoline,  C6H4  •  C3H3K  These  have  but  little  technical  use,  but 
are  employed  in  Europe  for  denaturating  alcohol,  and  in  the  prepara- 
tion of  certain  antiseptics.  They  are  closely  related  to  some  of  the 
alkaloids,  but  are  not  as  yet  used  to  prepare  them. 

The  residue  from  the  bone  distillation  is  the  bone-black  or  bone- 
char  of  commerce.  It  forms  about  65  per  cent  of  the  original 
weight  of  the  bones  and  consists  largely  of  calcium  phosphate  and 
carbonate,  impregnated  with  free  carbon.  While  still  hot,  it  is 
drawn  from  the  retort  into  closed  vessels  and  cooled  out  of  contact 
with  the  air.  It  is  largely  used  in  decolorizing  sugar  solutions, 
glucose,  glycerine,  oils,  paraffine,  vaseline,  etc.  It  loses  its  effec- 
tiveness after  a  time,  and  is  then  "revivified"  (p.  369).  When  it 
becomes  too  finely  powdered  for  successful  filtration,  it  is  used  as  a 
fertilizer  (p.  139). 

ILLUMINATING  GAS 

Illuminating  gas  may  be  made  by  enriching  water  gas  with  oil 
gas,  or  by  the  destructive  distillation  of  coal,  wood,  or  petroleum. 


266  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


Coal  gas,  such  as  is  generally  used  at  the  present  timp,  was  first 
employed  for  house  illuminating  by  William  Murdock,  in  London,  in 
1792.  It  was  introduced  for  street  lighting  in  -London  in  1812,  and 
in  Paris  in  1815.  In  this  country,  the  so-called  water  gas,  enriched 
with  naphtha,  has  largely  replaced  coal  gas  in  many  of  the  large 
cities.  This  has  greater  illuminating  power,  requires  a  smaller 
plant  and  less  labor,  and  ensures  greater  economy  of  working. 

Water  gas  is  produced  by  the  action  of  steam  on  incandescent 
carbon,  according  to  the  reactions  :  — 


C  +  C02  =  2  CO. 

It  is  composed  chiefly  of  hydrogen  and  carbon  monoxide,  is  non- 
luminous,  and  has  a  high  heat  value. 

Luminosity  depends  on  the  presence  of  hydrocarbons,  such  as 
ethane,  C2H6,  ethylene  (ethene),  C2H4,  acetylene  C2H2,  and  benzene, 
C6H6,  and  their  homologues,  the  most  important  of  these  "illu- 
minants  "  being  ethylene  and  benzene.  In  order  to  render  the  water 
gas  luminous,  it  is  carburetted  with  gases  derived  from  oil,  which  are 
rich  in  illuminants. 

Illuminating  water  gas  is  now  made  by  two  general  methods: 
(a)  the  carburetted  gas  is  made  in.  one  operation;  (6)  non-luminous 
gas  is  prepared,  and  then  carburetted  by  a  second  process.  The  first 
method  is  most  successfully  carried  out  by  the  Lowe  process.  The 
generator  (Fig.  68)  is  filled  with  anthracite  coal  or  coke,  which  is 
brought  to  incandescence  by  a  blast  of  air.  The  gases  from  the 
generator,  at  this  time  consisting  mainly  of  carbon  monoxide  and 
nitrogen,  enter  at  the  top  of  the  carburettor,  a  circular  chamber 
lined  with  firebrick,  and  containing  a  "  checker-work  "  of  the  same 
material  ;  while  passing  down  through  this,  the  producer  gas  (p.  30) 
is  partly  burned  by  an  air  blast  which  enters  the  apparatus  near  the 
top,  and  the  checker-work  is  heated  white  hot.  The  gases  pass  on 
to  the  "  superheater,"  a  taller  chamber,  also  filled  with  checker-  work. 
At  the  bottom  of  this  an  air  blast  is  introduced  to  complete  the 
burning  of  the  producer  gas  and  to  raise  the  temperature  of  the 
checker-work  to  a  very  bright  red  heat.  From  the  top  of  the  super- 
heater, the  waste  gases  escape  into  a  hood  leading  into  the  open  air. 
When  both  the  carburettor  and  superheater  have  reached  the  desired 
temperature,  the  air  blasts  are  cut  off,  and  steam  is  introduced  into 
the  generator,  where  it  is  decomposed  by  the  incandescent  fuel, 
according  to  the  reactions.  The  water  gas  thus  formed  passes  into 
the  carburettor,  while  a  small  stream  of  oil  is  being  introduced 


ILLUMINATING   GAS 


267 


through  a  pipe  at  the  top.  The  oil  is  decomposed  by  contact  with 
the  hot  checker-work,  forming  illuminating  gases  which  mix  with 
the  water  gas,  and  passing  into  the  superheater,  are  completely  fixed 
as  non-condensable  gases. 


FIG.  68. 


It  is  customary  to  run  the  air  blast  for  some  eight  minutes,  when 
the  fuel  reaches  a  temperature  of  about  1100°  C.  The  steam,  super- 
heated before  entering  the  generator,  is  run  about  six  minutes,  until 
the  temperature  of  the  generator  and  carburettor  has  fallen  below 
the  point  at  which  decomposition  occurs.  In  order  to  economize 
heat,  the  hot  carburetted  gas  is  passed  through  a  pipe  surrounded 
by  a  jacket,  within  which  the  oil  is  circulating,  thus  heating  it  be- 
fore it  enters  the  carburettor.  The  lower  end  of  the  pipe  leading 
from  the  superheater  is  closed  by  a  water  seal,  to  prevent  any  back- 
ward rush  of  the  gas  during  the  operation  of  the  air  blast.  It  is  cus- 
tomary to  lead  the  gas  from  the  superheater  into  a  storage  holder, 
from  which  it  is  drawn  through  the  purifying  apparatus. 

In  this  process,  the  blowing  of  air  and  of  steam  are  intermittent, 
but  the  actual  formation  of  gas  is  accomplished  in  one  operation. 


268  OUTLINES  OF  INDUSTRIAL   CHEMISTRY 

The  second  method  of  preparing  illuminating  water  gas  is  the 
Wilkinson  process.  Water  gas  is  made  by  blowing  steam  into  the 
hot  coal  in  the  generator,  and  is  stored  in  the  holder.  A  measured 
quantity  of  gas  is  then  introduced  into  the  carburettor,  a  closed  iron 
box,  containing  slightly  inclined  plates,  over  which  the  exact  amount 
of  oil  necessary  to  carburet  the  gas,  is  flowing  in  very  thin  layers. 
The  carburettor  is  also  provided  with  a  steam  jacket  and  coils  to 
keep  the  temperature  high  enough  to  vaporize  the  oil.  These  vapors 
mix  with  the  gas  and  pass  at  once  into  the  fixing  apparatus,  which 
is  a  long,  narrow,  fire-clay  retort,  kept  at  a  white  heat  by  external 
fire.  Here  the  oil  vapors  are  "  cracked  "  into  hydrocarbons,  which 
are  non-condensable  gases,  and  being  mixed  with  water  gas,  render 
it  luminous  when  burned.  The  mixed  gases  then  go  directly  to  the 
scrubbers  and  purifiers.  For  1000  cubic  feet  of  gas,  about  50  pounds 
of  anthracite  and  4.2  to  5  gallons  of  naphtha  are  consumed. 

The  impurities  in  the  water  gas  are  essentially  the  same  as  those 
in  coal  gas,  and  the  method  of  washing  and  purifying  are  the  same. 

The  illuminating  value  of  coal  gas  is  frequently  raised  by  mixing 
it  with  carburetted  water  gas.  Owing  to  its  high  percentage  of  car- 
bon monoxide,  water  gas  is  exceedingly  poisonous  when  inhaled,  and 
much  care  is  necessary  to  prevent  leakage  into  inhabited  rooms  (see 
table,  p.  278). 


Coal  gas,  prepared  by  the  destructive  distillation  of  bituminous 
coal,  is  generally  made  by  the  smaller  gas  companies  in  this  country. 
In  Europe  scarcely  any  water  gas  is  made  for  illuminating  purposes. 
The  composition  and  yield  of  coal  gas  depends  upon  the  kind  of  coal 
used  and  the  manner  of  distillation.  A  "  fat "  coal,  moderately  low 
in  sulphur  and  caking  on  distillation  to  a  good  coke  (e.  g.  the  Penn- 
sylvania gas  coals),  is  most  desirable  for  illuminating  gas.  The 
temperature  of  the  retort  is  a  very  important  factor  in  the  character 
of  the  distillation  products.  When  it  is  low,  the  quantity  of  gas 
formed  is  small,  but  it  contains  a  large  percentage  of  illuminants, 
and  hence  is  of  a  high  candle  power.  When  the  temperature  in  the 
retort  is  high  the  effects  are  as  follows :  —  (a)  the  yield  of  gas  is 
much  increased,  but  the  percentage  of  methane,  ethane,  and  hydrogen 
is  much  greater,  and  since  these  have  very  little  illuminating  value, 
the  gas  is  of  low  candle  power ;  (6)  the  yield  of  tar  is  increased ;  (c) 
the  vapors  of  the  heavy  hydrocarbons  which  constitute  some  of  the 
tar  are  decomposed  on  coming  in  contact  with  the  hot  retort,  form- 
ing gases  of  lower  carbon  content,  and  depositing  free  carbon  on  its 


ILLUMINATING   GAS 


263 


walls.  This  "  gas  carbon  "  *  adheres  very  firmly  and  if  allowed  to 
become  thick  causes  much  loss  of  heat.  It  is  especially  liable  to 
deposit  if  there  is  undue  pressure  in  the  retort,  which  may  be  the 
case  if  the  exhausters  are  not  working  properly ;  (d)  there  is  a  larger 
yield  of  organic  bodies  having  ring  nuclei  in  their  composition,  such 
as  benzene,  naphthalene,  phenols,  anthracene,  etc.  These  not  only 
cause  loss,  but  also  cause  clogging  in  the  service  pipes  and  burners. 

The  products  of  the  distillation  are  gas,  ammoniacal  liquor,  tar, 
and  coke.  When  coal  is  distilled  for  coke  (p.  27),  the  ammoniacal 
liquor  and  tar  are  sometimes  saved  by  the  use  of  by-product  ovens, 
but  the  gases  are  burned  for  fuel  or  go  to  waste.  When  distilled  for 
illuminating  gas,  the  process  is  carried  on  with  a  view  to  the  best 
yield  of  high  quality  gas,  but  the  ammoniacal  liquor,  tar,  and  coke 
are  valuable  by-products.  The  coke  is  too  soft  for  metallurgical 
purposes,  and  is  chiefly  used  to  heat  the  retorts  or  sold  for  domestic 
fuel. 


FIG.  69. 

A  diagram  of  a  complete  plant  for  coal  gas  making  is  shown  in 
Fig.  69.  The  retorts,  (A),  are  Q-shaped,  fire-clay  vessels,  about  8 
feet  long,  18  inches  wide,  and  15  inches  high ;  they  are  set  six  or 
eight  together  in  a  furnace,  the  whole  constituting  what  is  called  a 

*Gas  carbon  is  much  used  for  electric  light  carbons,  battery  plates,  and  other 
electrical  appliances.  It  is  denser  and  purer  than  most  other  forms  of  carbon. 


270  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

"bench."  Each  retort  has  a  cast-iron  mouthpiece  projecting  out  of 
the  furnace,  and  carrying  the  door,  closed  by  a  screw  clamp.  Ke- 
torts  may  be  "  single,"  i.e.  closed  at  one  end  and  having  but  one 
door  for  charging  and  discharging ;  or  they  are  "  through  "  retorts, 
about  18  feet  long,  having  a  door  at  each  end,  so  that  they  may  be 
charged  or  emptied  from  either  side  of  the  furnace.  A  modified 
form  of  the  latter  is  the  "  inclined  "  retort,  set  at  an  incline  of  about 
32°,  the  coal  being  run  in  at  the  upper  end,  and  the  coke  discharged 
by  gravity,  by  opening  the  door  at  the  lower  end.  Each  bench  is 
heated  to  1000°  or  1200°  C.  by  a  coke  fire  on  a  grate  below  the  re- 
torts, or,  in  more  modern  plants,  by  generator  gas.  A  number  of 
benches  are  built  together,  and  constitute  a  "  stack." 

•From  the  front  of  each  retort  a  vertical  cast-iron  pipe  (B)  about 
6  inches  in  diameter,  and  called  the  "  stand-pipe,"  ascends  to  the 
top  of  the  bench,  where  it  joins  the  "bridge-"  and  "dip-pipes," 
which  conduct  the  volatile  products  from  the  retort  to  the  hydraulic 
main  (C).  This  is  a  long  covered  trough,  extending  the  entire 
length  of  the  stack,  and  receiving  the  gas  and  distillate  from  each 
retort.  In  it  the  greater  part  of  the  tar  and  oily  products  condense 
and  collect  under  the  water  which  is  kept  in  the  main  to  act  as  a 
seal  to  the  ends  of  the  dip-pipes,  to  prevent  the  gas  from  passing 
back  into  the  retort  when  the  latter  is  opened.  Ammonium  salts, 
such  as  sulphate,  sulphide,  and  carbonate,  are  washed  from  the  gas  as 
it  bubbles  through  the  water,  and  are  afterwards  recovered  (p.  125). 
The  ends  of  the  dip-pipes  must  not  extend  more  than  2  inches 
into  the  water ;  otherwise,  there  is  pressure  in  the  retort  and  con- 
sequent loss  from  leakage  and  from  deposition  of  carbon  in  the 
retort  and  stand-pipe.  If  the  gas  is  allowed  to  cool  in  contact 
with  the  tar,  the  latter  absorbs  some  of  the  illuminants,  thus  reduc- 
ing the  candle  power  (p.  276).  If  the  stand-pipes  are  too  hot,  the 
volatile  constituents  of  the  tar  are  driven  out,  and  a  very  thick  mass 
deposits,  causing  clogging. 

From  the  hydraulic  main  a  pipe  (not  shown)  leads  to  the  con- 
denser (D),  which  consists  of  a  series  of  vertical  cast-iron  pipes, 
connected  by  bends  at  the  top,  and  opening  at  the  bottom  into  an 
iron  box.  This  box  is  divided  by  transverse  partitions  which  do 
not  extend  to  the  bottom,  merely  dipping  into  the  ammoniacal  liquor 
and  tar  contained  in  it.  The  liquor  forms  a  seal,  thus  forcing  the 
gas  to  pass  through  the  pipes,  while  the  condensed  products  flow 
along  the  bottom  of  the  box  to  the  tar  well.  These  condensers  are 
simply  air  cooled,  but  certain  forms  are  constructed  with  water 
coolers.  In  those  most  frequently  in  use  in  this  country  the  pipes 
are  laid  at  a  very  slight  incline  to  the  horizontal. 


ILLUMINATING  GAS  271 

The  annular  condenser  consists  of  a  series  of  vertical  pipes  con- 
nected by  diagonal  pipes  leading  from  the  bottom  of  one  to  the  top 
of  the  next.  Through  each  of  these  vertical  pipes  a  smaller  tube 
passes  parallel  to  the  length  of  the  pipe  and  opening  to  the  air  at 
both  ends,  thus  forming  an  annular  space  in  each  pipe,  through 
which  the  gas  passes  dowmvard,  and  then  through  the  diagonal  pipe 
to  the  top  of  the  next.  In  this  way  a  very  large  air-cooled  surface 
is  obtained.  At  the  bottom  of  each  cooling  pipe  a  small  pipe  car- 
ries away  the  condensed  tar  and  liquor. 

The  tubular  condenser  consists  of  a  rectangular  box  about  2  feet 
wide  and  20  feet  high,  divided  into  narrow  sections  by  partitions 
extending  alternately  to  within  a  few  inches  of  the  top  and  of  the 
bottom.  Through  each  section,  a  number  of  narrow  horizontal  tubes, 
open  to  the  air  at  each  end,  extend  from  one  side  of  the  box  to  the 
other.  In  this  way  the  gas  passing  through  the  sections  is  exposed 
to  a  very  large  cooling  surface. 

Water  condensers  consist  essentially  of  pipes  surrounded  by  flow- 
ing water.  Through  these  the  gas  is  made  to  pass  in  a  direction 
opposite  to  that  in  which  the  water  flows.  By  regulating  the  supply 
of  water,  the  temperature  is  easily  controlled. 

The  object  of  the  condenser  is  to  cool  the  gas  slowly  to  the  tem- 
perature of  the  atmosphere,  provided  this  is  not  under  50°  C.  Cool- 
ing below  this  causes  condensation  of  somo  of  the  illuminants,  with 
corresponding  loss.  If  the  cooling  is  very  rapid,  the  tarry  matter 
separates  quickly,  and  drags  some  of  the  lighter  hydrocarbons  down 
with  it. 

The  exhauster  (E,  Fig.  69)  is  to  draw  the  gas  from  the  retort, 
through  the  hydraulic  main  and  condenser,  and  to  act  as  a  pump 
to  force  it  through  the  remaining  parts  of  the  plant.  By  drawing 
the  gas  out  of  the  retort  quickly  there  is  less  decomposition  of  the 
gas  itself,  and  hence  less  carbon  is  deposited  in  the  retort;  a  larger 
yield  results  and  less  fuel  is  necessary,  while  the  retort  lasts  longer. 

Another  form  of  exhauster  is  a  direct-acting  pump,  which  draws 
the  gas  from  the  retort  and  condenser,  and  forces  it  to  the  purifiers. 

Root's  rotary  exhauster  is  frequently  employed,  but  BeaPs 
(Fig.  70)  is  more  generally  used.  This  consists  of  an  outer  circular 
casing  having  inlet  and  outlet  pipes,  and  an  inner  revolving  drum 
(B),  which  turns  on  an  eccentric  axis  in  such  a  way  that  the  drum 
just  touches  the  lowest  point  of  the  inner  surface  of  the  casing. 
Through  slots  cut  in  the  drum,  two  blades  or  diaphragms  (D)  slide 
freely  over  one  another,  to  form  a  double  diaphragm,  variable  in 
width,  according  to  the  relative  position  of  the  blades  to  each  other. 


272  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

In  the  outer  end  of  each  blade  is  a  pin,  which  travels  in  a  circular 
groove  sunk  in  the  ends  of  the  casing.  Thus  as  the  drum  revolves 
about  its  axis,  the  pins,  travelling  in  the  fixed  groove,  draw  the 
blades  in  and  out,  across  the  axis  of  the  drum.  The  outer  ends  of 
the  blades  are  thus  always  kept  in  contact  with  the  walls  of  the 
casing.  The  exhauster  is  driven  by  an  engine,  and  the  rotary 
blades  and  drum  catch  the  gas  which  enters  through  the  inlet,  and 
force  it  out  through  the  other  pipe. 


FIG.  70.  FIG.  71. 


The  steam  jet  exhauster  (Fig.  71*)  is  very  effective,  but  heats  the 
gas,  which  is  afterwards  cooled  in  the  washer.  A  jet  of  steam  is 
blown  through  conical  openings  into  a  wide  pipe,  drawing  the  gas 
along  with  it  into  the  cones. 

The  tar  extractor  (F,  Fig.  69)  is  a  short  tower  filled  with  nu- 
merous horizontal  perforated  plates.  The  friction  of  the  gas  in  pass- 
ing through  the  small  holes  in  these  plates  removes  the  last  traces  of 
tar  and  prevents  clogging  in  the  scrubber.  In  Europe  the  apparatus 
of  Pelouze  and  Audouin  is  much  employed.  This  is  a  bell  made  up 
of  three  layers  of  wire  netting,  or  of  perforated  plates,  which  is  sus- 
pended in  a  water  seal.  The  gas  enters  under  the  bell  and  passes 
through  the  meshes  or  perforations  of  the  bell  walls,  to  which  the 
tar  particles  attach  themselves  and  finally  drop  to  the  bottom  and 
run  off  by  a  special  pipe. 

The  scrubber  and  washer  are  intended  to  remove  the  ammonia 
and  part  of  the  carbon  dioxide  and  hydrogen  sulphide.  In  the 
former  the  gas  is  brought  into  contact  with  thin  films  or  layers  of 
ammoniacal  liquor  from  the  hydraulic  main  or  condensers,  which 
trickles  over  coke,  twigs,  wooden  slats,  or  pebbles,  in  a  tower.  This 
liquor  absorbs  some  of  the  carbon  dioxide  and  hydrogen  sulphide, 
which  combine  with  the  ammonia.  In  tlie  washer  the  gas  is  brought 

*  After  Ost,  Lehrbuch  d.  tech.  Chemie. 


ILLUMINATING   GAS  273 

in  contact  with  pure  water,  trickling  over  twigs,  coke,  etc.,  and 
which  removes  the  ammonia  from  the  gas. 

Tower  scrubbers  are  tall  cast-iron  vessels  built  in  segments,  each 
of  which  has  a  "  grid "  or  grating,  upon  which  the  filling  material 
is  supported.  Two  towers  are  always  used  in  conjunction,  the  first 
fed  with  arnmoniacal  liquor  and  the  second  with  water.  The  amount 
of  liquor  and  water  is  very  carefully  regulated,  and  the  gas  entering 
at  the  bottom  of  the  first  tower  passes  up  and  then  to  the  bottom  of 
the  second,  and  is  thus  first  brought  into  contact  with  the  strongest 
liquor  and  finally  with  pure  water.  These  tower  scrubbers  are  now 
only  used  in  old  plants ;  in  all  modern  establishments  they  have  been 
replaced  by  scrubber-washer  machines. 

The  Standard  scrubber-washer  machine  (G,  Fig.  69)  is  a  Q-shaped 
iron  vessel,  divided  into  a  series  of  narrow  chambers  by  transverse 
partitions.  In  the  upper  half  of  the  apparatus  is  a  revolving  shaft 
carrying  a  number  of  thin  wooden  grids,  bolted  together  in  parallel 
segments,  with  blocks  making  a  space  of  about  one-eighth  of  an  inch 
between  each  pair  of  grids.  A  group  of  these  slats  revolve  in  each 
chamber.  Water  at  about  60°  F.  is  admitted  to  the  last  chamber  of 
the  series,  at  the  rate  of  about  one  gallon  for  each  1000  cubic  feet  of 
gas,  and,  automatically  regulated,  flows  from  chamber  to  chamber  in 
a  direction  opposite  to  that  in  which  the  gas  is  passed.  Thus  the 
fresh  water  comes  in  contact  with  the  most  nearly  purified  gas.  The 
level  of  the  water  is  lower  in  each  succeeding  chamber,  until  in  the 
first  chamber,  where  the  gas  enters  the  apparatus,  the  strong  ammo- 
niacal  liquor  is  only  a  few  inches  deep. 

By  the  revolution  of  the  shaft,  the  grids  are  submerged  in  the 
liquor,  and  freshly  wetted  surfaces  are  brought  into  the  upper  part 
of  the  apparatus.  By  a  suitable  arrangement  of  baffle  plates,  the 
gas  is  made  to  enter  each  chamber  at  the  centre,  and  find  its  way  to 
the  circumference  by  passing  through  the  narrow  spaces  between  the 
grids.  The  water,  forming  a  thin  film  on  them,  absorbs  the  ammo- 
nia, carbon  dioxide,  etc. ;  and  as  the  shaft  revolves  from  12  to  15 
times  per  minute,  the  solution  formed  is  at  once  mixed  with  the 
liquor  in  the  bottom  of  the  chamber.  The  machine  does  its  work 
very  effectively,  and  in  this  country  is  rapidly  replacing  the  tower 
scrubbers. 

From  the  scrubbers  the  gas  passes  to  the  purifiers  (H,  Fig.  69), 
whose  chief  purpose  is  to  remove  sulphur  compounds.  They  are 
shallow  rectangular  iron  boxes,  each  having  a  false  bottom,  upon 
which  the  purifying  material  rests.  The  gas  enters  under  this 
grating  and  leaves  by  a  pipe  opening  just  under  the  cover,  which 


274  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

rests  in  a  hydraulic  seal,  and  is  lifted  by  a  travelling  crane.  Usually 
four  purifiers  are  plaeed  in  a  series,  one  of  which  is  emptied  and 
recharged  at  a  time,  without  interrupting  the  purification  process. 
The  foul  gas  enters  the  most  nearly  exhausted  purifier,  and,  passing 
through  the  others,  leaves  the  apparatus  through  that  most  recently 
charged,  connection  being  made  between  the  purifiers  by  means  of 
a  complicated  piece  of  apparatus  (L  and  0,  Fig.  69)  called  the 
centre  seal. 

The  purifying  materials  may  be  slaked  lime  or  hydrated  ferric 
oxide.  Lime  is  the  oldest  material  used  and  is  also  the  best,  since 
it  removes  both  the  carbon  dioxide  and  carbon  disulphide.  But  it  is 
expensive,  and  the  spent  lime,  having  a  most  offensive  odor  and  con- 
siderable bulk,  is  difficult  to  dispose  of.  The  lime  should  be  thor- 
oughly slaked  several  days  before  use,  and  should  contain  as  much 
water  as  it  will  hold  without  becoming  pasty  or  liquid.  It  is  placed 
in  the  purifiers  in  layers  about  six  inches  deep.  The  reactions  occur- 
ring with  lime  are  :  — 

1)  Ca(OH)2  +  2  H2S  =  Ca(SH)2  +  2  H20. 

2)  Ca(OH)2  +  H2S  =  CaS  +  2H20. 

3)  CaS  +  CS2  =  CaCS3  ,  (calcium  thiocarbonate). 

4)  Ca(OH)2  +'C02  =  CaC03  +  H20. 

Since  carbon  dioxide  will  decompose  calcium  sulphide,  sulphy- 
drate,  or  thiocarbonate,  if  gas  containing  it  is  passed  through  a  foul 
purifier,  the  following  is  liable  to  take  place  :  — 

CaS  +  C02  +  H20  =  CaC03  +H2S. 

CaCS3  +  C02  +  H20  =  CaC03  +  CS2  +  H2S. 

The  volatile  sulphides  thus  liberated  must  be  removed  in  a  second 
purifier,  into  which  no  carbon  dioxide  enters.  Carbon  dioxide  has  a 
very  deleterious  effect  on  the  illuminating  power  of  the  gas. 

When  iron  oxide  is  used,  only  the  hydrogen  sulphide  is  removed 
from  the  gas  :  — 


2)   Fe203  •  3  H20  +  3  H20  +  3  H2S  =  Fe2S3  +  6  H20. 

The  oxide  is  a  natural  bog  iron  ore,  Fe203  •  3  H2O.  When  fresh 
it  contains  about  50  per  cent,  water  and  a  large  amount  of  vegetable 
matter,  but  before  use  it  is  dried  until  about  one-half  of  the  moisture 
is  expelled,  and  is  then  mixed  with  an  equal  bulk  of  sawdust  to  ren- 


ILLUMINATING  GAS  275 

der  it  more  porous.  When  it  becomes  inactive  through  absorption  of 
sulphur,  it  is  "revivified"  by  removing  it  from  the  purifier  and 
spreading  it  in  a  layer  a  foot  or  more  in  depth,  where  the  air  can 
act  upon  it.  Considerable  heat  is  evolved  by  the  action  of  the  oxy- 
gen of  the  air  on  the  iron  sulphides  :  — 


FeaS3  +  30  =  Fe  A  +  3  S. 

Thus  free  sulphur  is  deposited  in  the  oxide.  The  ore  may  be  revivi- 
fied repeatedly  until  the  free  sulphur  accumulates  in  it  to  the  amount 
of  50  or  55  per  cent,  when  the  proper  action  in  the  purifiers  is  hin- 
dered, and  fresh  oxide  must  be  used.  If  some  air  is  admitted  along 
with  the  gas,  the  iron  oxide  is  revivified  in  the  purifiers,  and  need 
not  be  removed  so  often  ;  but  this  dilutes  the  gas  slightly  with  nitro- 
gen. One  ton  of  good  iron  oxide  will  purify  about  one  and  a  quarter 
million  cubic  feet  of  gas. 

Sometimes  lime  is  used  before  the  iron  oxide,  in  order  to  remove 
carbon  dioxide.  Any  sulphur  compounds  of  the  lime  which  may  be 
formed  are  decomposed  by  the  carbon  dioxide  in  the  foul  gas  (see 
above).  A  considerable  amount  of  carbon  dioxide  is  present  in  un- 
purified  water  gas,  and  is  generally  thus  removed  before  the  gas 
enters  the  iron  oxide  purifiers. 

The  purified  gas  passes  through  the  station  meter  (I,  Fig.  69) 
and  then  to  the  holder  (J),  from  which  it  is  delivered  to  the  street 
mains. 

The  usual  impurities  found  in  gas  are  ammonia,  hydrogen  sul- 
phide, and  carbon  dioxide.  Ammonia  is  detected  by  holding  a  strip 
of  wet  turmeric  or  litmus  paper  in  a  stream  of  the  gas  ;  the  former 
becomes  brown  or  red,  and  the  latter  blue.  For  hydrogen  sul- 
phide, paper  wet  in  lead  acetate  or  silver  nitrate  is  used.  Carbon 
dioxide  is  detected  by  shaking  a  small  bottle  of  the  gas,  freed  from 
hydrogen  sulphide,  with  lime  or  baryta  water. 

The  yield  from  one  ton  of  good  gas  coal  is  approximately  :  — 

10,000  cu.  ft.  16  candle  power  gas. 

1400  pounds  coke. 

120  pounds  tar. 

20  gallons  ammoniacal  liquor  (10  to  12  oz.). 

When  the  ammoniacal  liquors  from  the  hydraulic  main,  con- 
densers and  scrubbers  are  mixed,  the  "gas  liquor"  thus  formed 
is  of  approximately  "10  ounce"  strength,  i.e.  the  ammonia  gas 
which  can  be  liberated  from  one  gallon  of  the  liquor  will  completely 


276  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

neutralize  10  ounces  by  weight  of  real  sulphuric  acid.  It  is  used  for 
the  production  of  ammonia  (p.  124).  The  tar  is  pumped  from  the 
tar  well  into  barrels  or  tanks  for  shipment  to  the  tar  distiller 
(p.  279). 

The  illuminating  power  of  gas  is  expressed  in  "candles,"  by 
which  is  meant  the  ratio  of  its  illuminating  power  to  that  of  a 
"standard  candle,"  as  measured  by  a  photometer.  The  English 
standard  is  the  light  of  a  sperm  candle,  weighing  one-sixth  of  a 
pound,  when  burning  120  grains  per  hour.  But  this  is  subject  to 
variation,  and  much  ingenuity  has  been  expended  in  devising  a 
better  standard.  A  burner  designed  for  use  with  a  mixture  of  air 
and  pentane,  C5H12,  has  found  some  favor  in  Europe.  In  Germany 
the  light  of  a  lamp  burning  amyl  acetate,  with  a  specified  height  of 
flame  and  size  of  wick,  is  the  official  standard.  In  this  country 
standard  candles  are  used.  When  testing  gas,  it  is  customary  to 
burn  it  at  the  rate  of  5  cu.  ft.  per  hour,  in  a  burner  of  the  argand 
type.  Ordinary  coal  gas  is  generally  about  16  candle  power,  but  it 
is  now  frequently  the  practice  to  "enrich"  it  by  putting  into  the 
retort,  along  with  each  charge  of  coal,  an  iron  cylinder  containing 
petroleum  oil.  This  is  closed  with  a  cork,  which  soon  burns  out,  and 
the  oil  escapes  and  is  decomposed,  the  vapors  mixing  with  the  coal 
gas,  thus  increasing  its  illuminating  power.  • 

A  recent  improvement  in  gas  lighting  is  the  introduction  of 
incandescent  burners,  in  which  the  non-luminous  flame  of  a  Bunsen 
burner  is  made  to  heat  a  mantle  or  gauze  composed  of  the  oxides  of 
various  rare  earths,  especially  thorium  and  cerium.  The  mantle 
being  raised  to  incandescence,  glows  with  a  powerful  light,  while 
very  little  heat  is  given  out.  The  consumption  of  gas  in  these 
burners  is  usually  about  three  and  one-half  feet  per  hour,  and  their 
efficiency  is  about  four  times  that  of  an  ordinary  argand  burner. 
They  are  advantageous  to  use  with  a  gas  of  low  illuminating  power, 
provided  it  has  considerable  heating  value. 

Oil  gas  is  now  largely  made  by  "  cracking  "  certain  petroleum,  tar, 
or  shale  oils  in  retorts.  In  Pintsch's  process  the  retort  is  divided 
by  a  transverse  partition  into  an  upper  and  a  lower  chamber.  The 
oil  is  cracked  and  vaporized  in  the  upper  chamber,  and  the  vapors 
pass  into  the  lower  compartment,  whic.h  is  heated  to  nearly  1000°  C., 
where  the  vapors  are  "fixed"  and  form  permanent  gases.  In 
Peebles'  process  the  retorts  are  not  heated  so  hot,  and  the  oil  is 
partly  cracked  and  partly  distilled  and  fractionated,  so  that  only 
very  volatile  hydrocarbons  leave  the  apparatus ;  the  heavier  oils  are 
condensed  and  returned  to  the  retort.  The  gas  is  then  purified  and 


ILLUMINATING  GAS  277 

used  to  enrich  other  gases,  or  is  burned  alone,  or  with  air.  Oil  gas 
has  a  very  high  candle  power,  usually  over  50.  That  made  by  the 
Pintsch  process  is  extensively  used  in  the  pure  state  for  lighting 
railroad  cars.  It  is  compressed  into  cylinders  for  carriage,  but  the 
pressure  must  be  low ;  otherwise  great  loss  of  illuminating  power 
occurs,  owing  to  the  condensation  of  the  heavy  illurainants.  It  can 
only  be  burned  in  special  forms  of  burners,  otherwise  it  is  very 
liable  to  smoke  or  deposit  soot.  It  is  rich  in  benzene  and  olefine 
hydrocarbons.  By  mixing  with  a  certain  amount  of  pure  oxygen 
the  combustion  and  illuminating  power  can  be  greatly  improved. 
Acetylene  has  recently  become  prominent  as  a  possible  future 
illuiniiiant.  By  heating  a  mixture  of  coke  powder  and  lime  in  an 
electric  furnace,  calcium  carbide  is  produced.  When  treated  with 
water  this  is  decomposed,  with  formation  of  acetylene :  — 

CaC2  +  2  H20  =  Ca(OH)2  +  C2H2. 

It  burns  readily  with  separation  of  carbon,  which  is  heated  to  incan- 
descence in  the  flame,  and  gives  the  gas  a  high  illuminating  value. 
But  it  cannot  be  used  successfully  to  enrich  coal  or  water  gas,  since 
its  candle  power  is  very  much  lowered  by  mixing  with  other  gases. 
When  burned  in  a  special  form  of  burner,  under  high  pressure,  it 
yields  a  very  brilliant  light.  It  has  some  action  on  copper  and  brass, 
and  under  certain  conditions  might  attack  the  brass  valves  and 
stop-cocks  employed  in  gas  fitting,  and  form  a  highly  explosive  body. 

One  ton  of  calcium  carbide  of  80  per  cent  purity  will  produce 
about  1000  cu.  ft.  of  acetylene  gas,  and  it  has  been  proposed  to 
employ  it  in  small  generators  for  illuminating  purposes.  But  the 
present  cost  of  calcium  carbide  is  prohibitory  to  any  extended  use  of 
acetylene. 

Air  gas,  so  called,  is  produced  by  causing  air  to  pass  through 
layers  of  the  very  volatile  petroleum  distillates,  having  densities 
from  80  to  90  Be.  The  air,  together  with  sufficient  vapor  to  form  a 
combustible  mixture,  is  led  directly  into  the  burner,  since  it  cannot 
be  piped  any  considerable  distance  without  condensation  of  the 
illuminants.  The  rate  of  flow  of  air  through  the  apparatus  must  be 
very  exactly  regulated.  Air  gas  is  much  used  when  other  gas  is  not 
available. 

In  some  parts  of  Europe,  where  coal  is  very  expensive,  gas  is 
made  by  distilling  artificially  dried  peat.  The  gas  contains  more 
carbon  dioxide  than  coal  gas,  and  more  lime  is  needed  for  purifica- 
tion. It  is  about  18  candle  power,  and  considerable  tar  and  ammo- 
niacal  liquor  is  also  obtained. 


278 


OUTLINES  OF  INDUSTRIAL  CHEMISTRY 


The  average  composition  of  different  varieties  of  gas  is  shown  in 
the  following  table  :  *  — 

ANALYSES. 


COAL. 

WATER  (CARBUEETTED). 

WATER  (FUEL). 

OIL. 

Candle  power  .     . 

17.5 

25.0 



65.0 

Ilium  inants      .     . 

5.0 

16.6 

— 

45.0 

Marsh  Gas  .     .     . 

34.5 

19.8 

1.0 

38.8 

Hydrogen   .     .     . 

49.0 

32.1 

52.0 

14.6  Ethane 

Carbonic  Oxide    . 

7.2 

26.1 

38.0 

— 

Nitrogen      .     .     . 

3.2 

2.4 

3.0 

1.1 

Oxygen  .... 

— 

.     — 

— 

— 

Carbonic  Acid 

1.1 

3.0 

6.0 

— 

REFERENCES 

Practical  Treatise  on  the  Manufacture  and  Distribution  of  Coal  Gas.     Samuel 

Clegg,  London,  1859. 

Traits'  theoretique  et  pratique  de  la  Fabrication  du  Gaz.     E.  Borias,  Paris,  1890. 
Manufacture  of  Gas  from  Tar,  Oil,  etc.     W.  Burns,  New  York,  1887. 
Practical  Treatise  on  the  Manufacture  of  Coal  Gas.     W.  Richards,  London. 
Fabrikation  der  Leuchtgase.     G.  Thenius,  Leipzig,  1891. 

The  Chemistry  of  Illuminating  Gas.     N.  H.  Humphreys,  London,  1891.     (King.) 
The  Chemistry   of  Gas   Manufacture.     W.  J.    A.  Butterfield,   London,   1896. 

(Griffin  and  Co.) 
A  Textbook  of  Gas  Manufacture.     John  Hornby,  London,  1896.     (Bell  and 

Sons.) 

A  Treatise  on  Gas  Manufacture.     W.  King.     (King.) 
Gas  Engineer's  Handbook.     T.  Newbiggin,  London,  1889.     (King.) 
Handbuch  ftir  Gas-Beleuchtung.     E.  Schilling,  1892. 
Journal  of  Gas  Lighting.     London. 

Vols.  59,  60,  61,  62,  and  others.     (Coal  Gas.) 


COAL-TAR 

The  tar  collected  from  the  hydraulic  main  and  condensers  of  the 
gas  works  is  a  black,  oily,  foul-smelling  liquid  averaging  1.15  sp.  gr. 
Its  composition  is  exceedingly  complex,  and  it  is  always  mixed  with 
some  of  the  gas  liquor,  while  it  retains  in  solution  several  of  the 
constituents  of  the  illuminating  gas. 

In  the  early  days  of  "gas  making,  the  tar  accumulated  in  large 

*  C.  D.  Jenkins.    Reports  of  the  Mass.  State  Gas  Inspectors. 


COAL-TAR  279 

quantities,  and  no  use  being  known  for  it,  became  a  great  nuisance. 
But  the  discovery  of  several  important  substances  in  distillates  from 
it  has  given  rise  to  great  industries. 

Coal-tar  is  used  to  some  extent  without  treatment  for  preserving 
timber,  making  "  tar  paper,"  as  a  protective  paint  and  cement  for 
acid  pipes  and  condensing  vessels,  and  in  forming  certain  furnace 
linings.  But  nearly  all  the  tar  now  produced  is  subjected  to  frac- 
tional distillation  for  the  separation  of  the  more  important  constitu- 
ents. These  may  be  considered  in  three  general  classes :  (a),  the 
hydrocarbons,  the  most  valuable,  are  bodies  of  a  neutral  character, 
not  affected  by  dilute  acids  nor  alkali ;  (6),  the  phenols,  bodies  of  a 
weak  acid  character,  and  containing  oxygen ;  (c),  the  bases,  which 
contain  nitrogen,  and  are  generally  present  in  such  small  amounts 
that  they  are  not  recovered.  The  method  of  distillation  varies  con- 
siderably as  the  market  price  of  the  distillates  fluctuates,  and  accord- 
ing to  the  composition  of  the  tar  received  from  different  gas  works. 
If  benzenes  are  low  in  price,  the  light  oils  are  collected  together.  As 
a  rule,  the  phenols  are  not  all  separated,  since  the  demand  for  them 
is  not  very  great.  Some  tars  are  distilled  only  until  the  light  oils 
are  removed,  and  the  residue  employed  for  asphalt.  But  when 
anthracene  is  present,  the  distillation  is  carried  on  until  the  heavy 
oils  are  removed,  and  the  residue  is  sold  as  pitch. 

When  received  from  the  gas  works,  the  tar  is  run  into  a  tank 
above  the  level  of  the  still,  or  into  a  brick-lined  cistern  sunk  in  the 
ground,  and  is  allowed  to  stand  until  the  ammoniacal  liquor  mixed 
with  it  has  separated  by  gravity.  To  facilitate  this  the  tar  is  some- 
times warmed  by  a  steam  coil  in  the  tank,  especially  in  cold  weather. 
Since  the  gas  liquor  causes  frothing  in  the  still,  it  is  removed  as 
completely  as  possible,  and  sent  to  the  ammonia  distiller. 

In  the  early  days  of  the  industry  old  boilers  were  frequently 
employed  as  stills,  but  in  modern  works  the  stills  are  especially  con- 
structed for  the  purpose.  They  are  sometimes  horizontal  cylindri- 
cal vessels,  having  a  capacity  of  from  15  to  25  tons,  and,  in  some 
cases  provided  with  two  or  more  still-heads.  But  a  better  form  is 
a  vertical  cylinder  made  of  wrought-iron  or  steel  plates  from  three- 
eighths  to  one-half  of  an  inch  thick;  the  diameter  is  equal  to  the 
height,  and  the  bottom  is  concave.  The  top  is  a  cast-iron  dome,  pro- 
vided with  a  manhole,  an  inlet  pipe  for  the  tar,  a  broad,  curved  out- 
let pipe  ("goose-neck")  for  the  vapors,  and  a  small  overflow  pipe 
("tell-tale").  Sometimes  there  is  a  safety-valve  and  thermometer 
tube ;  if  the  former  is  omitted,  the  manhole  cover  is  not  screwed 
down,  but  closes  the  opening  by  its  own  weight ;  should  excessive 


280  OUTLINES   OF  INDUSTRIAL   CHEMISTRY 

pressure  develop  within  the  still,  the  cover  is  lifted  and  the  vapors 
escape.  The  arched  bottom  rises  to  a  considerable  height,  thus  dis- 
tributing t?ie  heat  into  the  interior  of  the  mass  of  tar,  and  the  outlet 
pipe  being  placed  at  the  lowest  point,  it  is  also  of  assistance  in 
emptying  the  still.  The  bottom  is  sometimes  protected  from  direct 
contact  with  the  flame  by  a  brick  arch  (curtain  arch).  There  is 
usually  a  coil  in  the  still,  through  which  superheated  steam  is  blown, 
towards  the  end  of  the  process,  to  assist  in  the  distillation  of  the 
heavy  oils. 

These  upright  stills  are  set  in  furnaces  so  that  the  flames  play 
under  the  bottoms,  and  about  half  way  up  the  height,  through  side 
flues  in  the  brick  setting.  They  vary  much  in  size ;  in  England  they 
are  from  10  to  20  tons  capacity;  in  Germany  larger  ones  are  used. 

The  condenser  consists  of  a  cast-  or  wrought-iron  or  lead  worm, 
placed  in  a  tank  of  water.  A  steam  pipe  is  arranged  to  warm  the 
water,  if  necessary. 

While  the  still  is  yet  hot  from  the  previous  distillation,  the  tar 
is  run  in.  Since  the  large  mass  of  cold  tar  requires  some  time  for 
heating,  the  fire  is  started  when  the  still  is  half  full.  When  the  tar 
runs  from  the  tell-tale  pipe,  the  manhole  and  valves  are  closed,  and 
the  heat  raised  until  the  contents  begin  to  froth.  The  overflow 
pipe  is  then  opened,  and  any  ammoniacal  liquor  which  has  separated 
is  drawn  off.  The  heating  is  continued  carefully  until  the  still-head 
gets  warm,  and  puffs  of  vapor,  and  finally  drops  of  liquid,  begin  to 
come  from  the  condenser.  The  fire  is  then  moderated,  in  order  to 
prevent  boiling  over.  A  closed  receiver  is  placed  at  the  end  of  the 
condenser,  and  the  distillation  is  continued  very  slowly,  until  the 
temperature  reaches  105°  C.,  when,  as  a  rule,  the  first  receiver  is 
changed.  The  distillate  is  commonly  separated  as  follows  :  — 

First  runnings,  or  "first  light  oil,"  to  105° C. 

Light  oil,  to  210°  C. 

Carbolic  oil,  to  230°  C. 

Creosote  oil,  to  270°  C. 

Anthracene  oil,  "  green  oil,"  above  270°  C. 

Sometimes  the  first  runnings  and  light  oil  are  collected  together 
until  the  temperature  reaches  170°  C. ;  and  the  distillate  between 
170°  C.  and  230°  C.  is  taken  as  carbolic  oil.  The  temperature  at 
which  the  distillation  is  stopped  depends  upon  the  quantity  of 
anthracene  in  the  distillate  and  upon  whether  it  is  desired  to  pro- 
duce hard  or  soft  pitch. 

The  first  runnings,  or  first  light  oil,  contain  water,  ammonium 


COAL-TAR  281 

salts,  the  very  volatile  oils,  and  a  small  quantity  of  heavier  oils  car- 
ried over  mechanically.  After  this  distillate  has  run  for  some  time, 
it  nearly  ceases,  although  the  fire  is  now  increased.  This  is  known 
as  the  "break,"  and  is  the  point  where  the  receiver  is  generally 
changed.  During  the  interval  a  peculiar  sputtering  noise  ("rattles") 
is  heard  in  the  still,  caused  by  drops  of  condensed  water  falling  into 
the  tar,  which  is  now  considerably  above  110°  C. 

When  the  liquid  begins  to  run  from  the  condenser  again,  the 
"second  light  oil"  is  collected  until  the  temperature  of  the  tar 
reaches  210°  C.,  or  until  the  distillate  equals  1.000  sp.  gr.  This  is 
shown  by  catching  some  of  it  in  a  glass  of  water;  if  it  forms  spheri- 
cal drops  which  neither  sink  nor  rise  in  the  water,  but  float  at  what- 
ever point  they  happen  to  fall,  the  receiver  should  be  changed. 
During  this  period  very  little  cooling  water  is  admitted  to  the  con- 
denser, so  that  it  is  warmed  to  40°-50°  C. ;  the  water  is  then  cut  off 
entirely. 

The  carbolic  oil  is  distilled  until  the  temperature  of  the  tar 
reaches  240°  C.,  or  until  a  few  drops  of  the  distillate  cooled  on  an 
iron  plate  show  crystals,  of  naphthalene.  This  oil  contains  phenols, 
and  as  the  naphthalene  is  less  soluble  in  the  heavy  oils  than  in  the 
phenols,  its  crystallization  indicates  that  all  the  latter  have  distilled 
off.  The  warm  water  in  the  condenser  prevents  crystallization  in 
the  worm ;  towards  the  end  of  this  period  it  is  sometimes  necessary 
to  heat  the  water  by  a  steam  coil. 

The  receiver  is  again  changed,  and  the  "  creosote  oil "  collected 
until  the  temperature  reaches  270°  C.  The  first  runnings  of  this 
contain  much  naphthalene,  but  later  the  quantity  present  is  small, 
and  remains  dissolved  in  the  heavy  oil.  This  distillate  is  the  least 
valuable  and  is  often  not  purified  further. 

The  anthracene  oil,  or  "green  oil,"  collected  over  270° C.,  con- 
tains anthracene,  the  most  valuable  constituent  of  the  tar.  The 
water  in  the  condenser  is  now  brought  to  the  boiling  point.  Super- 
heated steam  is  injected  into  the  hot  tar  in  the  still  to  aid  in  carry- 
ing over  the  heavy  vapors.  The  process  is  generally  stopped  when 
the  distillate  becomes  "  gummy  " ;  on  cooling  it  has  about  the  con- 
sistency of  butter. 

The  pitch  left  in  the  still  is  a  thick,  viscous  mass  while  hot,  and 
if  run  out  immediately  will  take  fire  in  the  air.  After  cooling  a 
few  hours,  it  is  run  out  through  the  pitch  cock,  and,  when  cold, 
hardens  and  is  sold  as  "  hard  pitch."  But  the  still  must  be  emptied 
while  the  pitch  is  warm  enough  to  drain  out  completely,  for  if  any 
is  left  in  the  still  the  heat  radiating  from  the  brickwork  will  con- 


282  OUTLINES  OF   INDUSTRIAL  CHEMISTRY 

vert  it  into  coke,  which  fastens  very  firmly  to  the  still  bottom  and 
does  not  dissolve  when  a  fresh  charge  of  tar  is  run  in.  To  facilitate 
emptying,  and  also  to  supply  a  demand  for  "  soft  pitch,"  it  is  often 
the  practice,  after  the  anthracene  oil  is  distilled,  to  pump  into  the 
still  a  certain  amount  of  creosote  or  carbolic  oil,  or  the  "  dead  oils  " 
from  which  the  anthracene  has  been  extracted.  This  mixes  with  the 
hot  tar  and  produces  a  pitch  of  any  desired  consistency,  according 
to  the  quantity  of  oil  used. 

Stills  are  sometimes  provided  with  mechanical  stirring  apparatus 
to  prevent  the  pitch  from  burning  on  the  bottom,  and  to  assist  in 
mixing  it  with  the  oils  used  for  softening  it. 

The  crude  distillates  obtained  directly  from  the  tar  are  further 
purified  and  separated  into  commercial  products.  The  first  runnings 
contain  ammoniacal  liquor  and  naphtha,  which  are  usually  separated 
by  gravity.  The  former  is  put  with  the  gas  liquor  from  the  tar ; 
the  latter  is  usually  refined  with  the  light  oil  distillate. 

The  light  oil  contains  benzene,  toluene,  and  xylene,  with  some 
thiophene,  phenols,  pyridine  bases,  and  heavy  oils.  It  is  distilled  in 
stills  much  like  those  used  for  tar,  but  smaller.  Two  fractions 
are  made,  naphtha,  which  distills  under  170°  C.,  being  further 
purified ;  and  the  last  runnings,  which  are  put  with  the  carbolic 
oil. 

The  naphtha  is  put  into  a  lead-lined  vessel  provided  with  an  agi- 
tator, and  thoroughly  mixed  with  dilute  caustic  soda  solution.  This 
combines  with  the  phenols,  which  are  thus  removed  when  the  soda 
solution  is  drawn  oft'.  After  washing  the  oil  with  water,  about  5  per 
cent  of  sulphuric  acid  (sp.  gr.  1.83)  is  added  and  agitated  with  the 
oil,  the  temperature  being  kept  low.  This  dissolves  thiophene,  un- 
saturated  hydrocarbons  and  pyridines,  and  chars  and  destroys  other 
matter.  The  acid  tar  thus  formed  is  drawn  off  and  the  oil  washed 
several  times  with  water,  and  finally  with  caustic  soda  to  remove  all 
the  acid.  The  washed  oil  is  then  redistilled.  When  collected  up  to 
110°  C.,  the  distillate  is  called  "90  per  cent  benzol,"  since  that 
amount  by  volume  distills  below  100°  C.  It  contains  about  70  per 
cent  pure  benzene,  24  per  cent  toluene,  and  some  xylene.  If  col- 
lected up  to  140°  C.,  the  distillate  is  known  as  "  50  per  cent  benzol," 
and  contains  about  46  per  cent  pure  benzene.  Between  140°  C.  and 
170° C.  a  distillate  called  "solvent  naphtha"  or  "benzine"  is  ob- 
tained. This  consists  mainly  of  xylenes,  cumenes,  etc.,  and  is  used 
as  a  solvent  for  resins  and  rubber,  and  to  wash  the  crude  anthracene 
obtained  from  the  anthracene  oil.  It  is  also  employed  to  enrich 
illuminating  gas,  and  as  a  cleansing  agent  for  grease-stained  fabrics. 


COAL-TAR  283 

It  must  not  be  confused  with  petroleum  benzine  (p.  292),  which  is  of 
different  composition. 

The  crude  50  or  90  per  cent  benzol  is  chiefly  employed  in  the 
coal-tar  dye  industry.  By  careful  distillation  in  a  rectifying  still, 
such  as  Coupier's  or  Sevalle's  (pp.  8,  9),  it  yields  pure  benzene, 
boiling  at  80-82°  C.,  toluene  at  110-112°  C.,  and  xylene,  137-143°  C. 

The  carbolic  oil  contains  phenols  and  naphthalene ;  after  cooling, 
the  oil  is  pressed  or  filtered  out  of  the  magma  of  crude  naphthalene 
crystals,  which  are  purified  by  treating  with  sulphuric  acid  and 
heating  to  destroy  the  phenol  left  in  them.  After  separating  the 
acid  tar  and  washing,  the  naphthalene  is  distilled  or  sublimed 
(p.  10). 

The  oil  pressed  from  the  naphthalene  crystals  may  be  treated  by 
either  of  the  following  processes  to  recover  the  phenols:  (a)  The 
oil  is  agitated  with  dilute  caustic  soda,  which  dissolves  the  phenols, 
forming  a  solution  of  "  sodium  carbolate."  This  separates  by  gravity 
from  the  undissolved  neutral  oils  and  is  drawn  off  and  decomposed 
with  sulphuric  acid,  whereby  crude  carbolic  acid  (phenol),  separates 
as  an  oily  liquid,  (b)  The  oil  may  be  heated  with  a  mixture  of  lime 
and  sodium  sulphate,  sodium  carbolate  being  formed  and  calcium 
sulphate  precipitating.  After  the  impurities  have  settled,  the  solu- 
tion of  phenols  (tar  acids)  is  decanted  and  sold  as  crude  carbolic  acid. 
This  is  purified  by  repeated  distillation  in  a  column  apparatus  of 
iron  or  copper,  with  zinc  condensers.  Sometimes  potassium  bichro- 
mate and  sulphuric  acid  are  put  into  the  still  to  oxidize  the  impuri- 
ties. Crystals  of  phenol  separate  from  the  distillate  on  cooling, 
while  the  cresols  remain  liquid.  The  phenol  is  separated  from  all 
liquid  matter  by  a  centrifugal  machine.  By  treating  the  alkaline 
solution  of  phenols  with  an  insufficient  quantity  of  acid,  the  cresols 
are  precipitated  first  and  may  be  separated,  the  phenol  being  sepa- 
rated afterwards  with  more  acid. 

Crystallized  phenol,  C6H6OH,  melts  at  42°  C.,  but  the  presence  of 
a  very  little  water  causes  the  whole  mass  to  liquify.  It  boils  at 
184°  C.,  and  can  be  distilled  unchanged.  Carbolic  acid  is  a  violent 
poison  and  has  a  very  penetrating  odor.  It  is  a  powerful  antiseptic, 
germicide,  and  disinfectant.  It  is  the  source  from  which  many  dyes, 
explosives,  and  medicinal  chemicals  are  prepared.  When  dissolved 
in  soap,  the  crude  tar  acids  are  often  used  as  antiseptics  under  the 
names  lysol  and  kreolin ;  these  are  soluble  in  water  or  emulsify 
with  it. 

The  creosote  oil  also  furnishes  naphthalene,  which  crystallizes  on 
cooling.  It  is  filtered,  or  pressed  in  presses  which  have  steam-heated 


284  OUTLINES  OF   INDUSTRIAL   CHEMISTRY 

plates;  the  crude  naphllial en e  is  washed  with  caustic  soda  solution 
and  with  concentrated  acid,  and  is  distilled  or  sublimed.  The  oil 
contains  cresols  and  higher  phenols,  naphthol,  and  liquid  paraffine, 
which  have  but  little  value  and  are  not  separated.  It  is  chiefly  used 
for  preserving  ("pickling")  timber  and  railroad  sleepers.  The 
timber  is  thoroughly  dried,  placed  in  tanks  from  which  the  air  is 
exhausted,  and  the  hot  creosote  oil  pumped  in  under  heavy  pres- 
sure. A  small  amount  is  used  for  lubricant,  and  as  an  illuminant 
for  outdoor  work  where  smoke  is  of  no  consequence.  It  is 
also  used  as  fuel,  and  extensively  in  the  preparation  of  "  sheep 
dips,"  liquids  used  for  destroying  ticks  and  vermin  on  sheep  and 
cattle. 

Naphthalene  is  one  of  the  most  important  constituents  of  coal-tar, 
forming  over  5  per  cent  of  it.  It  forms  shining  white  plate-like 
crystals,  which  melt  at  79°  C.,  and  boil  at  218°  C.  It  has  a  peculiar 
penetrating  odor,  and  is  much  used  instead  of  camphor  to  protect 
woollen  goods  and  furs  from  moths ;  it  is  also  used  to  prepare 
naphthols,  naphtylamines,  and  phthalic  acids  for  the  manufacture  of 
dyes.  Nitron aphthalene  is  employed  to  remove  the  "bloom"  from 
mineral  oils  (p.  294). 

The  anthracene  oil,  or  "green  oil,"  contains  about  10  per  cent 
anthracene,  C14H10,  together  with  other  solid  hydrocarbons,  such  as  phe- 
nanthrene,  chrysen,  carbazol,  paraffine,  and  liquid  oils  of  high  boiling 
points.  The  mass  is  cooled  until  the  solid  matter  has  crystallized, 
when  the  liquid  oils  are  removed  by  bag  filtering  or  by  a  filter  press 
or  centrifugal  machine.  The  crystalline  mass  so  obtained  is  pressed 
in  canvas  bags  in  a  hydraulic  press  at  a  temperature  of  40°  C.  The 
oils  expressed  are  then  again  chilled  to  a  low  temperature  and 
pressed,  or  are  redistilled  to  recover  more  anthracene;  then  they 
are  mixed  with  the  creosote  oil  or  run  back  into  the  tar  still  to  soften 
the  pitch.  The  crude  30  per  cent  anthracene  from  the  press  is 
pulverized  and  washed  with  creosote  oil  or  with  solvent  naphtha  from 
the  light  oils,  which  dissolves  much  of  the  contaminating  substances, 
but  does  not  remove  carbazol.  The  magma  is  again  "  centriffed  "  or 
pressed,  and  the  liquid  separated  is  distilled  to  recover  the  naphtha, 
while  the  residue  of  .phenanthrene,  which  has  no  special  value,  is 
usually  burned  for  lampblack. 

By  these  washings,  the  anthracene  is  raised  to  about  50  per  cent, 
when  it  is  sold  to  the  alizarine  manufacturer.  For  further  purifica- 
tion, it  is  washed  with  caustic  potash  to  remove  carbazol,  and  then 
it  is  sublimed  in  an  atmosphere  of  superheated  steam.  It  forms 
white  plates  of  pearly  lustre,  melting  at  213°  C.  and  boiling  at 


MINERAL  OILS  285 

;>60°C.  It  is  employed  entirely  in  the  preparation  of  artificial 
alizarine. 

The  pitch  left  in  the  still  after  the  distillation  is  either  hard  or 
soft,  as  described  on  page  281.  If  so  soft  that  it  remains  liquid  when 
cold,  it  is  often  used  as  a  black  varnish  for  painting  metal  work  and 
wood,  or  for  making  tarred  paper  or  roofing  paper.  Medium  soft 
pitch  is  used  as  a  cement  in  preparing  "  briquettes  "  from  coal  dust 
for  fuel.  Pitch  is  also  mixed  with  asphalt  for  making  sidewalks 
and  pavements. 

Soft  pitch  softens  at  about  38°-40°  C.  and  melts  at  60°  C.  When 
a  small  piece  is  chewed,  it  coheres  together  like  gum.  Hard  pitch 
softens  at  75°-SO°C.,  and  melts  above  120°  C.  When  chewed,  it 
pulverizes  into  a  non-cohesive  powder  in  the  mouth. 

REFERENCES 

Coal-Tar  and  Ammonia.  Geo.  Lunge,  London,  1887.  (Gurney  and  Jackson.) 
Die  Chemie  des  Steinkohlentheers.  Gustav  Schultz,  Braunschweig,  1890. 

(Vie\veg.) 

Die  Technische  Verwerthung  des  Steinkohlentheers.  G.  Thenius,  Vienna,  1887. 
Das  Anthracene  und  seine  Derivate.  G.  Auerbach,  Braunschweig,  1880. 


MINERAL   OILS 

THE  PETROLEUM   INDUSTRY 

Petroleum  is  widely  distributed,  being  found  in  many  places  in 
sufficient  quantities  for  profitable  working.  The  principal  deposits 
in  America  are  located  in  Pennsylvania,  New  York,  Ohio,  West 
Virginia,  California,  Colorado,  and  Canada;  some  oil  comes  from 
Indiana,  Kansas,  Kentucky,  and  Texas.  The  next  in  importance  to 
the  American  oil  fields  are  the  Russian,  in  the  Baku  district  around 
the  Caspian  Sea,  in  the  Caucasus  mountains,  and  along  the  northeast 
coast  of  the  Black  Sea. 

Less  important  deposits  occur  in  Persia,  Burmah,  China,  Galicia, 
and  Romnania.  Small  deposits  are  worked  in  Germany,  Hungary, 
Algiers,  Japan,  Venezuela,  New  Zealand,  and  in  some  of  the  islands 
of  the  Pacific. 

Petroleum  occurs  in  all  geological  formations  from  the  Silurian 
to  the  Tertiary,  the  New  York  and  Pennsylvania  deposits  being  in 
the  Devonian  a,nd  Upper  Silurian,  the  Colorado  fields  in  the  Creta- 
ceous, and  those  in  California  in  the  Miocene  epoch  or  Middle  Ter- 
tiary. The  Russian,  Galician,  and  Indian  oils  are  chiefly  in  the 
Tertiary.  In  all  cases,  the  strata  in  which  it  is  found  are  horizontal 


286  OUTLINES   OF  INDUSTRIAL   CHEMISTRY 

or  but  slightly  inclined,  usually  not  over  30°.  It  is  generally  found 
in  sandstones  or  conglomerates,  called  "  oil  sands,"  overlaid  with  an 
impervious  shale  or  slate.  Frequently  several  layers  of  sandstone 
are  struck,  lying  between  beds  of  the  shale. 

The  origin  of  petroleum  has  been  the  subject  of  much  study  by 
many  eminent  chemists.  Berthelot  regarded  it  as  the  product  of 
the  action  of  steam  and  carbon  dioxide  on  the  alkali  metals.  Men- 
deleeff  supposed  it  resulted  from  the  decomposition  of  metallic  car- 
bides by  water.  This  necessitates  the  acceptance  of  La  Place's 
theory  of  the  formation  of  the  earth,  and  the  assumption  that  heavy 
metals,  such  as  iron,  were  among  the  first  substances  to  condense  into 
the  liquid  and  solid  state,  thus  forming  the  central  portion  of  the 
earth ;  and  that  these  metals  then  combined  with  the  carbon  from 
the  surrounding  atmosphere  to  form  carbides,  which  were  after- 
wards decomposed  by  water,  from  the  cooled  surface,  which  perco- 
lated down  through  cracks  and  fissures  caused  by  the  cooling  and 
shrinkage  of  the  earth's  crust.  Thus  hydrocarbons  were  formed  and 
metallic  oxides  left  in  the  earth.  This  theory  requires  that  all 
petroleums  have  approximately  the  same  composition,  in  whatever 
formation  they  are  found,  but  this  is  not  the  case. 

Another  hypothesis  supposes  petroleum  to  be  of  organic  origin. 
Here  again  are  several  theories  as  to  the  formation  of  the  oil  from 
the  vegetable  or  animal  remains.  One  is  that  the  organic  matter, 
probably  consisting  of  vegetable  matter  and  mollusks,  decomposed 
under  salt  water  with  exclusion  of  oxygen  and  at  a  rather  low  tem- 
perature.* Another,  that  only  animal  matter  is  the  basis  of  the  oil 
and  that  the  nitrogen  of  the  animal  tissues  escaped  as  ammonia  or 
other  nitrogen  compounds,  and  that  the  remaining  fat  was  subjected 
to  a  species  of  dry  distillation  under  great  pressure,  yielding  crude 
petroleum.  There  is  reason  to  believe  that  the  New  York,  Pennsyl- 
vania, and  Ohio  petroleums  are  of  vegetable  origin,f  but  those  of 
California,  $  Texas  and  some  others  contain  nitrogen  and  are  found 
in  rocks  filled  with  animal  remains. 

The  crude  oil  usually  consists  of  hydrocarbons,  present  in  homol- 
ogous series,  though  oils  from  different  localities  show  differences 
in  these  series.  The  Pennsylvania  oils  contain  members  of  the 
marsh  gas  series  with  the  general  formula,  CnH2n  +  2 ;  all  of  these, 
from  methane,  CH4,  up  to  solid  paraffines  with  C^H58,  have  been  iso- 

*  Phillips.    Am.  Chem.  Jour.,  16,  409-429. 

t  Orton.  Report  on  Occurrence  of  Petroleum,  Natural  Gas,  and  Asphalt  in  West- 
ern Kentucky.  1891. 

1  Peckham.    Am.  Jour.  Science,  48.     (1894.) 


MINERAL  OILS  287 

lated  from  these  oils.  Also,  small  amounts  of  the  olefine  series, 
CnH2n,  and  the  benzine  series,  CnH2n_<;,  and  in  some  oils,  some  sulphur 
and  nitrogen  have  been  found.  The  Russian  oils,  however,  consist 
largely  of  the  naphthene  series,  having  the  general  formula  CnH2n, 
isomeric  with  the  olefines,  but  differing  from  them  in  their  proper- 
ties. Consequently,  the  refining  of  the  Russian  oil  is  not  quite  the 
same  as  that  of  the  American  oils. 

In  many  places  crude  oil  comes  to  the  surface  in  small  quantities, 
mixed  with  the  water  from  springs,  the  first  discoveries  having  been 
reported  as  "oil  springs."  The  explorers  in  central  New  York,  as 
early  as  1630,  mentioned  an  Indian  remedy  containing  petroleum. 
Later  it  was  sold  as  "  Seneca  oil,"  by  the  Seneca  Indians.  Their 
method  of  collecting  it  was  to  spread  blankets  on  the  surface  of  the 
water  on  which  the  oil  was  floating,  wringing  it  out  when  the 
blanket  became  saturated.  If  the  layer  of  oil  was  thick  enough,  it 
was  skimmed  off  with  a  flat  board. 

About  the  middle  of  this  century,  petroleum  from  various  parts 
of  the  world  had  begun  to  attract  some  attention,  and  crude  methods 
of  refining  it  had  been  devised ;  in  some  few  instances  this  purified 
oil  was  being  used  for  illuminating.  But  none  of  these  efforts  had 
been  very  successful,  and  it  was  not  until  1859,  when  Mr.  Drake 
drilled  the  first  productive  oil  well  near  Titusville,  Pa.,  that  the  real 
development  of  the  petroleum  industry  began.5*  The  Russian, 
Indian,  and  Galician  oils  were  mentioned  by  explorers  during  and 
before  the  Middle  Ages,  but  the  industries  have  never  been  de- 
veloped to  any  great  extent,  until  within  the  last  twenty  years,  when 
the  Russian  fields  have  become  very  important. 

The  crude  oil  is  obtained  by  boring  tube  wells  through  the  shale 
into  the  sand  rock.  There  is  no  certainty  beforehand  that  a  well 
will  yield  oil,  and,  indeed,  about  one-fifth  of  those  bored  in  this 
country  produced  none;  these  are  called  "dry  holes." 

The  machinery  used  in  oil-well  drilling  is  very  ingen- 
ious, and  a  great  number  of  special  devices  have  been 
invented  to  overcome  the  numerous  obstacles  encountered. 
Only  the  principal  tools  can  be  mentioned  here.  The 
chief  one  is  the  "centre-bit"  (Fig.  72),  a  chisel-shaped 
piece  of  steel  4  feet  long  and  weighing  about  300  Ibs., 
the  cutting  edge  of  which  is  nearly  as  wide  as  the 
diameter  of  the  well.  Above  the  centre-bit  is  the 


*  A  period  of  wild  excitement  and  speculation  followed,  the  description  of  which 
by  Peckham,  Crew,  and  others,  is  very  interesting  reading. 


288  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

"  auger-stem,"  a  rigid  bar  from  12  to  45  feet  long,  to  which  the  bit 
is  screwed.  Its  chief  purpose  is  to  guide  the  bit  and  keep  the  hole 
straight;  it  also  adds  weight  to  the  drill.  Next  above  the  auger- 
stem  is  a  peculiar  piece  of  apparatus  called  the  "jars"  (Fig.  73). 
It  consists  of  two  links  of  steel  which  have  a  sliding  motion,  one 
within  the  other,  of  from  20  to  24  inches.  The  object  of  this  is  as 
follows  :  the  centre-bit  frequently  becomes  fastened  in  the  hole,  either 
by  fragments  of  broken  rock  acting  as  wedges  between  it  and  the 
sides  of  the  well,  or  through  sinking  into  a  seam  in  the 
rock.  Any  attempt  to  loosen  it  by  a  steady  upward  pull 
would  break  the  rope,  but  a  sudden  upward  shock  is  generally 
sufficient  to  loosen  it.  This  is  obtained  by  the  movable  links 
of  the  jars.  But  they  are  not  allowed  to  close  completely, 
and  so  give  a  downward  stroke,  unless  the  tools  become  fast 
in  the  well.  Above  the  jars  is  a  long,  heavy  steel  bar  called 
the  "  sinker-bar."  Through  its  momentum  this  gives  greater 
effect  to  the  action  of  the  jars.  To  the  top  of  the  sinker-bar 
the  rope  is  attached,  by  which  the  entire  mass  is  lifted  and 
dropped,  just  as  a  pile-driver  is  operated.  The  drop  allowed 
for  each  stroke  of  the  bit  is  about  two  feet.  The  rope  is 
fastened  to  the  "temper-screw,"  which  lowers  the  tools 
slightly  as  the  rock  is  cut  away  by  each  blow  of  the  bit, 
and  turns  them  in  the  hole  so  that  the  next  cut  shall  be 
at  a  slight  angle  to  the  last  one.  When  all  screwed  together, 
the  drilling  tools  form  a  rod  about  60  feet  long  and  weighing 
about  a  ton. 

Over  the  spot  where  the  well  is  to  be  drilled  a  heavy  timber 
structure  is  built,  called  the  "  derrick " ;  this  is  from  35  to  80  feet 
high,  and  from  12  to  15  feet  square  at  the  bottom,  tapering  to  about 
5  feet  square  at  the  top.  On  the  floor  of  the  derrick  is  the  windlass 
for  handling  the  drilling  tools,  the  rope  passing  over  a  small  wheel 
at  the  top.  During  the  drilling  the  rope  passes  through  a  clutch 
at  the  end  of  a  large  walking-beam,  driven  by  the  engine,  imparting 
a  rapid  up  and  down  motion  to  the  tools. 

An  iron  "drive-pipe"  is  sunk  through  the  drift  and  clay  to  the 
solid  bed-rock.  If  the  latter  is  within  15  or  20  feet  of  the  surface,  a 
shaft  6  or  8  feet  square  is  sometimes  dug  down  to  it.  Then  the 
drilling  of  the  well  proper  begins,  which  is  usually  7-J  inches  in 
diameter  to  the  bottom  of  the  water-bearing  strata.  Then  the  hole 
is  decreased  to  5|  inches  diameter,  and  a  tube,  called  the  "casing," 
is  put  down ;  this  is  provided  with  a  rubber  or  leather  collar  to  fit 
•closely  against  the  shoulder  formed  where  the  diameter  of  the  well 


MINERAL  OILS  289 

decreases,  making  a  water-tight  joint.     Then  the  hole  is  continued 
to  the  oil-bearing  strata,  by  means  of  a  5J-inch  bit. 

At  frequent  intervals  it  is  necessary  to  remove  the  mud  and 
splinters  of  rock.  This  is  done  by  the  "sand-pump,"  or  "bailer," 
which  is  a  long  metal  tube,  having  a  valve  in  the  bottom.  It  is  low- 
ered until  a  pin  on  the  under  side  of  the  valve  strikes  the  bottom  of 
the  well.  The  water,  which  is  always  present,  rushes  into  the  bailer, 
drawing  with  it  the  debris ;  then  the  tool  is  at  once  raised  and  the 
valve  closes. 

It  is  customary  to  drill  some  distance  into  the  oil-bearing  stratum, 
and  sometimes  a  cavity  filled  with  gas,  oil,  and  water  is  struck.  The 
pressure  is  occasionally  so  great  as  to  drive  the  oil  to  the  surface, 
sometimes  with  great  force.  Such  wells  are  called  "  gushers."  They 
seldom  continue  to  flow  for  more  than  a  few  days  or  weeks,  when 
pumping  must  be  employed.  Some  of  these  gushers  have  produced 
enormous  quantities  of  oil,  as  much  as  3000  barrels  a  day  when  at 
their  height. 

But  most  wells  do  not  gush,  and  it  is  now  quite  customary  to  re- 
sort to  "torpedoing,"  in  order  to  increase  the  yield  of  oil.  A  tin 
shell,  from  3  to  5  inches  in  diameter  and  from  5  to  20  feet  long,  is 
filled  with  nitroglycerine  and  lowered  to  the  bottom  of  the  well. 
On  top  of  the  can  is  a  percussion  cap,  which  is  fired  by  dropping  a 
piece  of  iron,  called  a  "go-devil,"  weighing  several  pounds,  into  the 
well.  The  resulting  explosion  cracks  and  shivers  the  rock,  giving 
the  oil  a  better  opportunity  to  flow  into  the  well.  Very  often  a  well 
gushes  after  torpedoing,  and  measures  are  usually 
taken  beforehand  to  dispose  of  the  first  heavy  rush  of 
oil  and  water. 

The  finished  well  is  prepared  for  pumping  by 
lowering  a  2-inch  pipe,  at  the  bottom  of  which  is 
the  oil  pump,  worked  by  a  wooden  rod  inside  the  pipe. 
Fig.  74  shows  sections  through  a  pumping  and  through 
a  flowing  well.  In  a  flowing  well  no  pump  rod  is 
introduced,  but  the  space  between  the  casing  and 
tubing  is  tightly  closed  at  the  top,  in  order  to  force 
both  gas  and  oil  through  the  tubing. 

The  wells  range  in  depth  from  50  to  4000  feet, 
the  average  in  ]N~ew  York   and   Pennsylvania  being 
from  1200  to  1800  feet.     The  cost  varies,  but  from 
3000  to  4000  dollars  is  about  the  average.     The  ordinary  produc- 
tion varies  from  one  to  several  hundred  barrels  per  day. 

The  crude  oil  is  now  generally  carried  from  the  wells  to  the 


290 


OUTLINES  OF   INDUSTRIAL   CHEMISTRY 


refineries  by  pipe-lines,  —  six-  or  eight-inch  pipe,  through  which  the 
oil  is  pumped.  At  frequent  intervals  along  the  pipe-lines  are  tanks 
of  from  30,000  to  40,000  barrels  capacity,  in  which  the  oil  is  stored 
until  wanted  for  refining.  Of  course  this  system  mixes  all  varieties 
of  oils ;  hence,  if  a  special  kind  is  required,  it  must  be  transported 
in  tank  cars  or  in  barrels. 

Crude  petroleum  is  a  thick,  sirupy  liquid  varying  in  color  from 
greenish  brown  to  nearly  black;  some  varieties  are  reddish  brown 
or  orange  when  viewed  by  transmitted  light.  Nearly  all  show  some 
fluorescence,  and  have  a  rather  unpleasant  odor.  The  specific  gravity 
varies  from  0.782  to  above  0.850,  in  oils  from  different  localities.  As 
it  comes  from  the  well,  more  or  less  gas  is  dissolved  in  it,  consisting 
chiefly  of  marsh  gas,  CH4 ;  ethane,  C2H6 ;  propane,  C3H8 ;  and  butane, 
C4H10.  A  very  small  amount  of  phosphorus  is  often  present,  but 
seldom  more  than  0.05  per  cent.  The  oils  from  Ohio  and  Canada 
have  a  very  unpleasant  odor,  because  they  contain  some  sulphur 
compounds.  Sand  and  water  are  also  mixed  with  the  crude  oil,  but 
these  settle  on  standing  in  the  storage  tanks. 

In  order  to  separate  the  various  products  from  the  crude  oil,  it  is 
subjected  to  fractional  distillation.  The  higher  the  percentage  of 
the  illuminating  oils,  the  more  profitable  for  the  refiner ;  but  many 
crude  oils  are  distilled  only  for  the  lubricating  oils.  A  few  may  be 
used  as  lubricants  without  distilling.  Considerable  petroleum  was 
used  for  fuel,  but  this  is  being  replaced  by  the  residuum  from  which 
the  more  valuable  illuminating  oils  have  been  separated. 

Refining  consists  in  the  separation  and  purification  of  the  market- 
able products  of  the  crude  oil,  which  is  usually  separated  into 


FIG.  75. 


about  five  portions.  These  are  naphthas,  illuminating  oils,  lubri- 
cating oils,  parafnnes,  and  coke.  The  process  is  usually  worked  in 
two  stages :  the  distillation  and  refining  first  of  the  light  oils,  and 
then  of  the  heavy  oils.  It  is  only  in  the  large  refineries  that  both 
processes  are  carried  out ;  usually  one  refiner  produces  the  naphthas, 


MINERAL   OILS 


291 


burning  oils,  and  "residuum,"  and  another  starts  with  the  residuum 
and  finishes  the  process. 

For  distilling  the  light  oils,  two  forms  of  still  are  in  use.  The 
cylindrical  or  horizontal  still  (Fig.  75)  is  about  30  feet  long  by  10  or 
12  feet  in  diameter,  and  is  set  in  a  brick  furnace,  with  the  upper 
half  of  the  still  exposed  to  the  air.  It  holds  about  600  barrels,  and 
is  provided  with  steam  coils  and  arrangements  for  blowing  in  free 
steam  during  the  distillation,  which  assists  in  the  process  by  mechan- 


FIG.  76. 


ically  helping  to  carry  over  the  oil  vapors.  The  upright  or  "cheese- 
box  "  still  (Fig.  76)  holds  1000  barrels  or  more,  is  set  directly  over 
the  furnaces  (B,  B),  and  is  exposed  to  the  air.  It  is  30  feet  in  diam- 
eter and  about  10  feet  high,  and  has  steam  coils  and  pipes  for  free 
steam  as  above  described.  The  bottom  is  double-curved  to  permit  of 
some  expansion. 

The  condensers  are  long  straight  pipes  set  in  troughs  through 
which  water  flows,  or  they  are  coils  set  in  tanks  of  cold  water. 
They  are  so  arranged  that  the  distillates  are  delivered  at  some  dis- 
tance from  the  still,  to  diminish  the  fire  risk.  Each  pipe  is  usually 
provided  with  a  trap  by  which  the  gases  (passing  over  with  the  oil 
vapors)  are  collected  and  then  led  under  the  still -and  burned,  thus 
economizing  fuel.  Sometimes  the  very  light  oils  are  burned  with 
the  gases,  but  they  are  usually  condensed,  forming  the  "benzine 
distillate,"  or  crude  naphtha.  This  is  stopped  when  the  gravity 
reaches  62°  Be.  (sp.  gr.  0.729).  Then  comes  the  kerosene,  or  burning 
oil  distillate,  until  the  gravity  equals  0.790,  or  for  very  heavy  illu- 
minating oils,  0.820.  Here  the  distillation  is  stopped  and  the  resid- 
uum drawn  off,  to  be  distilled  for  lubricating  oils,  in  the  "  tar 
stills." 

Since  the   illuminating  oils  are  the   most   valuable,  a  process 


292  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

known  as  "cracking,"  *  by  which  the  yield  of  these  is  increased,  has 
come  into  general  use  in  recent  years.  As  has  already  been  shown, 
the  upper  part  of  the  still  is  exposed  to  the  air  and  thus  cooled. 
When  the  heavy  oils  begin  to  distill,  the  fire  is  so  modified  that  only 
the  bottom  of  the  still  is  heated  very  hot,  while  the  top  and  sides 
cool  somewhat.  Thus  the  heavy-oil  vapors  are  condensed  within 
the  still  itself,  and  drop  back  into  the  residuum,  which,  being  much 
hotter  than  the  boiling  point  of  the  oil,  causes  a  breaking  up  of  the 
oils  of  high  molecular  weight  into  lighter  oils  of  less  molecular 
weight  and  lower  boiling  points,  while  some  carbon  separates,  form- 
ing a  coke  on  the  bottom  of  the  still.  This  deposit  of  carbon  must  be 
removed  at  frequent  intervals. 

The  reactions  which  occur  in  "cracking"  are  probably  complex. 
The  heavy  oils  are  decomposed  into  parafiines  and  olefines  of  lower 
boiling  points,  and  very  probably  hydrocarbons  of  the  aromatic  and 
methylene  series  are  also  produced.  The  number  of  products  is 
doubtless  quite  large.  As  examples  of  what  may,  perhaps,  take  place, 
the  following  may  be  assumed :  the  hydrocarbon,  C^Hgg  (octadecane), 
boiling  at  317°  C.,  might  decompose  into  C10H22  (decane),  boiling  at 
173°,  and  C7H16  (heptane),  boiling  at  98°  C.,  and  carbon.  Or  it  might 
form  a  paraffine  and  an  olefine,  e.g.  C8H18  (octane),  boiling  at  125°  C., 
and  C10H20  (decylene),  boiling  at  172°  C.  The  lower  boiling  product 
would  be  put  with  the  naphtha  distillate,  and  the  higher  boiling 
would  form  a  part  of  the  burning  oil. 

The  several  distillates  obtained  from  the  crude  oil  are  redistilled 
and  divided  into  further  subdivisions. 

The  benzine  distillate  yields  t  '•  — 

Cymogene,   B.  P.  =    32°  F.       Sp.  Gr.  =  0.590  -  0.610  ] 

Rhigolene,  B.  P.  =    60°  F.       Sp.  Gr.  =  0.625  -  0.631  \ 

Gasoline,     B.  P.  =  115°  F.       Sp.  Gr.  =  0.635  -  0.666  j 

C  Naphtha  (Benzine)  B.  P.  =  122°  -  140°  F.     Sp.  Gr.  =  0.678  -  0.700 

B  Naphtha,  Sp.  Gr.  =  0.714  -  0.718 

A  Naphtha  (Petroleum  naphtha),  Sp.  Gr.  =  0.741-0.745 

The  burning  oil  distillate  yields  :  — 

110°  fire  test  burning  oil  ("  Standard  white  ").  )  F  _, 

120°  fire  test  burning  oil  ("  Prime  white").         ( 
150°  fire  test  burning  oil  ("  Water  white"). 

*  The  history  of  the  discovery  of  this  process  is  given  in  chap,  iii  of  Petroleum 
Distillation,  by  A.  N.  Leet,  New  York,  1884. 

fBoverton  Redwood  —  Groves  and  Thorp's  Chemical  Technology,  Vol.  II. 


MINERAL   OILS  293 

The  residuum  from  the  above  distillation  is  transferred  to  the 
tar  still,  or  if  the  distillation  has  been  carried  on  under  vacuum,  it  is 
known  as  "reduced  oil,"  and  is  used  to  make  fine  lubricating  oils  or 
vaseline. 

The  tar  stills  are  cylindrical,  and  are  set  in  much  the  same  way 
as  those  already  described,  but  are  encased  in  brickwork  almost  to 
the  top.  They  are  provided  with  pipes  for  introducing  superheated 
steam,  and  are  much  smaller  than  the  crude  oil  stills. 

The  first  distillate  is  collected  until  the  gravity  is  about  38°  Be. 
(0.  834  sp.  gr.),  and  is  mixed  with  the  next  charge  of  crude  oil,  or 
washed  with  acid  and  soda  and  refined  for  burning  oil.  Then  follow 
several  distillates  of  increasing  color  and  density,  which  are  purified 
as  described  below,  and  treated  to  separate  the  paraffine  wax  and 
lubricating  oils.  The  distillation  is  carried  on  until  the  still  bottom 
is  red-hot,  when  a  gummy  yellow  distillate,  called  "yellow  wax,"  is 
collected.  This  contains  anthracene  and  other  hydrocarbons  of  high 
molecular  weight.  The  residue  of  coke  is  highly  valued  for  electric 
light  carbons  and  other  electrical  purposes. 

The  fractions  collected  from  the  burning  oil  distillate  are  more  or 
less  yellow,  colored  by  tarry  matters,  which  would  collect  in  the 
lamp-wick  and  soon  choke  it.  To  remove  these  impurities,  the  oil  is 
put  into  an  "  agitator,"  a  large,  lead-lined,  iron  tank,  where  it  is 
mixed  with  from  1  to  2  per  cent  of  concentrated  sulphuric  acid,  and 
the  mixture  stirred  by  blowing  in  air  at  the  bottom.  The  acid  unites 
with  the  tarry  matters,  and  when  the  blast  is  stopped,  sinks  to  the 
bottom  and  is  drawn  off  as  "sludge  acid."  Water  is  added,  and 
after  the  mixture  is  agitated,  is  drawn  off.  Next  a  solution  of  caus- 
tic soda  is  introduced  (about  1  per  cent),  and  the  contents  of  the  tank 
again  agitated.  Then  the  oil  is  again  washed  with  water  and  drawn 
into  the  settling  tanks,  where  the  suspended  water  settles  out,  leaving 
a  bright,  clear  oil.  These  tanks  are  very  shallow,  usually  only  about 
1  foot  or  15  inches  deep,  but  may  cover  an  area  of  20  by  30  feet. 
They  are  exposed  to  the  light  and  air,  and  usually  contain  steam 
coils  for  warming  the  oil  in  winter. 

If  the  oil  is  now  found  to  have  too  low  a  flash  point  (p.  295), 
it  is  run  through  a  "sprayer,"  an  upright  pipe  with  cross-arms  of 
small  perforated  pipe,  through  which  the  oil  is  forced  into  the  air  in 
fine  jets  or  spray;  after  falling  some  distance,  it  is  collected  in  tanks. 
By  this  exposure  to  air,  any  light  oils,  such  as  benzine  or  naphtha, 
are  volatilized,  and  the  flash  point  thus  raised.  But  spraying  is  less 
frequently  necessary  now,  since  more  care  is  taken  in  the  original 
distilling. 


294  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

Instead  of  washing,  some  kerosenes  are  redistilled,  but  this 
generally  fails  to  remove  all  the  yellow  color,  though,  when  burned, 
they  do  not  form  a  crust  on  the  wick,  due  to  traces  of  caustic  soda 
or  sodium  sulphate. 

A  small  amount  of  burning  oil  of  very  high  fire  test  (about 
300°  F.)  is  made  by  treating  a  crude  oil  distillate  (0.823  to  0.846 
sp.  gr.)  with  a  very  large  proportion  (5  to  7  per  cent)  of  sulphuric 
acid,  washing  with  caustic  soda,  and  redistilling  with  caustic  soda 
lye  in  the  still.  This  oil  is  sold  as  mineral  colza,  mineral  seal,  and 
mineral  sperm  oil. 

The  paraffine  oils  are  treated  with  acid  in  agitators  which  may  be 
heated  by  steam  pipes ;  they  are  washed  and  then  chilled  and  left 
several  hours  until  the  paraffine  crystallizes.  The  soft  mass  is  then 
put  into  canvas  bags  and  pressed  at  40°  F.  in  hydraulic  presses. 
The  crude  paraffine  cake  is  again  melted,  crystallized,  and  pressed. 
It  is  then  washed  with  a  little  benzine  and  pressed  once  more.  It 
is  finally  melted  and  filtered  hot  through  bone-char,  and  on  cooling, 
forms  the  white  commercial  paraffine.  The  oils  expressed  are  lubri- 
cating oils  of  various  grades. 

After  the  paraffine  is  removed,  some  of  the  lighter  lubricating 
oils  are  converted  into  "neutral  oils"  by  bone-char  filtration  and 
exposure  to  sunlight  and  air,  to  remove  the  "  bloom,"  so  that  they 
may  be  used  to  adulterate  certain  animal  and  vegetable  oils.  It 
may  also  be  removed  chemically  by  adding  about  1  per  cent  of  nitro- 
naphthalene,  or  dinitrobenzol,  or  nitric  acid.  Bloom  has  no  injurious 
effect  upon  the  oil  or  machinery. 

Crude  petroleums  containing  sulphur  (e.g.  those  from  Ohio  and' 
Canada)  are  more  difficult  to  refine,  and  consequently  were  formerly 
only  used  for  fuel.  Successful  methods  for  refining  them  are,  how- 
ever, now  in  use.  The  common  process  is  to  pass  the  vapors  from 
the  crude  oil  distillation  over  copper  oxide ;  or  to  collect  the  distil- 
lates from  the  crude  oil  separately  and  redistill  them  with  a  large 
excess  of  copper  oxide,  or  a  mixture  of  lead  and  copper  oxides  in  a 
still,  which  is  provided  with  an  agitator.  The  residue  consists  of  a 
mixture  of  tar,  copper  sulphide,  and  oxide.  This  is  pressed  and 
calcined  at  a  low  temperature,  the  combustion  of  sulphur  and  tar 
furnishing  sufficient  heat.  The  final  product  is  copper  oxide  which 
is  returned  to  the  process.  A  solution  of  litharge  in  caustic  soda  is 
sometimes  used  in  the  agitator  after  the  usual  acid  and  alkali  treats 
ment,  to  remove  the  sulphur,  but  this  is  not  always  a  success; 
though  it  destroys  the  offensive  odor,  traces  of  sulphur  sometimes 
remain  and  become  noticeable  on  burning. 


MINERAL  OILS  295 

The  lighter  lubricating  oils  are  called  "spindle  oils"  and  are 
used  on  rapid  running  bearings.  "  Machinery  oils  "  form  the  middle 
grades,  and  "  cylinder  oils  "  are  the  heaviest.  Paraffine  in  lubricat- 
ing oils  is  said  to  reduce  its  viscosity  and  cause  it  to  become  gummy 
when  in  use. 

"  Reduced  oils  "  are  made  from  the  residuum  left  after  distilling 
the  burning  oils  from  some  crude  petroleums  by  the  aid  of  vacuum 
(p.  5);  or  by  simply  exposing  certain  crude  oils  to  the  sun  and 
air  in  shallow  tanks  which  may  be  gently  heated  by  steam-coils  in 
winter.  The  very  light  oils  soon  evaporate  and  the  suspended  im- 
purities settle.  Another  process  is  to  let  the  crude  oil  flow  in  thin 
films  over  woollen  blankets  suspended  in  warm  rooms;  the  very 
volatile  oils  evaporate  and  much  of  the  suspended  matter  is  retained 
by  the  cloth.  By  these  methods,  oils  are  obtained  which  are  entirely 
free  from  any  decomposition  products  due  to  heating,  and  from  any 
chemicals  such  as  are  used  in  washing  and  bleaching  ordinary  lubri- 
cating oils.  Crude  oils  of  high  gravity  (below  32°  Be.)  are  usually 
selected  for  this  purpose. 

Reduced  oils  are  valuable  lubricators  and  command  a  good  price. 
Sometimes  they  are  char-filtered  to  improve  their  color  and  quality." 

Vaseline  or  petrolatum  is  made  from  the  residuum  of  vacuum  dis- 
tilled crude  oils.  It  is  treated  with  acid  and  soda,  washed  and  char- 
filtered,  and  sometimes  redistilled  in  vacuum. 

The  Russian  petroleums  are  distilled  in  much  the  same  way  aa 
the  American,  but  less  acid  is  used,  as  the  naphthenes  are  somewhat 
soluble  in  it.  It  is  found  practicable  to  use  continuous  stills  as  the 
residuum  is  more  fluid  than  in  the  case  of  American  oils.  The  stills 
are  heated  by  separate  furnaces  and  connected  in  such  a  manner  that 
the  overflow  pipe  from  one  is  the  supply  pipe  for  the  next,  the  resid- 
uum from  the  last  passing  through  coils  placed  in  the  supply  tank, 
so  that  the  crude  oil  is  warm  when  it  enters  the  first  still.  By  care- 
ful regulation  of  the  heat  and  the  flow  of  oil,  each  still  can  be  made 
to  yield  a  distillate  of  constant  gravity. 

Russian  petroleum  yields  about  38  per  cent  illuminating  oils, 
which  is  lower  than  the  Pennsylvania  oils.  Since  fuel  is  scarce,  the 
residuum,  called  astatki,  is  burned  in  special  burners  and  furnaces. 
The  yield  of  lubricating  oils  is  large,  being  nearly  36  per  cent. 
They  are  said  to  be  superior  to  American  lubricators  for  use  in  cold 
countries. 

Oil-testing.  —  The  usual  test  for  kerosene  is  the  flame  test,  i.e., 
the  determination  of  the  temperature  at  which  the  vapors  take  fire 
when  mixed  with  air.  The  point  usually  taken  is  the  "  flash  point," 


296 


OUTLINES   OF   INDUSTRIAL   CHEMISTRY 


the  temperature  at  which  the  oil  gives  off  sufficient  vapor  to  form  a 
momentary  flash  when  a  small  flame  is  brought  near  its  surface. 
The  "fire  test"  determines  the  temperature  at  which  the  oil  gives 
off  enough  vapor  to  maintain  a  continuous  flame  if  ignited;  in 
other  words,  it  shows  the  temperature  at  which  the 
oil  burns  in  the  air,  and  is  about  20°  F.  higher  than 
the  flash  point.  Both  the  flash  point  and  the 
burning  point  are  lower  than  the  boiling  point. 

The  flash  point  is  determined  in  a  special  appa- 
ratus, and  in  many  states  and  countries  the  par- 
ticular instrument  and  its  dimensions  are  specified 
by  law.  In  this  country,  "  open  testers  "  are  largely 
used,  but  recently  Abel's  "closed  tester"  has  be- 
come very  popular,  and  is  now  the  legal  instrument 
in  England  and  Germany.  There  are  many  forms 
of  apparatus  for  oil  testing,  but  the  two  above  men- 
tioned cover  the  general  principles  involved  in  all. 
Open  testers  do  not  represent  the  conditions  pre- 
vailing in  an  ordinary  lamp ;  the  closed  tester 
more  nearly  approaches  these,  and  its  indication 
is  usually  about  20°  F.  lower  than  that  shown  by 
the  open  tester. 

Tagliabue's  open  tester  (Fig.  77)  is  very  simple.  A  copper  water 
bath  (A),  heated  by  the  small  lamp  (B),  contains  the  glass  dish  in 
which  the  oil  to  be  tested  is  placed.  A  delicate 
thermometer  (E)  is  hung  to  dip  into  the  oil.  Some- 
times a  stirring  apparatus  is  provided  for  both  the 
water  bath  and  the  oil.  The  water  bath  is  slowly 
heated,  and  at  regular  intervals  of  temperature  a 
lighted  match  or  small  gas  flame  is  passed  half  an 
inch  above  the  surface  of  the  oil.  The  tempera- 
ture at  which  a  flame  passes  completely  over  the 
surface  is  noted  as  the  flash  point.  The  heating 
is  usually  continued  until  the  oil  catches  fire  on 
applying  the  light,  when  the  temperature  is  taken 
as  the  burning  point.  The  apparatus  is  rather 
crude  and  is  open  to  errors. 

Abel's  closed  tester  (Fig.  78)  is  more  compli- 
cated, but  obviates  some  of  the  errors  of  the  open 
cup.  It  consists  of  a  copper  cylinder  (K,  K)  in 
which  is  the  water  bath  (F).  In  the  upper  part 
of  the  water  bath  is  an  air  chamber  (B)  in  which 


FIG. 


Fiu.  76. 


MINERAL   OILS  297 

is  suspended  the  copper  vessel  (A)  carrying  the  oil.  All  these 
vessels  are  provided  with  close  fitting  covers.  The  cover  of  (A) 
has  three  openings  which  may  be  opened  or  closed  by  a  small 
lever.  The  cover  also  carries  the  thermometer  (D),  dipping  into 
the  oil,  and  a  small  lamp  or  gas  flame  set  on  an  axis  at  (C),  so 
that  the  flame  may  be  brought  directly  over  the  middle  opening 
in  the  cover.  Usually  the  lever  which  moves  the  cover  of  the 
opening,  simultaneously  turns  the  flame  down  to  it.  The  ther- 
mometer (E)  dips  into  the  water  bath,  which  is  heated  to  54°  G. 
before  the  oil  is  introduced  into  (A).  When  the  thermometer  (D) 
registers  18°-19°  C.  the  testing  is  begun,  and  repeated  with  each 
rise  of  a  degree,  until  the  flash  is  seen.  This  instrument  is  officially 
used  in  Germany,  the  lever  being  run  by  clock-work.  It  is  also  used 
in  England,  the  law  requiring  a  flash  test  of  73°  F.,  which  is  rather 
low  for  safety  ;  it  should  not  be  under  100°  F.  In  this  country,  each 
state  has  its  own  standard.  Some  require  150°  F.  fire  test  in  open 
cups,  and  others  110°  F.  Most  states  fix  110°  F.  flash  test. 

Lubricating  oils  are  usually  tested  for  viscosity,  gravity,  flash,  and 
burning  points,  congealing  point  and  color.  The  gravity  is  usually 
determined  with  the  hydrometer  or  Westphal  balance.  In  this 
country,  the  Baume  instrument  is  almost  always  used. 

Viscosity  is  determined  by  relative  tests,  e.g.,  the  rate  of  flow  of 
the  oil  through  a  capillary  tube  or  narrow  opening,  as  compared  with 
the  rate  of  flow  of  pure  sperm  oil  through  the  same  tube  or  opening. 
Temperature  is  here  a  very  important  factor. 

The  congealing  point,  or  "  cold  test,'7  determines  the  temperature 
at  which  the  oil  becomes  pasty  or  solid  through  the  crystallization 
of  dissolved  paraffine  or  other  matter.  This  test  is  of  great  moment 
if  the  lubricators  are  to  be  used  in  cold  climates. 

Color  tests  are  chiefly  made  on  oils  intended  for  export,  by  com- 
paring a  tube  full  of  the  oil  with  standard  glass  plates  of  various 
tints,  in  a  colorimeter.  For  burning  oils  the  colors  range  from  pale 
yellow  or  straw  to  water  white. 

Certain  animal  and  vegetable  oils,  when  soaked  up  in  waste,  will 
take  fire  on  standing.  This  is  especially  true  of  linseed,  cotton-seed, 
corn,  lard,  and  neatsfoot  oils,  and  is  caused  by  the  rise  in  temperature 
due  to  the  oxidation  of  the  oil.  If  from  40  to  50  per  cent  of  mineral 
oil  be  added  to  these  oils,  this  spontaneous  combustion  is  prevented 
to  a  great  extent.  This  is  one  of  the  uses  of  the  neutral  oils 
(p.  294). 


298  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

SHALE   OIL   INDUSTRY 

In  Scotland,  Germany,  and  a  few  other  countries,  mineral  oils 
are  produced  by  the  destructive  distillation  of  certain  bituminous 
shales.  These  are  soft,  light  brown,  or  gray  rocks,  which  do  not 
contain  oil  as  such,  but  are  permeated  with  bitumen,  a  very  complex 
organic  substance  similar  to  pitch.  When  heated  in  retorts  this 
decomposes  into  gas,  oily  products,  ammonia,  and  tar,  leaving  a 
carbonaceous  residue.  The  temperature  of  the  distillation  greatly 
influences  the  character  of  the  products,  a  low  temperature  affording 
an  increased  yield  of  oil. 

The  shale  is  broken  to  small  size  and  heated  to  a  low  red  heat  in 
vertical  retorts  into  which  steam  is  injected  to  assist  in  the  distilla- 
tion. Both  continuous  and  intermittent  systems  of  distillation  are 
in  use,  the  former  being  generally  employed  in  Scotland.  The  shale 
is  charged  at  the  top  of  the  retort  and  when  "spent"  is  drawn 
while  still  hot  upon  a  grate  beneath  the  retort,  where  its  carbona- 
ceous matter  (amounting  to  10-15  per  cent)  is  burned,  thus  econo- 
mizing fuel. 

The  products  of  the  distillation  pass  through  a  series  of  pipes 
similar  to  the  hydraulic  main  and  condensers  of  the  coal-gas  manu- 
facture. The  light  naphtha  vapors  and  gas  pass  into  a  coke  tower 
through  which  heavy  paraffine  oil  trickles ;  this  absorbs  the  naphtha, 
while  the  gas  passes  on  and  is  burned  under  the  retorts.  In  the 
hydraulic  main  and  condensers  the  other  distillates  condense  in  two 
layers,  the  ammoniacal  liquor  below  and  the  tar  and  oil  above. 
These  are  separated  by  gravity.  The  ammonia  liquor  is  treated  in 
the  same  way  as  that  from  coal  gas  (p.  125).  The  oily  tar  (0.865 
sp.  gr.)  is  distilled  in  much  the  same  way  as  crude  petroleum  until 
only  solid  coke  remains  in  the  still.  The  distillates  are  collected 
together  as  "  once  run  oil "  and  washed  in  agitators  with  sulphuric 
acid  and  caustic  soda,  and  then  fractionally  distilled.  These  dis- 
tillates are  each  purified,  yielding  commercial  naphtha,  burning 
oils,  lubricator  oils,  and  solid  paraffine. 

The  acid  tar  from  the  washing  yields  some  ammonium  sulphate, 
and  tarry  matter  which  is  used  for  fuel.  The  soda  tar  is  treated 
with  carbon  dioxide,  which  liberates  the  creosote,  used  for  the  same 
purpose  as  that  from  coal-tar.  The  carbonate  of  soda  solution  is 
causticized  and  used  again. 

OZOKERITE 

Ozokerite  is  a  natural,  paraffine-like  substance  containing  a  small 
quantity  of  oily  matter.  It  was  probably  formed  by  the  evaporation 


MINERAL  OILS  299 

of  petroleum  until  the  more  volatile  oils  had  escaped.  It  occurs  in 
irregular  seams  and  masses  in  the  earth  in  Galicia,  in  the  Caucasus, 
and  in  Colorado.  In  Galicia  it  is  mined  by  sinking  shafts  and  drift- 
ing, following  the  seams.  The  wax  is  separated  from  the  earthy 
impurities  by  hand  picking  and  by  washing,  the  wax  being  lighter 
than  water  and  rising  to  the  surface.  The  residue  is  boiled  with 
water  to  melt  out  the  remaining  wax,  which  is  skimmed  from  the 
surface.  Extraction  with  benzene  is  also  employed. 

The  wax  is  sometimes  distilled,  by  which  light  oils,  illuminating 
oils,  heavy  oil,  and  paraffine  are  obtained.  Or  it  is  refined  by  treat- 
ing with  sulphuric  acid  and  caustic  soda,  followed  by  a  charcoal  or 
bone-black  filtration.  The  product,  called  ceresine,  melts  at  61°  to 
78°  C.*  and  is  similar  to  beeswax.  It  appears  to  belong  among  the 
olefmes,  having  the  general  formula  CnH2n.  Its  color  ranges  from 
pale  yellow  to  white,  according  to  the  degree  of  refining. 

It  is  used  as  candle  stock ;  for  preparing  insulating  compounds 
for  electrical  work ;  in  making  a  black  dressing  for  shoes  and  har- 
ness leather,  and  to  adulterate  beeswax. 

ASPHALT 

Asphalt  or  mineral  pitch  is  probably  an  oxidized  residue  from  the 
evaporation  of  petroleum.  This  name  is  usually  applied  only  to  the 
solid  bitumens,  the  semi-solid  or  liquid  bitumen  being  called  maltha, 
or  mineral  tar.  Asphalt  generally  contains  sulphur  and  nitrogenous 
bodies,  but  is  chiefly  composed  of  hydrocarbons.  The  crude  mate- 
rial consists  of  two  chief  ingredients,  that  soluble  in  petroleum 
spirit,  called  petrolene,  and  an  insoluble  black  substance  called 
asphaltene.  Asphalt  occurs  in  large  quantities  in  and  near  the 
"  pitch  lake  "  on  the  island  of  Trinidad ;  also  in  Cuba,  Venezuelar, 
California,  Utah,  Texas,  Canada,  and  in  many  European  countries. 
The  Utah  deposit  is  particularly  pure  (gilsonite)  and  is  much  used 
for  black  varnish  and  for  insulating  material.  It  is  also  much  used 
as  a  protective  paint  for  the  interior  of  chlorine  stills,  bleaching 
powder  chambers,  acid  tanks,  and  for  waterproofing  purposes.  Its 
chief  use  is  for  sidewalks  and  pavements,  for  which  it  is  mixed  with 
pulverized  limestone  or  with  the  natural  asphalt  rock.  The  latter 
falls  to  a  loose  granular  mass  when  heated  until  the  asphalt  softens, 
and  is  then  rolled  and  stamped  into  place  with  hot  irons.  A  certain 
proportion  of  purer  asphalt,  or  of  the  heavy  petroleum  oils,  is  oft°n 
added  to  the  mixture  to  render  it  more  plastic. 

*  Redwood. 


300  OUTLINES  OF   INDUSTRIAL  CHEMISTRY 

Crude  asphalt  contains  much  moisture  and  mineral  matter.  It  is 
refined  by  heating  until  melted,  whereby  the  moisture  is  expelled 
and  some  of  the  mineral  matter  separates  by  subsidence.  Two 
varieties  of  Trinidad  asphalt  are  in  commerce,  —  "  lake  pitch  "  and 
"land  pitch."  The  latter  is  harder,  and  has  the  higher  melting 
point.  Asphalt  is  soluble  in  carbon  disulphide,  acetone,  and  ben- 
zene, but  not  in  alcohol  nor  water.  When  heated  it  softens  at  from 
80°  to  100°  C. 

REFERENCES 

Petroleum  Distillation.     A.  N.  Leet,  New  York,  1884. 

Report  on  Petroleum  ;   IT.  S.  Census,  1880.     S.  F.  Peckham,  Washington,  1885. 

Das  Erdb'l  von  Baku.     C.  Engler,  Stuttgart,  1887.     (Enke.) 

A  Practical  Treatise  on  Petroleum.     Benj.  J.  Crew,  Philadelphia,  1887.     (Baird 

&Co.) 

Die  Deutsche  Erdole.     C.  Engler,  Stuttgart,  1888.     (Enke.) 
Le  Petrole.     Henry  Deutsch,  Paris. 

Das  Erdb'l  und  seine  Verarbeitung.    A.  Veith,  Braunschweig,  1892.     (Vieweg.) 
Petroleum;   Its  History,  Origin,  etc.     William  T.  Brannt,  Philadelphia,  1895. 

(Baird  &  Co.) 

Die  Fabrikation  der  Mineralble.   W.  Scheithauer,  Braunschweig,  1895.  (Vieweg.) 
Treatise  on  Petroleum,  2  vols.     Boverton  Redwood  and  G.  T.  Holloway,  London, 

1896.     (Griffin  &  Co.) 

U.  S.  Geological  Survey,  8th  report.     (Formation  of  Petroleum.) 
American  Chemical  Journal,  16,  406.     The  Origin  of  Petroleum  and  of  Natural 

Gas.     F.  C.  Phillips. 

Proceedings  of  the  American  Academy  of  Arts  and  Sciences,  Vol.  32.     Investi- 
gations on  American  Petroleum.    Charles  F.  Mabery. 
Proceedings  of  the  American  Philosophical  Society,  Vol.  36,  No.  154.     Origin 

and  Chemical  Composition  of  Petroleum.     S.  P.  Sadtler. 
Journal  of  the  Society  of  Chemical  Industry  :  — 

1890,  359.     The  Oil  Fields  of  India,  Burmah,  etc.    B.  Redwood. 
1894,  719,  Removal  of  Sulphur  from  Petroleum. 
1894,  790,  Origin  of  Petroleum.     F.  C.  Phillips. 
1894,  794,  Present  State  of  the  Petroleum  Industry. 
1894,  872,  American  and  Russian  Petroleums. 
Journal  of  the  Association  of  Engineering  Societies  :  — 

1894,  On  the  Composition  of  the  Ohio  and  Canadian  Sulphur  Pe- 
troleum.    C.  F.  Mabery. 

Mineral  Resources  of  the  United  States,  1882-1893. 

Report  of  Experts  on  Asphalt  Paving.     Department  of  Public  Works,  Philadel- 
phia, 1894. 

L'Asphalte.    Leon  Malo,  Paris,  1888.     (Baudry  et  Cie.) 

Mineral  Oils  and  their  By-Products.     I.  I.  Redwood,  London,  1897.     (E.  & 
F.  N.  Spon.) 


VEGETABLE   AND   ANIMAL  OILS 


301 


VEGETABLE   AND   ANIMAL  OILS,  FATS 
AND   WAXES 

These  oils  are  usually  called  "  fatty "  oils,  to  distinguish  them 
from  the  mineral  and  essential  oils.  They  are  very  widely  dissemi- 
nated in  nature,  both  in  plants  and  in  animals,  and  often  form  a 
large  percentage  of  the  weight  of  the  substance  in  which  they  are 
found.  They  differ  from  the  mineral  oils  in  their  chemical  composi- 
tion, being  compounds  of  organic  acids,  with  bodies  belonging  to  the 
group  called  alcohols;  i.e.  they  are  esters  or  compound  ethers  of  the 
organic  acids.  In  the  majority  of  cases,  the  alcohol  from  which 
these  esters  are  derived  is  glycerine,  or  glycerol,  C3H5(OH)3,  a  tri- 
atomic  alcohol;  but  occasionally,  e.g.  in  the  waxes,  a  mouatomic 
alcohol  is  the  base.  The  ethers  formed  from  glycerine  with  the 
fatty  acids  are  called  glycerides,  a  name  which  is  sometimes  applied 
to  the  oils  also.  The  glycerine  radical  C3H5  is  called  glyceryl. 

The  acids  most  commonly  found  in  these  glycerides  are  shown  in 
the  following  tables :  — 


SATURATED  ACIDS.  (ACETIC  SERIES.) 


ACID. 

FORMULA. 

MELTING 
POINT. 

BOILING  POINT. 

SPECIFIC 
GRAVITY. 

Butyric    .     . 

C4H802 

-    3° 

163°  C. 

0.958 

Caproic    .     . 

C6H1202 

-    1.5° 

205° 

0.929 

Caprylic  .     . 

C8H1602 

+  15° 

236° 

0.935 

Capric      .     . 

CioH2oO2 

+  30° 

269° 

0.930 

Laurie      .     . 

Ci2H24O2 

+  43.5° 

225°      at  100  mm.  pressure. 

Myristic  . 

Ci4H28O2 

+  54° 

250°      at  100  mm.  pressure. 

Palmitic   .     . 

CieH3202 

+  62° 

271.5°  at  100  mm.  pressure. 

Stearic      .     . 

Ci8H3eO2 

+  70.9° 

291°      at  100  mm.  pressure. 

- 

Arachidic 

C2oH4o02 

+  75° 

Carnabuic 

C24H4802 

+  72.5° 

Cerotic     .     . 

C2?H5402 

+  78° 

302  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

UNSATURATED   ACIDS.     (ACRYLIC    SERIES.) 


ACID. 

FORMULA. 

MELTING  POINT. 

BOILING  POINT. 

C3H402 

8°C 

140°  C 

Crotonic 

C4H6Oa 

72° 

180° 

Hypogaeic  /      .     .     .     . 
Physetoleic  f     .     .     .     . 
Oleic   . 

C16H3002 

ClsH<uOe> 

(33° 
(30° 
14° 

Emcic  / 

134° 

\.>22ni4t>\J% 

J 

/60° 

UNSATURATED    ACIDS.     (PROP10LIC   SERIES.) 


ACID. 

FORMULA. 

MELTING  POINT. 

SPECIFIC  GRAVITY. 

Linoleic 

Liquid  at       18°  C 

Linolenic  
Ricinoleic      .     .     .     . 

CisH3o02 

CisHs^Og 

-  10°  C. 

0.940 

The  acids  containing  ten  or  fewer  carbon  atoms  in  the  molecule 
may  be  distilled  under  ordinary  atmospheric  pressure  without  de- 
composition ;  they  are  called  volatile  fatty  acids.  The  others  given 
in  the  tables  are  called  non-volatile  acids;  some  of  them  may  be 
distilled  uiidecomposed  under  reduced  pressure  or  by  superheated 
steam. 

With  the  exception  of  a  few  of  the  less  common  oils  and  waxes, 
only  acids  having  an  even  number  of  carbon  atoms  in  the  molecule 
occur  in  the  fatty  oils.  The  glycerides  composing  the  greater  part 
of  the  important  commercial  fats  are  those  of  butyric,  lauric,  pal- 
mitic, stearic,  oleic,  linoleic  and  ricinoleic  acids ;  to  a  less  extent 
occur  the  esters  of  caproic,  caprylic,  crotonic,  and  myristic  acids. 
The  fats  are  always  mixtures  of  several  glycerides,  and  the  propor- 
tion in  which  these  are  present  determines  the  nature  of  the  fat, 
whether  hard,  soft,  or  liquid ;  while  certain  peculiar  properties  of 
some  fats  are  due  to  the  presence  of  one  or  two  particular  gly- 
cerides. 

The  glycerides  of  palmitic  and  stearic  acids  are  white  crystalline 
solids,  melting  at  61°  and  72°  C.  respectively ;  that  of  oleic  acid  is 
liquid  at  ordinary  temperature. 


VEGETABLE   AND   ANIMAL  OILS  303 

The  fatty  acids  are  monobasic,  and  glycerine  being  a  triatomic 
alcohol,  the  glycerides  are  composed  of  three  acid  radicals  combined 
with  one  alcohol  rest;  thus  the  glyceride  of  palmitic  acid  has  the 
formula  (C16H3102)3=C3H5,  and  is  called  tripalmitin,  or,  more  often, 
simply  palmitin.  The  glyceride  of  stearic  acid  is  (C  18H.K02)5=C3~KS, 
called  tristearin  or  stearin.  That  of  oleic  acid  is  (CigH^j^CjHa 
called  triolein  or  olein. 

The  fats  and  oils  are  lighter  than  water.  They  cannot  be  boiled 
or  distilled,  even  under  reduced  pressure,  for  when  heated  much 
above  their  melting  point  they  decompose.  Among  other  products 
of  decomposition  is  a  substance  called  acrolein,  CH2=CH— CHO. 
This  is  a  low  boiling  liquid,  having  a  very  disagreeable  odor,  and 
whose  vapors  are  very  irritating  to  the  eyes. 

Fresh  fats  are  nearly  odorless  and  of  neutral  reaction,  but  when 
exposed  to  the  air  for  some  time  many  of  them  undergo  a  change  by 
which  the  glycerides  are  decomposed  and  the  fatty  acids  set  free, 
while  glycerine  is  formed  and  usually  further  decomposed  at  once. 
This  breaking  up  of  an  organic  ester  into  free  acid  and  an  alcohol  is 
called  hydrolysis,  since  the  elements  of  water  are  taken  up  by  the 
acid  and  alcohol.  Thus  if  E.  represent  the  acid  radical,  hydrolysis 
of  a  fat  may  be  represented  by  the  general  equation :  — 

CH2OR  CH2OH. 

I  I 

CHOR  +  3  H-OH  =  CHOH  +  3  H-OR. 

I  i 

CH2OR  CH2OH. 

s 

This  change  is  often  brought  about  by  the  fermentation  or  putre- 
faction of  other  substances  of  a  gelatinous  or  albuminous  character 
present  in  the  oil,  and  is  accompanied  by  numerous  secondary  re- 
actions, which  produce  bodies  of  a  very  disagreeable  odor  and  taste. 
The  oil  is  then  said  to  be  "  rancid." 

Hydrolysis  may  be  readily  brought  about  by  chemical  means,  and 
is  then  called  "  saponification " ;  in  this  case  the  reaction  is  much 
more  complete,  and  these  secondary  reactions  do  not  occur.  The 
process  is  employed  in  soap  and  glycerine  manufacture,  as  will 
appear  later. 

Certain  oils  are  oxidized  when  exposed  to  the  air,  and  are  con- 
verted into  thick  gummy  or  resinous  masses,  or  in  thin  layers  form 
dry,  hard,  transparent  or  translucent  films.  This  change  is  called 
"  drying,"  and  is  most  noticeable  in  oils  containing  the  glycerides  of 


304 


OUTLINES  OF  INDUSTRIAL  CHEMISTRY 


linoleic,  linolenic,  and  ricinoleic  acids,  which,  being  unsaturated, 
oxidize  very  readily. 

Oils  and  fats  are  found  in  every  part  of  plants  and  animals, 
certain  parts  being  richer  than  others.  In  plants,  the  seeds  or  fruit 
generally  contain  the  most  oil,  but  the  quantity  varies,  even  in  the 
same  variety  of  plant,  according  to  the  soil,  cultivation,  climate,  and 
the  maturity  of  the  fruit.  Usually  it  is  in  inverse  ratio  to  the 
amount  of  sugar  and  starch  present.  In  animals,  most  of  the  fat 
is  found  in  the  abdominal  cavity,  surrounding  the  kidneys,  or  in  a 
layer  just  beneath  the  skin.  The  latter  is  especially  true  in  the  case 
of  marine  animals  (whales,  etc.)  and  those  living  in  cold  climates. 

The  vegetable  oils  are  obtained  by  crushing  or  grinding  that  part 
of  the  plant  richest  in  oil,  and  then  pressing  the  crushed  material, 

or  extracting  it  with  some  solvent, 
such  as  benzine  or  carbon  disul- 
phide.  Mills  for  crushing  olives 
are  of  great  antiquity,  the  oldest 
form  being  light  edge-runners  of 
wood  or  stone,  that  did  not  break 
the  kernels.  Heavy  edge-runners 
of  stone  or  iron  (Fig.  79)  are  used 
at  the  present  time,  but  steel  rolls 
and  buhr-stone  mills  are  more  gen- 
erally employed.  The  edge-runner 
consists  of  two  heavy  rollers  (A,  A), 
fixed  on  a  common  axle  (B),  and 
travelling  in  a  circle  around  a  verti- 
cal shaft  (C).  The  rollers  rest  on 
a  solid  stone  or  metal  bed  (D),  on 
which  the  material  to  be  ground  is 
spread.  Scrapers  (E)  are  fixed  on 
the  shaft  so  that  they  bring  the  material  directly  into  the  path  of 
the  rollers. 

The  ground  pulp  is  pressed  in  strong  canvas  or  horsehair  bags. 
Sometimes  part  of  the  oil  is  expressed  cold,  and  the  meal  is  then 
heated  and  pressed  a  second  time  while  hot.  Cold-pressed  oils  are 
lighter  color  and  of  better  quality,  but  hot  pressing  gives  a  larger 
yield.  Wedge-presses  and  screw-presses  were  used  in  ancient  times, 
but  the  invention  of  the  hydraulic  press  by  Bramah  in  1795  revo- 
lutionized oil  pressing.  Knuckle-joint  and  eccentric  presses  are 
later  inventions,  but  are  not  so  extensively  used. 

The  hydraulic  press  (Fig.  80)  consists  of  a  large  piston  or  ram 


FIG.  79. 


VEGETABLE    AND   ANIMAL   OILS 


305 


FIG.  80. 


(R),  which  is  forced  out  of  its  cylinder  (C)  by  the  hydrostatic  pros- 
sure  of  a  liquid  pumped  into  the  cylinder  in.  a  small  stream.  The 
bags  of  pulp  (B)  are  placed  between 
the  ram  and  a  fixed  top  plate  (P), 
and  the  oil  expressed  is  caught  in 
troughs  placed  around  the  ram  head. 

In  1850  Jesse  Fisher  of  Birming- 
ham, England,  invented  the  extrac- 
tion process,  using  a  volatile  solvent 
such  as  carbon  disulphide,  or  better, 
petroleum  naphtha.  The  solvent  is 
pumped  into  a  closed  vessel  contain- 
ing the  pulp.  After  extraction,  the 
solution  of  oil  in  the  solvent  is  drawn 
off  and  the  latter  recovered  by  dis- 
tilling it  off  from  the  oil.  This 
method  gives  a  larger  yield  of  oil, 
comparatively  free  from  gelatinous 
matter,  but  some  resins  and  coloring 
matter  may  be  dissolved,  thus  con- 
taminating it.  A  very  complicated  and  expensive  recovery  plant 
which  is  also  costly  to  operate  is  required.  Moreover,  if  the 
extraction  is  carried  too  far,  the  residue  of  crushed  seed  pulp  has 
no  value  as  animal  food  and  can  only  be  used  as  fertilizer  or  fuel. 
Pressing  involves  less  fire  risk  and  yields  a  lighter  colored  oil, 
especially  if  done  cold,  while  the  press-cake  from  many  vegetable 
oils  has  a  high  value  as  cattle  food,  owing  to  the  oil  remaining 
in  it. 

Animal  oils  are  contained  in  cells  composed  of  membraneous 
tissue  which  putrefies  soon  after  the  animal  is  killed,  causing  the 
fat  to  become  rancid  and  have  a  bad  odor.  Consequently  it  must  be 
rendered  immediately.  These  oils  are  obtained  by:  (a)  melting, 
"  trying  out "  or  rendering  in  open  kettles.  The  fat  is  chopped  into 
small  bits  and  heated  over  a  fire  with  a  very  little  water.  The 
tissue  shrivels  together  forming  "  cracklings,"  which  float  on  the  oil 
and  are  removed  by  straining  and  are  pressed  to  obtain  all  the  oil. 
Much  care  is  required  to  prevent  overheating,  and  this  process  has 
been  generally  abandoned  in  favor  of  steam  rendering  (see  below) ; 
(6)  by  boiling  with  water  to  which  sulphuric  acjd  is  sometimes 
added  to  decompose  the  cell  walls,  thus  liberating  the  oil ;  (c)  by 
heating  with  direct  steam  under  pressure  in  large  digesters  or  auto- 
claves (Fig.  81),  breaking  down  the  cell  walls.  The  fat  is  intro- 


306 


OUTLINES  OF   INDUSTRIAL   CHEMISTRY 


duced  through  the  manhole  (B)  which  is  closed  when  the  digester 
is  nearly  filled  to  the  top,  and  steam  at  about  50  pounds  pressure  is 

admitted  by  the  pipe  (C)  entering  near 
the  bottom.  Before  closing  the  di- 
gester, the  fat  is  sometimes  washed 
by  flushing  with  water  which  runs  off 
by  the  cocks  (D)  and  (E).  The  foul- 
smelling  gases  given  off  during  the 
rendering  are  conducted  away  by  the 
pipe  (H),  and  after  cooling  to  con- 
dense steam  they  are  discharged  into 
the  chimney  or  into  a  closed  sewer. 
After  several  hours  heating,  the  steam 
is  cut  off,  the  pressure  relieved,  and 
the  digester  allowed  to  remain  quiet 
until  the  oil  has  risen  to  the  top,  leav- 
ing the  cracklings  and  condensed  water 
in  the  bottom  of  the  tank.  The  prog- 
ress of  the  separation  may  be  followed 
by  trials  at  the  test-cocks  (F,  F).  The 
water  is  then  drawn  off  through  (E), 
until  the  oil  reaches  the  level  of  (G),  through  which  it  is  then 
drawn  off.  The  cracklings  are  discharged  by  dropping  the  lower 
manhole  cover  (J). 

In  testing  fatty  oils,  certain  distinguishing  properties  and  reac- 
tions are  sought.  The  specific  gravity  is  an  important  indication  as 
to  the  purity  of  the  sample.  It  is  determined  by  the  Westphal  bal- 
ance, Sprengel  tube,  or  specific  gravity  bottle. 

The  saponification  value  *  represents  the  number  of  milligrams  of 
potassium  hydroxide  needed  to  saponify  one  gram  of  the  oil.  It  is 

determined  by  saponifying  one  or  two  grams  of  the  oil  with  25  cubic 

T^ 
centimeters  of  —  alcoholic  potassium  hydroxide  and  titrating  the  ex- 

LI 

N 

cess  alkali  with  —  hydrochloric  acid,  using  phenolphthalein  as  indi- 
cator. 

The  iodine  (or  bromine)  value*  represents  the  percentage  of 
iodine  (or  bromine)  absorbed  by  the  oil,  forming  addition,  or  to  a 
smaller  extent,  substitution  products.  The  saturated,  fatty  acids 
and  their  glycerides  do  not  combine  with  the  halogens  to  any  appre- 


Fio.  81. 


*  Oils,  Fats,  and  Waxes.    Benedikt-Lewkowitsch. 


VEGETABLE   AND   ANIMAL   OILS  307 

uiable  extent ;  but  those  of  the  oleic  or  ricinoleic  series  combine  with 
two  atoms  of  iodine  (or  bromine) ;  those  of  the  linoleic  unite  with 
four,  and  of  the  linolenic  with  six,  atoms  of  the  halogen.  Thus  the 
determination  of  this  value  affords  a  method  of  determining  the  per- 
centage of  unsatarated  fatty  acids  (or  glycerides)  present  in  the  oil. 
The  weighed  amount  of  oil  (0.2  gram)  dissolved  in  chloroform  is 
mixed  with  a  standard  solution  of  iodine  in  mercuric  chloride  and 
shaken  gently.  After  standing  in  the  dark  for  four  hours,  the  ex- 

N 

cess  of  iodine  is  titrated  with  —  sodium  thiosulphate.*     The  number 

of  cubic  centimeters  of  thiosulphate  used,  multiplied  by  its  value 
in  terms  of  iodine,  gives  the  number  of  grams  of  iodine  absorbed 
by  the  oil ;  this  divided  by  the  weight  of  oil  used  and  multiplied  by 
100  gives  the  iodine  value. 

The  Maumene  test  f  shows  the  amount  of  heat  developed  when 
oil  is  mixed  with  sulphuric  acid.  Fifty  grams  of  the  oil  are  treated 
with  ten  cubic  centimeters  of  strong  acid  under  exact  conditions, 
and  the  "  rise  in  temperature  "  observed. 

The  elaidin  test  depends  upon  the  fact  that  nitrous  anhydride 
(N"208),  when  brought  into  contact  with  olein,  converts  it  into  the 
isomeric  solid  elaidin,  but  the  glycerides  oi  linoleic,  linolenic,  and 
isolinolenic  acids  are  not  affected  by  this  treatment.  Thus  the  non- 
drying  oils  become  solid,  while  the  semi-drying  and  drying  oils  re- 
main liquid,  or  at  most,  become  buttery.  Five  grams  of  oil  are 
mixed  with  seven  grams  of  nitric  acid  (1.34  sp.  gr.),  about  one  gram 
of  copper  wire  added,  and  the  glass  placed  in  cold  water  (15°  C.) 
and  the  oil  well  stirred.  After  standing  two  or  three  hours  the 
solidity  of  the  elaidin  cake  is  examined. 

For  convenience  in  study,  the  fatty  oils  are  generally  classified 
according  to  certain  similarities  in  their  properties  and  sources.  A 
convenient  classification  is  as  follows  $  :  — 

A.   Oils  and  Fats.    Glycerides. 

I.   OILS  OR  LIQUID  FATS. 
1.    Vegetable  Oils. 

1.  Drying  Oils. 

2.  Semi-Drying  Oils. 

3.  Non-Drying  Oils. 

*  Oil  Analysis.    A.  H.  Gill.  t  Corapt.-Rend.,  35  (1852),  572 

t  Oils,  Fats,  and  Waxes.    Benedikt-Lewkowitsch. 


308  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

2.   Animal  Oils. 

1.  Marine  Animal  Oils. 

(a.)  Fish  Oils. 
(6.)   Liver  Oils. 
(c.)    Blubber  Oils. 

2.  Terrestrial  Animal  Oils. 
II.    SOLID  FATS. 

1.  Vegetable  Fats. 

2.  Animal  Fats. 

B.  Waxes.    Non-Glycerides. 

I.   LIQUID  WAXES. 
II.   SOLID  WAXES. 

1.  Animal  Waxes. 

2.  Vegetable  Waxes. 


A.   OILS  AND  FATS 

VEGETABLE  DRYING   OILS 

Linseed  oil  is  derived  from  the  seeds  of  the  flax  plant  Linum 
usitatissimum,  L.,  which  is  extensively  cultivated  in  Northern 
Europe,  Italy,  Turkey  (near  the  Black  Sea),  India,  Argentina,  and 
in  the  United  States.  When  the  plants  are  raised  for  their  fibre 
(p.  435),  they  are  pulled  up  before  the  seeds  are  ripe ;  such  seed 
must  be  aged  several  months  before  pressing,  but  the  best  oil  is 
obtained  from  ripe  seed.  The  yield  is  from  25  to  32  per  cent,  ac- 
cording as  the  seeds  are  pressed  or  extracted.  The  cold-pressed 
cake  is  often  heated  and  pressed  again.  Cold-pressed  oil  is  a  clear, 
golden  yellow,  while  the  hot-pressed  product  is  amber  or  brown.  The 
latter  may  be  "bleached"  by  treating  with  a  solution  of  ferrous  or 
zinc  sulphate  and  exposing  it  to  the  sunlight.  The  crude  oil  is  puri- 
fied by  agitation  with  sulphuric  acid,  followed  by  washing  with 
water;  it  is  then  called  "raw  oil." 

Linseed  oil  is  the  most  important  of  the  drying  oils.  It  contains* 
about  65  per  cent  of  the  glycerides  of  isolinolenic  acid,  C18H3002,  and 
15  per  cent  each  of  the  glycerides  of  linoleic,  C18H3202,  and  lino- 
lenic,  C18H3002,  acids  and  5  per  cent  of  olein.  These  glycerides  absorb 
oxygen,  and  are  probably  converted  into  anhydrides,  which  are  quite 
insoluble.  This  causes  the  oil  to  become  thick  and  darker  colored, 
and,  when  in  thin  films,  to  form  a  dry,  hard  varnish.  This  drying 

*  K.  Hazura.    Zeit.  fur  Angew.  Chem.,  1888,  312. 


VEGETABLE   AND   ANIMAL   OILS  309 

.may  be  hastened  by  the  so-called  " boiling"  of  the  raw  oil.  The  lat- 
ter is  heated  with  certain  salts  (such  as  litharge,  lead  acetate,  or  the 
peroxide  or  borate  of  manganese),  called  "driers,"  which  probably  act 
as  carriers  of  the  oxygen.  A  part  of  the  glycerides  is  decomposed 
and  the  insoluble  gummy  anhydrides  are  formed,  while  some  acrolein 
is  set  free.  The  boiling  is  carried  on  in  open  kettles  heated  by 
direct  fire  or  by  high  pressure  steam,  and  is  sometimes  aided  by 
blowing  air  into  the  hot  oil.  When  the  latter  has  lost  from  8  to  10 
per  cent  of  its  weight,  the  process  is  stopped.  The  temperature  em- 
ployed varies  with  the  kind  of  drier  used,  being  highest  (250°  C.) 
with  litharge;  but  this  gives  a  dark-colored  product.  The  lower  the 
temperature  the  lighter  colored  the  product,  and  the  longer  the  oil 
must  be  heated.  By  heating  the  oil  for  several  days  with  borate  of  man- 
ganese at  60°  C.  to  125°  C.,  a  very  light-colored  boiled  oil  is  produced. 
All  boiled  oil  should  stand  several  months,  or  even  a  year,  before 
use,  in  order  that  the  impurities  may  settle.  Very  little  of  the  drier 
is  dissolved  by  the  oil,  and  the  clarified  boiled  oil  is  decanted  from 
the  residue.  It  dries  very  readily,  and  is  much  used  for  paint  mix- 
ing. If  the  boiling  is  continued  for  ten  or  twelve  hours,  at  a 
high  temperature,  the  oil  becomes  a  thick,  sticky,  viscid  mass,  used 
as  the  basis  of  printers'  ink. 

It  will  be  noted  that  this  boiling  is  really  a  decomposition,  or, 
perhaps,  a  polymerization  process. 

Several  grades  of  linseed  oil  are  in  the  market,  the  Calcutta  being 
considered  the  best  in  this  country,  while  the  Western  and  La  Plata 
oils  are  often  of  poorer  quality.  In  Europe  the  Baltic  oil|  is  held  in 
high  esteem,  while  the  Indian  oils  are  regarded  as  low  grade.  Lin- 
seed oil  is  frequently  adulterated  with  mineral  oil,  or  with  rosin, 
corn,  menhaden,  or  cotton-seed  oil. 

Eaw  linseed  oil  has  a  specific  gravity  of  0.930  to  0.939;  a  saponi- 
fication  value  of  189  to  195,  and  an  iodine  value  of  170  to  188. 
(Boiling  lowers  the  iodine  number.)  It  does  not  yield  solid  elaidin. 
It  is  used  as  a  soap  stock  for  soft  soap,  in  some  kinds  of  paint,  for 
varnish  making,  and  for  rubber  substitute.  Boiled  oil  is  used  for 
paint,  for  printing  inks,  for  oilcloth  making,  and  in  the  preparation 
of  linoleum.  For  this  last,  the  partially  boiled  oil  is  exposed  to  the 
air  at  a  moderate  temperature  (20°  to  22°  C.),  until  oxidized  to  a 
translucent  jelly.  It  is  then  thoroughly  incorporated  with  ground 
cork,  and  is  rolled  into  sheets  and  dried. 

Press-cake  from  raw  oil,  is  one  of  the  most  valuable  cattle  foods. 

t  Lewkowitsch,  Oils,  Fats,  and  Waxes.  Allen,  Commercial  Organic  Analysis, 
Vol.  IL 


310  OUTLINES   OF   INDUSTRIAL  CHEMISTRY 

By  the  oxidation  of  certain  oils,  as  in  "drying,"  considerable  heat 
is  generated,  and  if  they  are  exposed  in  thin  layers,  on  porous,  in- 
flammable material  (e.g.  when  absorbed  in  cotton  rags  or  waste), 
spontaneous  combustion  frequently  takes  place.  This  is  particularly 
liable  to  occur  with  linseed  oil;  it  may  be  prevented  by  the  addition 
of  mineral  oils. 

Hemp  oil  is  obtained  from  the  seeds  of  the  common  hemp,  Can- 
nabis  sativa,  L.  The  yield  is  about  30  per  cent.  It  is  a  greenish 
yellow  oil  of  0.925  to  0.930  sp.  gr.  Its  saponification  value  is  190  to 
191.1,  and  its  iodine  value  143  to  148.  It  is  a  poor  drying  oil,  but  is 
used  in  paint  and  as  an  adulterant  for  linseed  oil ;  also  as  stock  for 
soft  soap.  The  press-cake  contains  sharp  bits  of  the  shell,  which 
render  it  unfit  for  cattle  food. 

Poppy  oil  is  a  good  drying  oil,  obtained  from  the  seeds  of  the 
poppy,  Papaver  somniferum,  L.  The  yield  is  about  45  per  cent  of 
a  thin,  yeilow,  odorless  oil  of  0.924  to  0.927  sp.  gr. ;  its  saponification 
value  is  190.1  and  iodine  value,  134  to  137.  It  is  used  as  a  salad  oil 
and  to  adulterate  olive  oil;  but  mainly  in  the  preparation  of  fine  col- 
ors for  artists'  use. 

Sunflower  oil  is  a  colorless  or  pale  yellow,  palatable,  nearly  odor- 
less oil,  obtained  from  the  seeds  of  the  common  sunflower,  Heliantlms 
annuus,  L.  The  yield  is  about  30  per  cent,  and  the  press-cake  is  a 
valuable  cattle  food.  The  oil  contains  the  glycerides  of  oleic, 
palmitic,  arachidic,  and  linoleic  acids.  Its  specific  gravity  is  0.924 
to  0.926;  saponification  value,  193  to  194;  iodine  value,  120  to  133. 
It  is  used  as  a  soap  stock,  for  wool  oiling,  and  to  adulterate  olive  oil. 

VEGETABLE   SEMI-DRYING   OILS 

These  oils  have  an  intermediate  position  between  the  true  drying 
and  the  non-drying  oils,  some  of  them  showing  distinct  drying  proper- 
ties, while  others  do  not.  This  is  also  indicated  in  their  iodine  values. 

Corn  oil  or  maize  oil  is  derived  from  the  germ  of  the  common 
corn,  Zea  Mays,  L.  The  germ  is  removed  from  the  grain  (which  is 
used  for  making  starch  or  alcohol),  and  when  pressed,  yields  a 
yellow,  fluid  oil  of  0.920  to  0.925  sp.  gr.  Its  saponification  value 
is  188  to  193;  its  iodine  value  111  to  123;  Maumene  test,  56°  to 
60°  C.  It  is  used  in  making  soap  and  lubricants,  and  the  press-cake 
is  an  excellent  cattle  food. 

Cotton-seed  oil  is  derived  from  the  seeds  of  the  cotton  plant, 
Qossypium  herbaceum,  L.  After  the  husks  are  removed  in  cylinders 
containing  rotary  knives,  the  seeds  are  crushed  in  a  roller  mill. 


VEGETABLE   AND   ANIMAL  OILS  311 

The  meal  is  heated  in  iron  kettles  at  75°  to  90°  C.,  and  pressed  in 
horsehair  bags.  The  yield  is  about  18  per  cent.  If  the  seeds  are 
hulled,  the  press-cake  is  a  valuable  cattle  food ;  otherwise,  the  sharp 
husks  render  it  unfit  for  anything  but  fuel  or  fertilizer. 

The  crude  oil  is  reddish-brown  to  black  in  color,  and  must  be 
refined  for  most  purposes.  It  is  settled  until  a  slimy  precipitate 
has  deposited,  then  agitated  with  a  caustic  soda  solution  of  1.060 
to  1.090  sp.  gr.,  and  again  allowed  to  settle.  The  sediment,  called 
"  foots,"  is  used  for  soap  stock.  If  the  oil  is  clarified  with  fullers' 
earth  and  chilled  below  12°  C.,  the  palmitin  and  stearin  crystallize 
and  are  removed  by  cold  pressing.  This  solid  fat,  called  "  cotton- 
seed stearin,"  is  used  in  making  oleomargarine.  The  oil  expressed 
is  clear  and  light-colored,  and  is  extensively  used  as  a  salad  oil  and 
to  adulterate  olive  oil.  It  is  also  used  in  the  manufacture  of  "  com- 
pound lard,"  "  cottolene,"  etc.,  for  which  it  is  mixed  with  about  one 
and  one-half  times  its  weight  of  beef  stearin ;  and  in  btitterine  and 
oleomargarine,  to  soften  them  in  cold  weather. 

Refined  cotton-seed  oil  has  a  pale  straw  color  and  a  specific 
gravity  of  0.922  to  0.930.  Its  saponification  value  is  191  to  196; 
iodine  value,  101  to  116 ;  the  elaidin  test  gives  a  soft  buttery  mass ; 
Maumene  test,  70°  to  90°  C.  It  is  usually  free  from  acids  and  has 
a  pleasant  taste.  The  poorer  grades  are  used  for  soap  making.  It 
is  not  often  adulterated,  but  occasionally  linseed  oil  is  mixed  with  it. 

Sesame  or  Gingili  oil  is  obtained  from  the  seeds  of  an  East 
Indian  plant,  Sesamum  Indicum,  L.,  which  is  also  grown  largely 
in  Egypt  and  Asia  Minor.  The  crushed  seeds  are  first  pressed  cold 
and  then  hot.  The  yield  is  30  to  50  per  cent  of  thin,  yellow, 
odorless  oil  of  pleasant  taste,  which  does  not  become  rancid  on 
exposure.  It  consists  of  76  per  cent  olein,  the  remainder  being 
glycerides  of  palmitic,  stearic,  and  myristic  acids.  Its  specific 
gravity  is  0.921  to  0.924;  saponification  value,  190  to  194;  it  yields 
a  soft  elaidin ;  the  iodine  number  is  103  to  110 ;  and  the  Maumene 
test,  65°  to  68°  C.  The  best  quality  is  used  as  a  table  oil  or  to 
adulterate  olive  oil ;  the  common  grades  are  good  burning  oils  or 
soap  stock. 

Rape-seed  or  colza  oil  is  obtained  from  the  seeds  of  several 
varieties  of  Brassica  campestris,  L.  The  seeds  are  crushed  and 
heated  by  steam  before  pressing  j  this  coagulates  the  albumin  and 
improves  the  quality  of  the  oil.  The  yield  is  about  36  per  cent  of 
crude  oil  which  is  refined  by  agitation  with  one  per  cent  sulphuric 
acid  and  washing  with  alkali ;  this  removes  traces  of  sulphuric  acid 
and  the  free  fatty  acids  formed  by  its  action.  The  lighter  colored 


312  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

and  best  grades  are  generally  called  colza  oil,  rape  oil  being  applied 
to  the  commoner  grades.  Both  contain  the  glycerides  of  oleic, 
stearic,  and  erucic  or  brassic  acids.  The  specific  gravity  ranges  from 
0.913  to  0.916  at  15.5°  C. ;  the  iodine  value  is  97  to  106;  saponifi- 
cation  value,  171  to  178;  by  the  elaidin  test,  solidification  takes 
place  very  slowly,  frequently  requiring  50  to  60  hours,  and  the 
elaidin  is  very  soft;  Maumene  test,  50°  to  62°  C. 

The  purified  colza  oil  is  a  pale  yellow  and  is  odorless ;  it  is 
chiefly  used  as  a  condiment  and  as  a  burning  oil.  It  is  often  adul- 
terated with  hemp,  cotton-seed  or  fish  oils  or  with  rosin  oil.  Common 
rape  oil  is  used  as  a  lubricant,  and  being  very  viscid,  is  frequently 
employed  as  a  standard  for  measuring  viscosity.  When  exposed  to 
the  air,  it  becomes  thick  and  gummy,  but  does  not  really  "  dry." 

Castor  oil  is  obtained  from  the  seeds  of  Ricinus  communis,  L. 
They  are  cold  pressed  for  the  first  grade  of  medicinal  oil,  and  hot 
pressed  for  the  common  qualities,  about  40  per  cent  of  oil  being 
obtained.  It  is  very  viscid,  of  0.960  to  0.970  sp.  gr.,  and  contains 
the  glycerides  of  stearic  and  ricinoleic  acids.  Its  saponification 
value  is  178 ;  iodine  value,  85 ;  and  Maumene  test,  47°  C.  It  is  very 
apt  to  become  rancid,  and  is  soluble  in  alcohol  and  glacial  acetic  acid, 
and  insoluble  in  petroleum  spirit.  Its  purgative  action  is  probably 
due  to  an  alkaloid  present  in  it.  Large  quantities  are  used  in 
making  "  Turkey-red  oil,"  which  is  prepared  by  treating  the  castor 
oil  with  sulphuric  acid  at  less  than  40°  C.,  and  washing  with  a 
strong  brine  to  remove  the  excess  of  acid.  The  oil  is  decanted 
from  the  brine  and  carefully  neutralized  with  ammonia  or  soda,  by 
which  Turkey-red  oil,  the  alkali  salt  of  ricinoleo-sulphuric  acid 
C18H33(HS03)03,  is  formed.  Oil  thus  prepared  has  largely  replaced 
that  made  from  olive  oil  for  use  in  dyeing  cotton  with  alizarine.  Its 
exact  composition  is  as  yet  uncertain,  various  views  having  been 
advanced.* 

Castor  oil  is  also  used  for  making  transparent  soaps  and  common 
soap ;  its  viscosity  being  greater  than  that  of  any  other  oil  at  the  ordi- 
nary temperature,  it  is  largely  used  as  a  lubricant  for  heavy  machinery. 

By  blowing  air  through  hot  cotton-seed,  linseed,  lard,  or  rape  oil, 
it  is  partially  oxidized  and  converted  into  a  thick  viscous  oil  of  very 
high  gravity  (0.942  to  0.970).  Mixed  with  mineral  lubricating  oils, 
these  "  blown  oils "  are  used  as  substitutes  for  castor  oil  for  heavy 
machinery. 

*  J.  Soc.  Chem.  Ind.,  1883,  537.  Liechti  and  Suida.  J.  Soc.  Chem.  Ind.,  1884, 
412.  Mueller  and  Jacobs.  Dingler's  polytechnisches  Jour.,  254,  346.  Schmid. 
J.  Soc.  Dyers  and  Colorists,  1891,  69.  Scheurer-Kestner. 


VEGETABLE   AND   ANIMAL   OILS  313 

VEGETABLE   NON-DRYING   OILS 

These  usually  contain  a  high  percentage  of  olein,  absorb  little  or 
no  oxygen  and  do  not  dry  in  the  air,  yield  solid  elaidin,  and  have 
lower  iodine  values  than  the  drying  oils. 

Peanut  or  earthnut  oil  is  obtained  from  the  fruit  of  Arachis 
hypogcea,  L.  The  oil  is  a  light  greenish  yellow,  with  a  peculiar 
odor  and  taste,  but  when  refined  and  bleached  is  colorless  and 
without  taste.  It  contains  glycerides  of  arachidic  and  hypogseic 
acids,  besides  olein,  palmitin,  and  others.  Its  specific  gravity  is 
0.916  to  0.922 ;  saponification  value,  190  to  196 ;  and  iodine  value, 
85  to  105 ;  Maumene  test,  44°  to  67°  C.  It  is  employed  as  an  adul- 
terant for  olive  and  lard  oils,  as  a  salad  oil,  and  for  soap  making. 

Olive  oil  is  obtained  from  the  fruit  of  the  olive  tree,  Olea 
Europwa,  L.  Both  the  fruit  pulp  and  the  kernel  contain  oil,  but 
the  former  yields  the  better  quality.  The  fruit  is  crushed  in  mor- 
tars or  edge-runners  (care  being  taken  not  to  break  the  kernels)  and 
cold  pressed.  A  small  quantity  of  "virgin  oil"  is  thus  obtained, 
which  is  used  as  a  condiment.  The  residue  is  stirred  up  with  hot 
water  and  pressed  harder  than  before ;  then  it  is  ground  a  second 
time,  crushing  the  seeds,  stirred  up  with  hot  water,  and  pressed  as 
hard  as  possible.  The  final  press-cake  is  extracted  with  carbon 
disulphide,  or  is  put  into  pits  with  water  and  allowed  to  ferment 
for  some  weeks.  The  oil  rises  to  the  top  and  is  skimmed  off. 

The  several  grades  of  oil  obtained  are  purified  by  heating  to 
coagulate  the  albuminous  matter,  and  settling.  A  dark-colored, 
mucilaginous  substance,  called  "  foots,"  deposits,  and  is  used  for 
soap  stock.  The  lighter  colored  oils  are  used  for  the  table  and  the 
others  for  lubricators,  illuminants,  and  soap  stock.  Considerable  of 
the  grade  called  "  Gallipoli "  is  used  for  making  "  Turkey-red  oil " 
and  for  oiling  wool  after  scouring. 

Olive  oils  vary  in  color  from  pale  yellow  with  a  greenish  tinge 
(due  to  traces  of  chlorophyl)  to  greenish  or  brownish  yellow  in  the 
poorer  qualities.  First-grade  oils  are  odorless  and  palatable,  but 
the  lower  grades  are  strong  smelling  and  usually  have  a  disagree- 
able taste.  On  exposure  to  the  air  olive  oil  is  very  apt  to  become 
rancid.  The  specific  gravity  varies  from  0.914  to  0.918 ;  its  saponi- 
fication value  is  185  to  196 ;  iodine  value,  77  to  88 ;  the  elaidin  test 
shows  a  solid  mass  within  two  hours,  which  is  not  displaced  by 
inverting  the  vessel ;  Maumene  test,  41°  to  45°  C.  The  oil  contains 
about  72  per  cent  of  olein  and  linolein,  and  about  28  per  cent  mixed 
palmitin  and  stearin.  Being  very  expensive,  it  is  frequently  adul- 


314  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

terated  with  cotton-seed,  sesame,  or  rape-seed  oil,  while  poppy,  lard, 
and  peanut  oils  are  less  commonly  used. 

MARINE   ANIMAL   OILS 

These  oils  absorb  oxygen,  do  not  yield  solid  elaidin,  and  have 
high  iodine  values.  They  are  glycerides,  and  are  liquid  at  ordinary 
temperatures.  It  should  be  noted  that  the  varieties  of  sperm  oil 
do  not  belong  with  this  group,  since  they  are  liquid  waxes,  although 
obtained  from  blubber. 

FISH   OILS 

These  are  obtained  by  boiling  the  entire  body  of  the  fish. 

Menhaden  or  pogy  oil  is  derived  from  a  small  fish,  Alosa  Men- 
haden. It  is  of  a  brownish  color,  has  a  fishy  odor,  and  dries  in  the 
air.  Its  specific  gravity  is  0.927  to  0.933 ;  saponification  value,  189 
to  192 ;  iodine  value,  148  to  160 ;  Maumene  test,  123°  to  128°  C.  It 
is  extensively  used  in  currying  (p.  520),  to  adulterate  linseed  oil 
and  as  a  substitute  for  it,  and  for  adulterating  whale  oils,  etc.  It  is 
itself  often  adulterated  with  mineral  oils. 

LIVER   OILS 

These  oils  contain  cholesterol  and  other  biliary  ingredients 
which  are  unsaponifiable. 

Cod-liver  oil  is  obtained  from  the  liver  of  the  codfish,  Gadus 
morrhua.  The  livers  are  rendered  by  steam  heat,  and  the  oil,  sepa- 
rated, is  chilled  until  the  stearin  solidifies,  when  it  is  pressed  and 
the  clear  oil  collected.  Several  grades  are  made,  —  pale,  light 
brown,  and  dark  brown.  The  pale  oil  is  a  limpid  light  yellow, 
having  little  taste  or  smell,  and  is  used  in  medicine ;  its  chief 
value  in  this  is  probably  due  to  the  presence  of  traces  of  biliary 
compounds,  rendering  it  very  readily  digested  and  assimilated. 
The  darker,  less  pure  grades  are  used  for  leather  dressing.  Cod- 
liver  oil  contains  glycerides  of  oleic,  myristic,  palmitic,  and  stearic 
acids,  some  volatile  fatty  acids,  and  cholesterine ;  also  traces  of 
iodine  and  phosphorus.  The  specific  gravity  is  0.922  to  0.930  at 
15°  C. ;  the  saponification  value,  182  to  189 ;  iodine  value,  141  to 
159;  Maumene  test,  102°  to  113°  C.  It  is  frequently  adulterated 
with  shark-liver  oil,  seal  oil,  and  other  fish  oils. 

Shark-liver  oil  is  chiefly  obtained  from  the  livers  of  the  sunfish, 
Squalus  maximus.  Its  specific  gravity  is  0.911  to  0.928.  It  is  a 
clear  yellow  oil,  containing  a  large  amount  of  cholesterine,  and  is 
chiefly  used  for  adulterating  cod-liver  oil  and  in  dressing  leather. 


VEGETABLE   AND  ANIMAL   OILS  315 

BLUBBER   OILS 

Whale  oil  or  train  oil  is  obtained  from  the  blubber  of  the  Green- 
land or  "right"  whale,  Balcena  mysticetus,  and  other  animals  of  the 
whale  tribe.  By  boiling  the  blubber  in  water,  the  oil  rises  to  the 
surface  and  is  skimmed  off.  It  is  yellowish  brown  in  color  and 
has  a  strong  fishy  odor.  Its  composition  is  variable  and  but  little 
is  known  about  it;  glycerides  of  some  of  the  lower  members  of 
the  acetic  series  are  often  present.  The  glyceride  of  valeric  acid, 
C5H1002,  is  characteristic  of  some  whale  oils.  The  specific  gravity 
is  0.925  to  0.930;  saponification  value,  188  to  193;  iodine  value, 
120 ;  Maumene  test,  85°  to  91°  C.  Some  varieties  dry  on  exposure 
to  the  air.  Whale  oil  is  used  for  leather  dressing,  in  tempering 
steel,  and  as  an  illuminating  oil. 

Porpoise  oil,  derived  from  the  porpoise,  Phoccena  brachyciitm,  is 
very  similar  to  whale  oil,  and  is  obtained  in  the  same  way.  Its 
density  is  0.920  to  0.930 ;  saponification  value,  216 ;  it  yields  a 
small  amount  of  elaidin.  The  best  grades  (jaw  oil)  are  used  for 
lubricating  clocks  and  watches,  the  commoner  qualities  for  soap 
stock,  for  leather  dressing,  and  as  illuminating  oil. 

Blackfish  oil  is  obtained  from  the  blubber  of  the  blackfish, 
Globicephalus  melas.  It  is  a  pale  yellow  oil,  which  separates 
spermaceti  (cetyl  palmitate)  011  standing.  That  from  the  head 
and  jaw  is  the  finest  quality,  and  is  used  for  lubricating  clocks 
and  fine  machinery. 

TEKRESTRIAL  ANIMAL   OILS 

These  oils  have  low  iodine  value  and  yield  solid  elaidin.  They 
are  derived  from  the  feet  of  cattle,  horses,  and  sheep,  or  are  ex- 
pressed from  lard  and  tallow. 

Neat's-foot  oil  is  made  by  boiling  the  feet  and  shin  bones  of 
cattle  in  water.  It  is  a  pale  yellow,  limpid  oil  of  0.916  sp. 
gr.  at  15°  C.,  is  nearly  odorless,  and  deposits  stearin  on  stand- 
ing. Its  saponification  value  is  194 ;  iodine  value,  70 ;  it  yields  a 
solid  or  semi-solid  elaidin;  Maumene  test,  47°  to  48.5°  C.  It  is 
nearly  pure  olein,  and  does  not  readily  become  rancid  nor  gummy 
when  used  on  machinery.  It  is  used  for  a  fine  lubricator  and  for 
leather  dressing.  It  is  often  adulterated  with  fish,  rape,  cotton-seed, 
and  mineral  oils,  and  other  hoof  oils. 

Lard  oil  is  prepared  by  cold  pressing  lard  (p.  317).  The  best 
quality  is  limpid  and  colorless,  and  consists  of  olein,  with  some 


316  OUTLINES   OF  INDUSTRIAL   CHEMISTRY 

palmitin  and  stearin,  the  quantity  of  these  latter  depending  upon 
the  temperature  of  the  pressing ;  poor  grades  have  a  brown  color 
and  offensive  odor.  It  has  a  specific  gravity  of  0.915  at  15.5°  C. ; 
a  saponification  value  of  195  to  196;  iodine  value,  56  to  74;  it 
yields  solid  elaidin.  It  is  used  as  an  illuminant,  as  a  lubricant, 
and  for  oiling  wool.  It  is  frequently  adulterated  with  cotton-seed 
oil,  cocoanut  olein,  "  neutral  mineral  oil,"  or  rape  oil. 

Tallow  oil  consists  mainly  of  olein,  and  is  obtained  by  pressing 
tallow  (p.  317).  It  is  chiefly  mixed  with  mineral  oil  for  use  as  a 
lubricant.  If  selected,  fresh  tallow  is  rendered  at  65°  C.,  and  the 
clear  oil  kept  for  twenty-four  hours  in  a  graining  vat,  the  stearin 
and  part  of  the  palmitin  crystallize.  By  pressing,  the  liquid  olein 
and  some  palmitin  is  obtained  as  "  oleo  oil,"  which  is  used  for  arti- 
ficial butter  making.  Low  grades  of  tallow  oil  are  not  white,  and 
are  called  "  red  oil "  in  trade ;  these  must  not  be  confounded  with 
the  red  oil  which  consists  of  oleic  acid  (p.  330).  The  press-cake 
(chiefly  stearin)  is  used  as  a  soap  or  candle  stock. 

SOLID   VEGETABLE  FATS 

Palm  oil  is  obtained  from  the  fruit  of  several  varieties  of  palm, 
Elceis  Guineensis,  Jacq.,  native  to  the  west  coast  of  Africa.  It  is  a 
mixture  of  palmitic  acid,  palmitin,  and  olein,  and  is  semi-solid  in 
this  climate.  When  fresh  it  is  red  or  orange  yellow,  but  on  stand- 
ing, especially  if  exposed  to  the  sunlight,  it  becomes  brownish  yel- 
low or  drab.  It  may  be  bleached  by  heating  and  blowing  in  air  ;  or 
by  treating  with  potassium  bichromate  and  hydrochloric  acid. 
Fresh  oil  has  a  pleasant  odor,  but  is  very  liable  to  become  rancid, 
when  it  contains  a  large  percentage  of  fatty  acids  and  has  a  disagree- 
able odor.  Its  specific  gravity  is  0.920  to  0.946 ;  the  saponification 
value  is  196  to  202 ;  iodine  value,  50.4  to  52.3.  It  is  used  as  a  candle 
and  soap  stock,  and  in  making  lubricants. 

Palm  kernel,  or  palm  nut  oil  is  derived  from  the  kernels  of  the 
fruit  of  Elceis  Guineensis,  Jacq.  It  is  similar  to  and  used  in  the 
same  way  as  cocoanut  oil. 

Cocoanut  oil  is  derived  from  the  cocoanut,  Cocos  nucifera,  L.  (or 
butyracea,  L.  f.),  the  chief  commercial  supply  coming  from  India, 
Ceylon,  and  the  South  Sea  Islands.  The  dried  meat  ("  copra ") 
of  the  nut  is  pressed  or  boiled  in  water.  The  oil,  which  is  a  solid 
fat  in  this  climate,  contains  the  glycerides  of  myristic,  palmitic, 
stearic,  lauric,  capric,  caprylic,  and  caproic  acids.  It  melts  at  20°  to 
28°  C. ;  its  saponification  value  is  250  to  268 ;  its  iodine  value,  8.9. 


VEGETABLE  AND   ANIMAL  OILS  317 

It  is  very  liable  to  become  rancid.  It  is  much  used  for  soap  stock, 
especially  for  the  "  cold  process  "  soaps,  and  since  it  is  not  readily 
precipitated  by  salt,  for  marine  soaps ;  but  it  needs  a  strong  lye  for 
its  saponification.  It  is  also  said  to  be  used  for  artificial  butter. 
By  cold  pressing,  a  solid  stearin  is  obtained  which  is  used  in  mak- 
ing candles. 

Cacao-butter  is  obtained  from  the  cacao  bean,  the  seeds  of 
Tliebroma  Cacao,  L.,  and  is  a  solid  fat  having  a  pleasant  odor  and 
the  flavor  of  chocolate.  It  consists  of  the  glycerides  of  palmitic, 
stearic,  and  lauric  acids,  with  traces  of  linoleic  and  arachidic  acids. 
It  is  used  for  ointments  and  salves  in  pharmacy,  and  in  the  manu- 
facture of  "chocolate  creams,"  and  for  toilet  soaps.  It  is  often 
adulterated  with  tallow,  vegetable  oils,  beeswax,  or  paraffine  wax. 
Its  specific  gravity  is  0.890  to  0.900  at  15°  C. ;  saponification  value, 
192  to  202 ;  iodine  value,  32  to  37.7. 

Japan  wax  is  obtained  from  a  species  of  Rlius  by  boiling  the  fruit 
in  water.  It  is  a  pale  yellow  or  white,  has  a  greasy  feel,  and  can 
be  kneaded  in  the  fingers.  It  consists  of  palmitin,  C3H5(C16H3102)3, 
with  some  stearin,  and  is  easily  saponified.  It  is  not  a  true  wax. 
It  melts  at  53°  to  54°  C.,  and  its  specific  gravity  is  0.970  to  0.980  at 
15°  C.  It  is  soluble  in  benzene,  petroleum  spirit,  and  in  boiling  97 
per  cent  alcohol.  It  is  used  for  candles,  for  wax  matches,  as  a  fur- 
niture polish,  and  for  adulterating  beeswax. 

SOLID   ANIMAL   FATS 

Lard  is  prepared  from  the  fat  of  the  hog.  It  is  rendered  at  a  low 
temperature,  and  is  a  softer  grease  than  tallow.  It  is  a  mixture  of 
palmitin,  stearin,  and  olein.  It  melts  at  28°  to  45°  C.,  forming  a 
clear  liquid.  Its  specific  gravity  is  about  0.932;  saponification 
value,  195  to  196;  iodine  value,  59;  Maumene  test,  24°*to  27°  C. 
When  pure,  it  is  white,  nearly  odorless  and  tasteless.  By  pressing 
it  yields  lard  oil  (p.  315).  It  is  often  adulterated  with  water,  25 
per  cent  or  even  more  being  worked  into  it ;  or  with  cotton-seed  oil 
and  stearin ;  or  with  beef  fat  and  cocoanut  oil.  The  chief  uses  of 
lard  are  for  culinary  purposes,  for  soap  stock,  for  butterine,  and  in 
ointments  and  salves.  "  Compound  lard "  is  a  mixture  of  beef 
stearin  and  cotton-seed  oil. 

Tallow  is  the  solid  fat  of  the  sheep  or  ox.  Before  rendering,  it 
is  customary  to  break  up  the  tissues  by  grinding  with  hollow  rolls 
having  a  rough  surface  and  heated  by  steam.  The  rendered  tallow 
solidifies  at  about  34°  to  45°  C.,  and  is  graded  according  to  its  ap- 


818  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

pearance,  hardness,  odor,  and  rancidity.  It  consists  of  abont  two- 
tliirds  palmitin  and  stearin,  and  one-third  olein.  Its  density  at 
99°  C.  is  0.860  to  0.862 ;  saponification  value,  195  to  198 ;  iodine  value, 
40.  It  is  extensively  used  for  soap  and  candle  stock,  for  lubricating, 
and  as  a  leather  dressing. 

Bone  tallow  is  a  soft  grease  obtained  by  boiling  fresh  bones  in 
water  to  extract  the  marrow  and  fat.  It  is  dark-colored  and  foul- 
smelling  and  usually  contains  calcium  phosphate.  It  is  mainly  used 
for  cheap  colored  soaps. 

Butter  fat  is  derived  from  cows'  milk.  It  is  very  complex, 
containing  glycerides  of  a  number  of  acids  ^of  which  oleic  (60  per 
cent),  palmitic,  stearic,  and  butyric  (5  per  cent)  are  the  most  im- 
portant; small  quantities  of  the  glycerides  of  capric  and  caproic 
acids  are  also  present.  Butter  fat  has  a  specific  gravity  of  0.870  at 
99°  C. ;  its  saponification  value  is  221  to  227 ;  iodine  value,  26  to  35. 
It  is  the  basis  of  butter,  of  which  it  forms  about  90  per  cent,  the  re- 
mainder being  water,  salt,  curds,  and  coloring  matter.  It  is  made 
by  churning  cream  to  cause  the  agglomeration  of  the  fat  globules 
into  a  solid  mass.  Sour  cream  churns  more  easily  than  sweet  cream. 
The  latter  is  removed  from  the  milk  by  a  separator  *  or  by  skim- 
ming before  the  milk  sours.  Butter  from  sour  cream  will  not  keep 
unless  well  salted,  since  it  contains  sufficient  casein  to  increase  its 
liability  to  become  rancid,  by  which  a  considerable  amount  of  butyric 
acid  is  formed.  Butter  is  usually  colored  with  carrot  juice,  saifron, 
turmeric,  or  annato ;  or  sometimes  with  certain  coal-tar  colors. 

Butterine,  oleomargarine,  and  margarine  are  butter  substitutes 
made  from  mixtures  of  animal  and  vegetable  oils,  flavored  with  some 
butter,  and  colored  to  imitate  it.  Oleo  oil  from  tallow,  and  neutral 
lard  are  much  used.  These  are  mixed  with  cotton-seed  oil  in  cold 
weather  (or  with  peanut  or  sesame  oil  abroad)  to  increase  the  per- 
centage of  olein. 
. 

B.   WAXES 

I.   LIQUID   WAXES 

Sperm  oil  is  obtained  from  the  blubber  and  head  cavity  ("  case  ") 
of  the  cachalot,  or  sperm  whale,  Physeter  macrocephalus,  the  case 
alone  sometimes  yielding  several  barrels  of  free  oil.  The  composition 

*  Before  churning,  sweet  cream  is  always  allowed  to  "ripen";  i.e.  to  stand  a 
few  hours  undisturbed  after  separating.  Usually  a  "  starter"  is  added  to  set  up 
lactic  fermentation ;  by  using  pure  cultures  of  acid-forming  bacteria,  the  quality  and 
flavor  of  the  butter  can  be  much  better  controlled  than  when  the  ripening  is  spon- 
taneous. 


WAXES  319 

of  sperm  oil  is  not  definitely  known,  but  it  differs  materially  from 
most  oils.  It  contains  no  glycerides,  consisting  mainly  of  esters  of 
monatomic  alcohols.  Some  authorities  hold  that  dodecatyl  alcohol 
C^HasOH,  and  its  allied  homologues,  such  as  cetyl  alcohol,  C^H^  •  OH, 
are  present,  but  this  is  denied  by  Lewkowitsch.  The  oil  holds  in 
solution  a  considerable  amount  of  spermaceti  (below),  which  is  usually 
filtered  out  of  the  cold  oil  before  it  is  sold.  Sperm  oil  is  a  limpid, 
golden  yellow  liquid,  having  a  slight  fishy  odor;  its  specific  gravity 
is  0.875  to  0.884  at  15.5°  C. ;  saponification  value  123  to  147 ;  iodine 
value  81.3  to  85 ;  it  yields  a  solid  elaidin ;  Maumene  test  45°  to  47°  C. 
It  is  a  very  valuable  lubricator,  especially  for  rapid  running  machin- 
ery, since  its  viscosity  is  very  great  considering  its  low  density,  and 
varies  but  little  with  changes  of  temperature ;  and  because  it  does 
not  become  gummy  nor  rancid.  It  is  also  used  for  illuminating,  for 
leather  dressing,  and  in  tempering  steel.  Because  of  its  high  price, 
it  is  often  adulterated  with  mineral  oils  or  with  other  fish  oils. 
The  related  Doegling  or  Bottlenose  oil  is  also  a  liquid  wax. 


II.    SOLID   ANIMAL   WAXES 

Spermaceti  is  a  crystalline  wax  found  in  the  head  of  the  sperm 
whale  and  which  separates  from  sperm  oil  when  chilled ;  it  is  ob- 
tained by  expressing  the  oil.  The  brown  or  yellow  scales  of  crude 
spermaceti  are  treated  with  a  little  caustic  potash  to  remove  adher- 
ing oil,  and  are  thus  rendered  white  and  translucent  while  they  re- 
tain their  crystalline  structure.  Spermaceti  consists  mainly  of  cetyl 
palmitate,  C^H^O  •  C16H310.  It  is  odorless  and  tasteless  and  melts 
at  about  45°  C.  Its  specific  gravity  is  0.943  at  15°  C. ;  saponification 
value  108  to  128 ;  it  burns  with  a  large  clear  flame.  Its  chief  uses 
are  in  candle  making,  in  confectionery,  and  in  pharmacy. 

Beeswax  is  obtained  from  the  honey-comb  of  bees  by  melting  it 
in  hot  water ;  the  floating  layer  of  tough  brown  or  yellow  wax  is 
drawn  off  into  moulds.  It  may  be  bleached  by  exposure  in  thin 
films  to  the  sun  and  moist  air,  or  by  the  moderate  action  of  chromic 
or  nitric  acid,  or  hydrogen  peroxide.  Bleached  wax  is  white,  and 
has  neither  taste  nor  smell.  It  consists  mainly  of  myricyl  palmitate, 
C3oH610  •  C]6H310,  and  some  cerotic  acid,  C^R5402.  It  melts  at  63°  to 
64°  C.,  and  has  a  specific  gravity  of  0.965  to  0.969  at  15°  C.  It  is 
often  adulterated  with  water  or  white  mineral  powders  to  increase 
its  weight.  Stearin,  paraffine,  cerasin,  tallow,  and  vegetable  wax  are 
often  added  as  adulterants.  It  is  used  in  candle  making,  in  phar- 
macy, and  for  many  other  purposes  in  the  arts. 


OUTLINES  OF  INDUSTRIAL   CHEMISTRY 

Chinese  wax,  or  insect  wax,  is  secreted  by  an  insect,  Coccus  ceri- 
ferus,  Fabr.  The  wax  is  deposited  on  the  branches  of  certain  trees, 
which  are  cnt  off  and  the  wax  removed  by  hand.  It  is  melted  in 
boiling  water  to  separate  the  dirt,  bark,  etc.  It  is  white,  crystalline, 
and  very  hard,  without  taste  or  smell.  It  is  soluble  in  benzine,  and 
slightly  so  in  alcohol  and  ether.  It  consists  of  ceryl  cerotate, 
C^H^O-C^HsA  Its  specific  gravity  is  0.970  at  15°  C.,  and  it  melts 
at  82°  to  83°  C.  It  is  used  for  fine  candles,  in  medicine,  as  size  for 
paper,  and  as  a  furniture  polish. 

Wool  grease  is  the  greasy  substance  exuding  with  the  perspi- 
ration from  sheep ;  it  is  precipitated  by  sulphuric  acid  from  the 
alkaline  waters  in  which  the  raw  wool  has  been  washed ;  it  is  also 
largely  obtained  by  extracting  raw  wool  with  gasoline.  It  is  yellow 
or  dark  brown,  has  an  unpleasant  odor,  and  forms  an  emulsion  with 
water.  It  is  very  complex  in  composition,  containing  several  gly- 
cerides,  in  addition  to  the  stearic  and  palmitic  ethers  of  choles- 
terin  and  isocholesterin,  and  potassium  salts  of  several  fatty  acids. 
A  large  amount  of  unsaponifiable  matter  is  also  present.  Purified 
wool  grease  has  a  specific  gravity  of  0.973  at  15°  C. ;  saponification 
value  98  to  102.4 ;  iodine  value  25  to  28. 

Lanolin  is  made  by  washing  wool  grease  with  water  until  all  the 
soluble  matter  is  removed,  melting  by  heating  in  water,  skimming 
and  allowing  it  to  cool  and  solidify.  Lanolin  is  much  used  in  phar- 
macy as  a  basis  for  salves,  ointments,  and  emulsions.  It  contains 
about  25  per  cent  of  water,  and  forms  a  very  soft  ointment. 

SOLID   VEGETABLE   WAX 

Carnauba  wax  is  derived  from  a  species  of  palm,  Copernicia  ceri- 
fera,  Mart.,  native  in  Brazil.  It  forms  a  coating  on  the  leaves,  and 
is  removed  by  shaking  or  pounding.  The  raw  wax  is  of  a  grayish 
or  greenish  yellow  and  is  very  hard,  though  readily  powdered. 
When  purified,  it  has  no  odor  nor  taste,  melts  at  83°  to  88°  C.,  and 
has  a  specific  gravity  of  0.990  to  0.999  at  15°  C.  Its  constitution  is 
complex,  but  it  contains  myricyl  cerotate  CgoH^O  •  C^H^O,  myricyl 
alcohol  C30H61OH,  cerotic  acid  C27HS402,  and  other  bodies.  It  is 
used  for  candle  making  and  for  adulterating  beeswax,  and  in  varnish. 

REFERENCES 

Die  Chemie  der  Austrocknenden  Oele.     G.  J.  Mulder,  Berlin,  1867. 
Die  Fettwaaren  und  fetten  Oele.     C.  Lichtenberg,  Weimar,  1880. 
Die  Trocknenden  Oelen.     L.  E.  Andes,  Braunschweig,  1882.     (Vieweg.) 
Technologic  der  Fette  und  Oele.     C.  Schaedler,  Berlin,  1883. 


SOAP  321 

Oils  and  Varnishes.    J.  Cameron,  London,  1886.     (J.  and  A.  Churchill.) 
Commercial  Organic  Analysis.     A.  H.  Allen.     Vol.  II.    London,  1886. 
Das  Wachs  und  seine  technische  Verwendung.     S.  Sedna,  Wein,  1886. 
Animal  and  Vegetable  Fats  and  Oils.     W.  T.  Brannt,  Philadelphia,  1888. 
Die  Fetten  Oele  des  Pflanzen  und  Thierreiches.     G.  Bornemann,  Weimar,  1889. 
Die  Untersuchung  der  Fette,  Oele,  Wachsarten,  u.  s.  w.  •  C.  Schaedler,  Leipzig, 

1890. 

Les  Corps  Gras.    A.  M.  Villon,  Paris,  1890. 
Les  Matieres  Grasses.     G.  Beauvisage,  Paris,  1891. 
Painters'  Colours,  Oils,  and  Varnishes.     G.  H.  Hurst,  London,  1892.     (Griffin 

&  Co.) 

Die  Sclimiermittel.     J.  Grossmann,  Wiesbaden,  1894. 

Oils,  Fats,  and  Waxes.     C.  R.  Alder  Wright,  London,  1894.     (Griffin  &  Co.) 
Chemical  Analysis  of  Oils,  Fats,  and  Waxes.     R.  Benedikt.    Translated  by  J. 

Lewkowitsch.     London,  1895. 
Chemical  Technology.     C.  E.  Groves  and  Wm.  Thorp.     Vol.  II.     Lighting. 

Philadelphia,  1895.     (P.  Blakeston,  Son  &  Co.) 
Analyse  der  Fette  und  Wachsarten.     R.    Benedikt  und  F.  Ulzer,     3te  Auf. 

Berlin,  1897.     (J.  Springer.) 
A  Short  Handbook  of  Oil  Analysis.     A.  H.  Gill,  Philadelphia,    1897.     (Lip- 

pincott  Co.) 

SOAP 

Soaps  are  metallic  salts  of  certain  non-volatile  fatty  acids,  the 
commercial  article  usually  containing  a  mixture  of  several  of  these 
salts.  Soaps  intended  for  washing  purposes  should  contain  only 
soluble  salts  of  the  acids ;  i.e.  those  of  sodium,  potassium  or  ammo- 
nium ;  the  calcium,  magnesium,  lead,  and  other  heavy  metal  soaps 
are  insoluble  in  water. 

As  already  explained,  the  common  fats  and  oils  contain  the  fatty 
acids  in  combination  with  glycerine,  forming  glycerides,  an*  it  is 
from  these  that  soaps  are  generally  made.  The  process  of  decom- 
posing the  glycerides  and  forming  soap  is  called  saporiification, 
although  this  term  is  generally  used  to  denote  the  decomposition  of 
any  organic  ester  into  its  basic  alcohol  and  free  acid.  Saponification 
is  effected  in  several  ways :  — 

(1)  By  the  action  of  water  or  steam  at  high  temperature  or  pres- 
sure :  — 

C3H5  (CMHaA),  4-  3  H20  =  C3H5  (OH),  +  3  C^HgA . 

This  hydrolysis  may  be  accomplished  at  a  much  lower-  tempera- 
ture if  the  water  is  acidulated  with  a  dilute  mineral  acid,,  which 
seems  to  assist  the  action  of  the  water  in  some  way,  without  enter- 
ing directly  into  the  reaction.  The  amount  needed  is  small,  and  it 
is  all  found  unchanged,  mixed  with  the  products,  of  the-  reaction. 


322  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

This  method  is  chiefly  employed  for  the  preparation  of  glycerine  and 
to  obtain  the  free  fatty  acid. 

(2)   By  the  action  of  caustic  alkalies :  — 

C3H5  (C18H3A)3  +  3  NaOH  =  C3H5  (OH)8  +  3  C18H3502  •  Na. 

This  is  the  reaction  employed  in  ordinary  soap  making,  the 
caustic  uniting  with  the  fatty  acid  radical  to  form  the  soap,  i.e.  an 
alkali  salt  of  the  acid.  The  glycerine  formed  is  a  by-product,  and  is 
often  not  recovered  from  the  lye;  but  the  more  progressive  soap 
makers  have  now  added  a  glycerine  recovery  plant  to  their  works. 

The  chemistry  of  saponification  was  first  explained  by  Chevreul, 
who  attributed  the  cleansing  action  of  soap  to  free  alkali  formed  by 
the  decomposition  of  the  soap  when  brought  into  solution.  Krafft 
and  Stern1*  confirm  this,  and  hold  that  in  the  hot  dilute  soap  solu- 
tion, part  of  the  soap  is  dissociated  into  free  acid  and  free  alkali,  but 
on  cooling,  the  free  acid  unites  with  some  of  the  undissociated  neu- 
tral soap,  to  form  insoluble  bi-palmate,  bi-stearate,  or  other  bi-salt, 
leaving  the  free  alkali  in  solution.  The  turbid  appearance  of  the 
solution  may  be  due  to  oily  drops  of  the  free  fat  acid. 

The  alkalies  commonly  used  for  soap  making  are  caustic  potash 
and  soda.  The  former  yields  a  "  soft  soap,"  which  is  liquid  under 
ordinary  conditions,  because  of  the  lower  melting  point,  greater  solu- 
bility, and  possible  deliquescence  of  potassium  soaps.  The  glycerine 
formed  remains  mixed  in  the  soft  soap. 

Previous  to  Leblanc's  invention  of  the  soda  process,  soap  was 
made  with  caustic  potash  derived  from  wood  ashes  and  lime.  Com- 
mon salt  was  added  after  the  saponification  of  the  fat  was  complete, 
forming  hard  sodium  soap,  according  to  the  reaction :  — 

KCwHjA  +  NaCl  =  KC1  +  NaCMH«02. 

But  now  most  soft  soaps  are  made  from  soda  soaps  by  adding  a  large 
quantity  of  water. 

The  fatty  material  (soap  stock)  varies  according  to  the  kind  of 
soap  desired  and  the  facility  with  which  certain  stocks  may  be  ob- 
tained. For  white  soaps,  the  best  grades  of  tallow,  lard,  palm  oil,  or 
cocoanut  oil  are  chiefly  used  in  this  country.  Cotton-seed  oil  is  very 
liable  to  become  rancid  and  to  cause  yellow  or  brown  spots  in  the 
product,  besides  giving  it  a  bad  odor  and  a  greasy  appearance.  Corn 
oil  is  also  subject  to  rancidity.  In  Europe,  Castile  soap  is  made  from 
second  quality  olive  oil,  to  which  some  cocoanut  oil  is  generally 
added. 

*  Berichte  d.  deutschen  chemischen  Gesellschaft,  27,  1747. 


SOAP 


323 


Laundry  soaps  are  made  from  tallow,  bone  grease,  and  house 
grease,  and  often  palm  and  cotton- seed  oils.  Yellow  soaps  are  made 
from  these  materials,  with  the  addition  of  a  certain  proportion  of 
rosin.  The  latter  combines  readily  with  alkali,  but  forms  a  rather 
soft  soap,  with  good  lathering  properties ;  rosin  is  cheaper  than 
most  of  the  fats,  and  when  used  in  proper  quantities,  adds  certain 
valuable  properties  to  the  soap,  and  is  not  an  adulterant. 

The  non-drying  oils,  with  caustic  soda,  generally  yield  the  hard- 
est soaps,  while  the  semi-drying  and  drying  oils  form  products  of 
butter-like  consistency. 

Cocoanut  oil  saponifies  readily  with  strong  lye,  without  boiling ; 
hence  is  used  for  "cold  process"  soaps.  "German  mottled,"  or 
"olein  soaps,"  are  made  from  crude  oleic  acid  ("red  oil"),  obtained 
in  the  candle  industry  (p.  330).  The  spent  lyes  from  white  or  yel- 
low soaps  are  often  used  in  making  red-oil  soap,  in  order  to  save  all 
the  alkali,  since  the  oil  will  combine  with  the  carbonate  as  well  as 
with  the  caustic. 

Toilet  soaps  should  be  made  from  the  best  material,  but  many 
cheap  grades  are  made  from  poorer  stock  than  laundry  soap,  and  the 
defects  covered  by  high  color  and  perfume.  Some  toilet  soaps  are 
made  by  melting  together  two  or  more  kinds  of  soap. 

Good  soap  cannot  be  made  from  poor  material.  The  lye  must  be 
a  caustic  liquor,  free  from  other  salts,  sulphides  and  sulphites  being 
especially  injurious,  since  they  cause  discoloration  of  the  soap.  In 
many  large  works  the  lye  is  prepared  by  causticizing  soda-ash  with 
lime.  When  caustic  is  purchased,  it  is  simply  dissolved  to  form  a 
solution  of  the  desired  strength,  varying  from  18°  to  30°  Be. 


Fio.  82. 


Soap  kettles  are  square  or  round,  and  vary  in  size  from  10  feet  in 
diameter  by  15  feet  deep,  to  25  by  35  feet,  and  capable  of  holding 
300,000  pounds  of  soap.  In  modern  factories  they  are  always  heated 
by  steam ;  very  small  ones,  used  for  remelting  toilet  soaps,  etc.,  being 


324  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

steam-jacketed,  and  the  larger  ones  having  both  open  and  closed 
coils.  A  modern  form  (Fig.  82)  has  a  conical  bottom,  in  which  the 
steam  coils  (A,  B)  are  arranged.  Such  a  kettle,  calculated  to  hold 
100,000  pounds  of  soap,  is  about  15  feet  in  diameter  and  21  feet 
high,  the  cone  bottom  being  about  5  feet  deep,  and  the  cylindrical 
walls  about  16  feet  high.  It  is  made  of  f-inch  boiler  plate,  and  is 
sheathed  with  2-inch  pine  staves.  It  rests  on  stone  pillars  and 
foundations,  and  has  large  draw-off  cocks  in  the  cone,  for  running 
off  waste  lyes  while  the  soap  is  pumped  away  through  a  pipe  (D) 
passing  through  the  side  of  the  kettle- 
Soaps  are  made  by  various  processes,  but  the  most  common  are 
the  following :  — 

(1)  The  fat  is  treated  with  the  exact  amount  of  caustic  alkali 
needed  to  saponify  it,  leaving  the  glycerine  in  the  soap.    The  so-called 
"cold  process"  soap  is  the  most  common  example  of  this  method. 

(2)  The  fat  is  boiled  with  solutions  of  caustic  alkali  until  saponi- 
fication  is  complete,  or  until  the  soap  attains  certain  desired  proper- 
ties.    The  glycerine  remains  mixed  with  the  product,  as  in  the  case 
of  soft  and  " marine"  soaps;  or  it  is  excluded,  as  in  the  case  of  yel- 
low, laundry,  mottled,  and  curd  soaps. 

(3)  A  free  fatty  acid  is  neutralized  by  treatment  with  an  alka- 
line hydroxide  or  carbonate,  as  in  the  case  of  oleic  acid. 

The  cold  process  is  the  simplest  of  soap-making  methods,  but 
requires  carefully  calculated  quantities  of  caustic  and  fat,  and  the 
latter  must  be  well  refined.  Since  it  is  difficult  to  calculate  the 
exact  amount  of  alkali,  such  soaps  usually  contain  free  fat  or  free 
alkali,  or  both.  Cocoanut  oil  and  tallow  are  chiefly  used,  and  are 
melted  and  run  into  a  mixing  tank  heated  by  steam,  or  into  a 
crutcher  (p.  325).  Then  a  definite  quantity  of  strong  caustic  soda 
lye,  32°  to  36°  Be.,  is  added,  and  the  mixture  well  stirred  for  a  few 
minutes.  The  heat  of  the  reaction  is  sufficient  to  carry  it  on  when 
once  started.  After  saponification  is  well  under  way,  the  stirring  is 
stopped  and  the  mixture  is  run  into  " frames"  (p.  326),  where  it 
stands  several  days,  to  complete  the  reaction  and  to  cool.  This 
leaves  all  the  glycerine  and  any  excess  lye  in  the  soap.  The  product 
looks  well  when  fresh,  but  is  very  apt  to  turn  yellow  and  become 
rancid. 

Most  soaps  are  boiled.  The  process  is  usually  divided  into 
several  stages.  The  melted  fat  and  lye  of  about  15°  Be.  (1.115  sp. 
gr.)  are  run  into  the  soap  kettle  together,  while  free  steam  is  blown 
in  to  mix  them,  and  to  form  an  emulsion  of  the  oil  and  lye,  which  is 
essential  to  the  beginning  of  saponification,  or,  as  the  soap-boiler 


SOAP  325 

terms  it,  "to  kill  the  stock."  When  the  emulsion  forms,  the  lye  has 
"  caught  the  stock."  If  the  lye  is  too  strong  at  first,  it  does  not 
"  catch,"  and  water  is  added  and  the  heating  continued  until  the 
emulsion  forms.  Strong  lye  is  then  carefully  added  in  small  por- 
tions at  a  time,  and  boiling  is  continued  to  complete  the  saponifica- 
tion.  If  a  wooden  stirring  paddle  be  pushed  into  the  mass  at  this 
time  the  soap  adheres  to  it  when  drawn  out,  and  long  strings  of 
soap  hang  down  from  it.  There  is  no  separation  of  the  lye.  When 
the  process  is  finished,  as  is  shown  by  the  soap  having  a  dry,  firm 
feel  between  the  fingers,  the  soap  is  " grained"  or  "salted  out,"  by 
adding  common  salt.  This  causes  a  separation  of  the  soap  from  the 
lye  and  glycerine,  which  is  shown  by  the  soap  sticking  to  the  paddle 
while  the  lye  runs  off.  When  properly  salted,  the  soap  boils  in 
broad,  smooth  patches,  and  is  hard,  and  not  sticky,  when  cold.  The 
steam  is  then  cut  off  and  the  soap  allowed  to  stand  for  several  hours, 
when  it  rises  to  the  top.  The  salt  lye,  which  contains  most  of  the 
glycerine,  is  drawn  off,  leaving  the  soap  in  the  kettle.  Strong  lye, 
25°  Be.  (1.205  sp.  gr.)  is  now  added,  and  for  yellow  soaps,  rosin  is 
introduced ;  for  white  soap,  tallow  or  cocoanut  oil  are  used  instead 
of  the  rosin.  The  boiling  is  continued  for  two  or  three  days,  until 
the  soap  becomes  clear  and  semi-transparent.  This  second  boiling 
is  called  the  "  rosin  change  "  or  the  "  strong  change  " ;  during  this 
time,  the  soap  rises  fully  one-third  the  depth  of  the  kettle,  and  often 
stands  higher  than  its  sides.  For  this  reason,  the  kettle  is  not  filled 
more  than  two-thirds  full  at  first.  When  the  rosin  or  cocoanut  oil 
is  saponified,  the  kettle  is  allowed  to  stand  quietly  for  a  number  of 
hours,  when  the  lye  is  drawn  off.  The  next  step  is  called  "  finish- 
ing," "settling,"  "pitching,"  or  "fitting."  Water  is  added  to  the 
boiling  soap  until  it  loses  its  granular  appearance,  after  which  it 
is  allowed  to  settle  for  several  days.  This  removes  excess  caustic 
and  any  insoluble  impurities.  The  contents  of  the  kettle  separate 
into  three  layers,  the  soap  on  top,  and  the  lye  at  the  bottom,  and 
between  them  a  dark-colored  layer,  called  "nigre,"  containing  caustic 
lye,  soap,  water,  and  various  organic  impurities. 

The  lye  and  nigre  are  drawn  off  into  separate  tanks,  and  the  soap 
is  pumped  into  the  crutcher,  which  is  a  very^  efficient  mixing  ma- 
chine. One  form  (Fig.  83)  consists  of  a  broad,  vertical  screw,  work- 
ing within  a  cylinder,  which  is  placed  in  a  larger  tank.  The  action 
of  the  screw  draws  the  liquid  soap  in  at  the  bottom  and  discharges  it 
over  the  top  of  the  cylinder,  to  again  pass  through  the  apparatus. 
A  very  thorough  mixing  is  thus  secured. 

The  perfume,  and  any  filling  material,  such  as  silicate  of  sodium, 


326 


OUTLINES  OF  INDUSTRIAL  CHEMISTRY 


sodium  carbonate,  borax,  talc,  etc.,  are  added  in  the  crutcher.  These 
ingredients  are  well  mixed  with  the  soap,  which  becomes  lighter 
colored,  and  then  stiff  and  thick.  After  crutching  for  from  3  to  15 
minutes,  the  soap  is  run  into  "  frames  "  (Fig.  84),  which  are  large 
sheet-iron  boxes,  mounted  on  wheels,  and  having  removable  sides. 


PIG.  88. 


FIG.  84. 


Each  frame  holds  from  1000  to  1700  pounds,  or  one  crutcher  full. 
When  it  has  solidified,  after  24  to  36  hours,  the  sides  are  removed, 
and  the  block  of  soap  stands  several  days  in  the  air  to  cool  thor- 
oughly. Then  it  goes  to  the  "slabber"  (Fig.  85),  a  machine  contain- 
ing a  number  of  tightly  stretched  steel  wires,  which  are  pushed 
against  the  block  of  soap,  cutting  it  into  slabs  of  the  desired  thick- 
ness. These  then  pass  through  a  "  cutter,"  a  similar  machine,  which 
forms  them  into  rough  bars,  which  are  put  into  the  dry  room,  kept 
at  a  temperature  of  about  90°  F.,  for  12  to  15  hours.  They  are  then 
run  through  the  press  which  forms  the  commercial  bar  and  stamps 
on  it  the  trade  mark,  name,  or  other  design.  They  finally  pass  on  an 
endless  belt  to  the  wrappers,  who  enclose  them  in  separate  papers 
and  pack  them  in  boxes,  which  are  immediately  nailed  up  for 
market. 

"  Boiled-down  soap  "  is  made  by  treating  the  soap,  after  the  lye 
has  been  drawn  off,  with  strong  brine,  and  then  boiling  it  down. 
Sometimes  the  soap  is  settled  and  the  nigre  and  lye  separated  before 
boiling  down.  This  reduces  the  percentage  of  water  in  the  soap, 
leaving  it  dry  and  hard.  If  soaps  in  which  no  rosin  is  used  are 


SOAP 


327 


boiled  down  on  the  lye  until  the  latter  becomes  concentrated  enough 
to  precipitate  the  soap,  and  then  run  into  frames  and  cooled  very 
slowly,  the  small  quantity  of  lye  and  other  impurities  mechanically 
enclosed  segregate  during  the  cooling  into  those  parts  of  the  mass 
which  are  the  last  to  solidify,  and  cause  the  appearance  called 


FIG.  85. 


"mottling."  By  adding  a  small  amount  of  copperas,  ultramarine, 
lampblack,  or  other  pigment,  the  mottling  becomes  more  promi- 
nent. Castile  or  Marseilles  soaps  have  a  green  mottle,  changing 
to  red  on  exposure  to  the  air.  This  is  due  to  the  presence  of  cop- 
peras, which  precipitates  the  ferrous  hydroxide  with  the  lye  in  the 
soap;  on  contact  with  the  air,  the  green  hydroxide  is  changed  to 
the  red  ferric  salt.  Rosin  produces  a  more  uniform  soap,  without 
mottle. 

Toilet  soaps  are  made  in  the  same  general  way  as  the  yellow 
soap,  but  from  finer  stock  and  with  greater  care  to  secure  the  com- 
plete removal  of  free  alkali.  A  little  unsaponified  fat  is  better  than 
excess  alkali. 


328  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

Three  classes  of  toilet  soaps  are  made,  —  milled,  remelted,  and 
transparent.  Milled  soaps  are  made  by  shaving  very  thoroughly 
dried  bars  of  good  soap  to  fine  chips,  and  drying  again  until  only 
about  10  per  cent  water  remains.  The  dried  soap  is  then  ground 
in  an  edge-runner  mill,  and  the  perfume  and  any  ether  ingredients 
desired  are  added  at  the  same  time.  After  thorough  incorporation, 
the  soap  is  forced  through  a  die  plate  by  heavy  pressure,  forming  a 
long  bar,  which  is  cut  into  cakes;  these  are  stamped  and  pressed 
into  the  desired  shape.  This  process  allows  the  use  of  very  delicate 
perfumes  and  other  ingredients  which  would  be  destroyed  by  heat. 
It  also  furnishes  a  hard  cake  which  does  not  wear  away  so  rapidly 
when  in  use. 

Remelted  soaps,  chiefly  made  in  England,  are  prepared  by  re- 
melting  one  or  more  kinds  of  soap,  together  with  the  perfumes  and 
other  ingredients,  in  a  steam-jacketed  kettle.  By  rapid  agitation 
of  the  melted  mass  with  paddles,  air  bubbles  can  be  disseminated 
through  the  soap,  which  gives  the  cake  sufficient  buoyancy  to  float 
on  water  after  stamping. 

Transparent  soaps  may  be  made  in  two  ways :  (a)  A  common 
soap  is  dissolved  in  alcohol,  the  solution  decanted  from  insoluble 
impurities,  and  the  alcohol  distilled  off,  leaving  the  soap  as  a  trans- 
parent jelly,  which  is  carefully  dried  in  moulds  to  form  the  cake. 
(6)  A  cold-process  soap  is  made  by  letting  the  fatty  material  stand 
with  the  lye  until  saponified,  the  coloring  matter,  perfumes,  etc., 
having  also  been  stirred  in.  The  glycerine  formed,  remaining  in 
the  soap,  causes  the  latter  to  have  a  translucent  appearance.  By 
adding  more  glycerine,  with  a  little  alcohol,  or  a  solution  of  cane 
sugar,  the  transparency  is  increased. 

Special  scouring  soaps  for  cleaning  metal  and  unpainted  wood- 
work are  made  by  adding  powdered  sand,  glass,  or  pumice-stone  to 
a  yellow  soap.  Strongly  alkaline  soaps  often  contain  ground  soda- 
ash,  borax,  and  sodium  silicate  as  "fillers,"  or  frequently  as  in- 
tentional adulterants.  Sodium  silicate  is  very  generally  added  to 
yellow  soaps,  as  it  hardens  them  somewhat  and  also  possesses  de- 
tergent properties  itself. 

A  few  insoluble  soaps  of  the  heavy  metals  are  prepared  for  use 
in  pharmacy,  the  most  important  being  lead  soap  or  "lead  plaster," 
which  is  made  by  decomposing  a  neutral  soap  with  a  soluble  lead 
salt,  or  by  heating  olive  oil  with  a  paste  of  lead  oxide  in  water. 


CANDLES  329 


CANDLES 

The  materials  used  for  candles  are :  free  fatty  acids,  especially 
palmitic  and  stearic ;  hydrocarbons,  such  as  paraffine  and  ozokerite ; 
and  certain  esters  of  the  fatty  acids,  especially  tallow  and  waxes. 
The  requisites  for  candle  stock  are,  that  it  shall  burn  freely  without 
smoke  or  smell ;  that  it  shall  not  soften  at  so  low  a  temperature 
that  it  loses  its  form  from  the  heat  of  its  own  flame ;  and  that  when 
melted  it  shall  be  a  fluid  capable  of  being  drawn  into  the  wick 
by  capillarity.  Some  glycerides,  such  as  tallow,  burn  with  a  foul- 
smelling,  smoky  flame,  and  hence  are  only  used  in  the  cheapest 
candles.  Also,  they  soften  at  too  low  a  temperature,  and  the  can- 
dle readily  bends  and  gutters.  Both  these  objections  also  apply 
to  paraffine  and  to  some  of  the  solid  fatty  acids. 

Candles  are  made  by  dipping,  pouring,  and  moulding.  For 
dipped  candles,  the  wick  is  repeatedly  introduced  into  the  melted 
stock,  each  layer  of  fat  being  allowed  to  solidify  before  the  next 
dip.  Tallow  dips,  the  poorest  candle  made,  are  prepared  in  this 
way. 

Poured  candles  are  made  by  pouring  the  melted  stock  in  a  slow 
stream  over  the  wick,  which  is  stretched  in  a  frame.  This  method 
is  used  for  wax  candles,  since  the  wax  contracts  too  much  on  cooling 
to  allow  casting.  While  still  plastic,  they  are  rolled  on  a  flat  table 
under  a  board,  to  give  them  a  uniform  diameter. 

Most  candles  are  now  moulded  in  a  cylindrical  metal  form  through 
which  the  wick  is  drawn  in  the  line  of  its  axis.  The  mould  can  be 
surrounded  .with  hot  or  cold  water  to  facilitate  the  casting  and 
removal  of  the  candles.  Wicks  are  of  plaited  or  twisted  cotton 
yarn,  usually  flat,  except  for  tallow  dips,  when  they  are  round. 
They  are  so  prepared  that  the  end  curls  over  and  burns  off  as  the 
candle  is  consumed,  thus  making  snuffing  unnecessary ;  *  also,  they 
are  often  treated  with  ammonium  phosphate  or  borate  to  prevent 
their  smouldering  and  emitting  bad  odors  when  the  candle  is 
extinguished. 

Paraffine,  ozokerite,  and  sperm  candles  (from  spermaceti)  are 
moulded.  In  order  to  prevent  softening  at  too  low  a  temperature, 
and  to  render  them  less  brittle  when  handled,  a  little  stearic  acid  is 
usually  added. 

*  This  is  accomplished  in  several  ways ;  one  side  of  the  wick  may  be  dipped  in 
size,  or  one  thread  be  drawn  a  little  tighter  than  the  rest. 


330  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

The  most  important  candle  stocks  are  palmitic  and  stearic  acids 
and  paraffine  wax. 

Palmitic  and  stearic  acids  are  usually  made  from  tallow  or  palm 
oil  by  saponifying  with  lime,  or  water,  the  hydrolysis  with  the  latter 
being  often  assisted  by  the  addition  of  a  little  acid.  Saponincation 
with  lime  is  carried  on  in  two  ways  :  (a)  by  boiling  in  open  vessels 
with  about  16  per  cent  of  lime.  The  resulting  insoluble  lime  soap 
consists  of  calcium  oleate,  palmitate,  and  stearate.  It  is  separated 
from  the  lye  and  free  glycerine  which  is  also  formed,  and  is  decom- 
posed by  treatment  with  sulphuric  acid  and  steam,  setting  free  the 
fatty  acid,  (b)  Or  the  fat  may  be  saponified  by  Milly's  process ;  i.e., 
boiled  in  closed  vessels  called  autoclaves,  under  pressure  of  from 
8  to  10  atmospheres,  with  from  2  to  4  per  cent  of  lime.  The  latter 
probably  merely  starts  the  hydrolysis,  which  is  finished  by  the 
steam  and  water  present.  The  products  of  the  reaction  are  lime 
soap,  free  fatty  acid,  and  glycerine.  The  turbid  mixture  is  treated 
hot  with  just  sufficient  sulphuric  acid  to  decompose  the  lime  soap. 
The  calcium  precipitates  as  sulphate,  while  on  top  of  the  water 
(which  contains  the  glycerine)  is  a  layer  of  fatty  acid.  This  is 
skimmed  off  and  treated  with  water  acidulated  with  sulphuric  acid 
to  insure  complete  decomposition  of  the  lime  soap. 

The  melted  fatty  acids  obtained  by  either  of  these  processes  are 
run  into  shallow  pans  and  allowed  to  stand  a  few  days  at  a  tem- 
perature of  about  30°  C.,  when  the  palmitic  and  stearic  acids  crys- 
tallize. The  magma  is  first  pressed  cold,  and  then  at  40°  C.,  in  bags 
in  a  hydraulic  press ;  the  liquid  oleic  acid  separated  forms  the  com- 
mercial "red  oil"  or  "olein"  employed  for  soap  stock;  the  solid 
fatty  acids  compose  the  candle  stock  which  is  called  "  stearin."  *  It 
melts  at  52°  to  55°  C.  The  yield  from  tallow  or  palm  oil  is  44  to 
48  per  cent  stearin. 

Saponification  by  water  alone  is  accomplished  by  heating  the  fat 
in  an  autoclave  with  water  to  about  200°  C.  under  pressure  of  about 
15  atmospheres.  A  current  of  superheated  steam  is  introduced, 
thus  thoroughly  mixing  the  contents  of  the  vessel.  The  free  fatty 
acid  and  the  glycerine  both  distill  over  with  the  steam,  the  former 
condensing  in  the  first  receiver,  while  the  latter  passes  on  to 
another.  This  process  needs  much  care  in  the  regulation  of  the 
heat  and  to  secure  the  complete  decomposition  of  the  glycerides,  but, 
when  properly  worked,  yields  very  pure  products.  The  fatty  acids 
are  chilled  and  pressed  as  above  described,  to  separate  the  olein. 

*Not  to  be  confounded  with  the  glyceride  of  stearic  acid,  p.  303. 


CANDLES  331 

The  yield  of  stearin  is  about  50  per  cent  from  tallow  or  palm  oil. 
Slightly  rancid  stock  is  more  easily  decomposed  than  neutral  fat. 

By  adding  from  4  to  5  per  cent  of  strong  sulphuric  acid  to  the 
water  in  the  autoclave,  the  hydrolysis  is  accomplished  at  120°  to 
150°  C.  A  part  of  the  glycerine  is  converted  into  glyceryl-sulphuric 

/OH 

acid,  S(X  ,  while  some  of  the  oleic  acid,  which  is  an 

"\0  -  C3H5(OH)2 

/COOH 
unsaturated  body,  forms  sulpho-stearic  acid,  C17H3/  .     By 

\0  -  S03H 
the  action  of  the  water,  this  is  converted  into  hydroxystearic  acid, 

/COOH 
C^HS/  ,  while  sulphuric  acid  is  regenerated.     The  hydroxy- 

\OH 

stearic  acid  separates  as  a  solid  with  the  free  stearic  and  palmitic 
acids,  and  in  the  subsequent  purification  of  these  by  distillation 
with  superheated  steam,  it  is  decomposed,  separating  more  water 
and  the  residue  polymerizing  to  form  iso-oleic  acid  (C^H^O*,),  a 
solid,  melting  at  45°  C.  Thus  the  yield  of  solid  fat  acids  is  slightly 
increased,  being  about  55  per  cent  from  tallow. 

Another  method  of  acid  saponification  consists  in  heating  the  fat 
with  concentrated  sulphuric  acid  for  a  few  minutes  only,  until  the 
cell  walls  of  the  fat  are  destroyed  and  the  hydrolysis  is  begun.  The 
saponification  is  completed  by  boiling  with  water. 

The  mixed  palmitic,  stearic,  and  oleic  acids  are  chilled  and 
pressed  as  already  described.  Saponification  with  acid  gives  a 
discolored  product,  which  is  usually  purified  by  redistilling  with 
superheated  steam. 

The  liquid  "  olein  "  separated  from  the  fatty  acids  by  any  saponi- 
fication method,  is  of  less  value  than  the  solid  acids.  A  process  for 
producing  palmitic  acid  from  this  oleic  acid  is  based  on  the  fol- 
lowing reaction : 

CigHgA  +  2  NaOH  =  C16H31O2  -  Na  +  C2H302  •  Na  +  H2. 

Caustic  soda  solution  and  oleic  acid  are  heated  together  in  an  iron 
vessel  provided  with  an  agitator,  until  all  the  water  is  evaporated. 
The  heat  is  then  raised  to  a  little  over  300°  C.,  when  the  evolution 
of  hydrogen  becomes  active.  When  the  hydrogen  ceases  to  escape, 
the  product  is  treated  with  water,  which  dissolves  the  sodium  ace- 
tate and  any  undecom posed  caustic,  leaving  sodium  palmitate  undis- 
solved.  This  is  decomposed  with  sulphuric  acid  to  obtain  the  free 


332  OUTLINES  OF   INDUSTRIAL  CHEMISTRY 

fatty  acid.     But  the  product  is  too  soft  and  is   an   unsatisfactory 
candle  stock,  hence  the  method  is  not  now  in  use.* 

After  purification,  the  free  fatty  acids,  obtained  by  any  of  the 
processes  above  described,  are  employed  for  candle  stock.  The 
aqueous  solutions  of  glycerine  ("  sweet  waters  "),  resulting  from  the 
saponification,  are  used  in  the  manufacture  of  pure  glycerine. 

GLYCERINE 

There  are  two  kinds  of  refined  glycerine,  C8H5(OH)3,  on  the 
market,  dynamite  glycerine  and  chemically  pure  glycerine.  These 
differ  only  in  color  and  in  the  content  of  pure  glycerine.  It  is 
largely  recovered  from  the  spent  lyes  from  soap  making  and  from 
the  "  sweet  waters  "  from  the  digesters  where  fats  have  been  saponi- 
fied with  lime  or  with  water  under  pressure.!  Much  crude  candle 
glycerine  is  imported  into  this  country  from  Europe,  that  from 
France,  Italy,  and  Spain  being  derived  from  olive  oil. 

Spent  soap  lyes  are  very  dilute  solutions  of  glycerine  and  con- 
tain much  impurity.  The  successful  recovery  of  glycerine  from 
them  is  one  of  the  recent  triumphs  of  chemical  industry.  The 
Van  Ruymbeke  process  is  the  latest  and  best.  In  this  the  lye  is 
settled  and  drawn  off  from  the  sludge.  It  is  then  treated  with 
a  special  chemical  called  "  persulphate  of  iron,"  the  exact  composi- 
tion of  which  is  not  disclosed,  but  which  contains  about  50  per  cent 
of  sulphuric  acid.  It  is  possibly  a  mixture  of  ferrous  and  ferric 
sulphates.  This  forms  a  copious  precipitate,  consisting  of  ferric 
hydroxide  and  iron  soaps,  which  drags  down  all  other  insoluble 
impurities.  This  precipitate  is  removed  by  filter  pressing  and  the 
clear  liquid  tested  for  any  excess  of  iron  sulphate.  If  any  is  pres- 
ent, it  is  exactly  neutralized  with  caustic  soda  and  the  precipitate 
filtered  off.  This  leaves  the  lye  almost  water  white  and  ready  for 
the  evaporation,  which  is  done  under  high  vacuum  (27  to  28  inches), 
in  a  still,  across  the  middle  of  which  is  a  steam  chest  having  small 
vertical  tubes.  Fresh  lye  is  introduced,  as  the  evaporation  pro- 
gresses, to  maintain  the  level  of  the  liquid.  A  salt-catch  is  placed 
below  the  steam  chest  in  the  evaporator,  and  in  this  the  salt  and 
sodium  sulphate  which  separate,  collect,  and  at  the  end  of  the  opera- 
tion are  removed  through  a  door  in  the  front.  The  salt  thus 
recovered  is  sent  to  the  soap  maker,  to  be  used  again  in  salting  out 
soap. 

*  J.  Soc.  Chem.  Ind.,  1897,  391. 

t  Saponification  with  acid  destroys  much  of  the  glycerine. 


GLYCERINE  333 

The  vapors  from  the  evaporator  pass  through  a  series  of  "  catch- 
alls  "  to  retain  any  lye,  and  then  go  to  a  wet  vacuum  pump,  which  is 
provided  with  a  jet  condenser.  The  evaporation  is  usually  carried 
on  in  two  or  more  stages ;  sometimes  it  is  continued  to  a  point  at 
which  sodium  sulphate  will  crystallize,  which  is  thus  removed;  by 
further  evaporation  in  vacuum,  the  common  salt  is  crystallized. 

When  the  lye  attains  a  density  of  32°  Be.  (1.295  sp.  gr.),  it  con- 
tains about  80  per  cent  of  glycerine,  and  is  called  crude  glycerine. 
This  is  then  distilled  under  a  very  high  vacuum  (28  to  29  inches)  in 
a  still  consisting  of  a  cylindrical  iron  shell  containing  a  closed  steam 
coil  and  a  perforated  pipe,  through  which  superheated  steam  is 
introduced.  The  glycerine  in  the  crude  liquid  passes  over  with  the 
steam  into  coolers,  which  are  simply  cast-iron  drums,  cooled  by  the 
outside  air.  Most  of  the  glycerine  condenses  here,  while  the  uncon- 
densed  steam  and  some  glycerine  passes  on  to  a  surface  condenser. 
The  vacuum  is  maintained  by  a  dry  vacuum  pump.  The  glycerine 
collected  in  the  cooling  drums  is  concentrated  in  vacuum  pans  until 
its  specific  gravity  reaches  1.262.  It  is  then  passed  through  a  filter 
press,  which  removes  any  suspended  dirt,  and  gives  a  clear,  bright 
product.  As  a  rule,  the  glycerine  recovered  from  soap  lye  is  not 
bleached,  and  is  generally  sold  as  dynamite  glycerine. 

Chemically  pure  glycerine  is  made  from  candle  crude  glycerine  by 
the  Van  Ruymbeke  process.  The  crude  liquid,  having  a  density  of 
28°  Be.,  is  diluted,  and  treated  with  milk  of  lime  to  neutralize  any 
acid.  It  is  then  treated  with  a  bleaching  material  known  as  "  black," 
the  composition  of  which  is  kept  secret.  After  filter  pressing,  the 
glycerine  is  concentrated  to  a  density  of  about  31°  Be.,  in  an  appa- 
ratus similar  to  that  used  for  dynamite  glycerine.  It  is  then  distilled, 
as  in  the  case  of  the  latter,  and  the  product  condensing  in  the  cool- 
ers is  thoroughly  bleached  by  treatment  with  more  "  black,"  and  is 
then  filter  pressed.  The  density  of  chemically  pure  glycerine  is  not 
required  to  be  so  high  as  that  of  dynamite  glycerine,  hence  no  final 
concentration  is  necessary.  A  very  fine  grade  of  chemically  pure 
glycerine  is  sometimes  prepared  from  dynamite  glycerine  by  subject- 
ing it  to  the  same  process  employed  for  candle  crude  glycerine. 

Of  the  other  methods  for  recovering  glycerine,  only  the  Glatz  pro- 
cess needs  consideration  here.  In  this  the  lye  is  treated  with  a 
small  amount  of  milk  of  lime,  and  then  all  alkali  neutralized  with 
hydrochloric  acid,  and  the  liquid  filter-pressed  to  remove  the  precipi- 
tated matter.  By  evaporating  the  filtrate  under  a  vacuum,  crude 
glycerine  is  obtained,  which  is  distilled  under  low  vacuum  with 
superheated  steam,  the  still  being  heated  by  direct  fire.  The  prod- 


334  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

uct  is  then  concentrated  in  a  Yaryan  or  similar  evaporator,  until 
heavy  enough  for  market. 

The  yield  of  glycerine  is  always  calculated  on  the  amount  of  fat 
saponified.  By  careful  work,  6.75  per  cent  of  marketable  glycerine 
can  be  obtained  by  the  Van  Ruymbeke  process. 

Glycerine  is  a  thick,  viscid  liquid,  having  a  sweet  taste  and  unc- 
tuous  properties.  It  is  soluble  in  water  and  in  alcohol.  High  grade 
dynamite  glycerine  is  of  a  very  pale,  yellow  color,  odorless,  and  free 
from  acids.  It  contains  no  iron,  lead,  or  calcuim  salts,  and  only  a 
trace  (0.006  per  cent,  at  most)  of  chlorides.  The  ash  is  not  over 
0.01  per  cent.  The  specific  gravity  should  not  be  less  than  1.262  at 
15°  C.  It  is  chiefly  used  in  making  nitroglycerine ;  also  to  some 
extent  as  a  solvent;  in  the  preparation  of  printers'  ink-rolls,  and 
for  increasing  the  body  or  viscosity  of  other  liquids.  Chemically 
pure  glycerine  is  colorless,  containing  less  than  0.009  per  cent  car- 
bonaceous residue,  no  chlorides,  and  leaves  no  ash.  Its  density  is 
about  1.260  sp.  gr.  It  is  largely  used  as  a  preservative  for  tobacco; 
for  confectionery ;  in  pharmacy ;  in  the  preparation  of  cosmetics ;  as 
a  sweetening  agent  in  fermented  drinks,  and  in  preserves;  and 
owing  to  its  non-volatile  and  non-drying  character,  as  an  addition  to 
inks  intended  for  rubber  stamps. 

REFERENCES 

Technology  of  Soap  and  Candles.    K.  S.  Christian!,  Philadelphia,  1881.    (Baird 

&Co.) 

Das  Glycerine.     S.  W.  Koppe,  Wien,  1883.     (Hartleben.) 
Soaps,  Candles,  Lubricators,  and  Glycerine.     W.  L.  Carpenter,  London,  1885. 
The  Art  of  Soap  Making.     A.  Watt,  London,  1887. 
Handbuch  der  Seifenfabrikation.     C.  Diete,  Berlin,  1887. 
Guide  pratique  du  Fabricant  de  Savons.     G.  Calmels  and  E.  Saulnier,  Paris, 

1887. 

Traite"  pratique  de  Savonnerie.     E.  Morride,  Paris,  1888. 
Soaps  and  Candles.     J.  Cameron,  London,  1888.     (Churchill.) 
Manufacture  of  Soaps  and  Candles.     W.  T.  Brannt,  Philadelphia,  1888.     (Baird 

&Co.) 

Seifenfabrikation.     (2  Bander.)     A.  Englehardt,  Wien,  1888. 
Der  praktische  Seifensieder.     H.  Fischer,  Weimar,  1889.     (Voigt.) 
Die  Seifen-Fabrikation.     F.  Wiltner,  Wien,  1891.     (Hartleben.) 
A  Handbook  of  Modern  Explosives.    (Glycerine.)    M.  Eissler,  New  York,  1890. 
Soap  Manufacture.     W.  L.  Gadd,  London,  1893.     (Bell  &  Sons.) 
Savons  et  Bougies.     J.  Lefevre,  Paris,  1894. 

Manufacture  of  Explosives.     (Glycerine.)     O.  Guttmann,  London,  1896. 
Journal  of  the  Society  of  Chemical  Industry,  1839,  4.     O.  Hehner. 
American  Chemical  Journal :  — 

17,  59.     Evans  and  Beach 


ESSENTIAL   OILS  335 

Journal  of  Analytical  and  Applied  Chemistry  :  — 

IV,  147.     J.  F.  Schnaible. 

V,  379.     E.  Twitchel. 

VI,  423.     W.  H.  Low. 
Railroad  and  Engineering  Journal :  — 

65,  495  and  551.     C.  B.  Dudley. 
67,  199  and  251.     C.  B.  Dudley. 


ESSENTIAL  OILS 

The  essential  or  volatile  oils  are  liquids  which  give  the  peculiar 
odors  to  plants.  They  occur  already  formed  in  the  plants,  or  are 
produced  by  the  combination  of  substances  in  the  plant,  which  react 
when  brought  into  the  presence  of  water.  They  have  strong  and 
characteristic  odors  and  pungent  taste,  and  are  generally  volatile 
without  decomposition. 

There  are  three  general  classes  of  these  oils :  (a)  those  containing 
carbon  and  hydrogen  only,  and  which  consist  of  terpenes  of  the 
general  formula  (C10H16)^;  (6)  those  containing  carbon,  hydrogen, 
and  oxygen,  and  mainly  composed  of  ethers,  aldehydes,  ketones,  or 
phenols;  (c)  those  containing  sulphur  or  nitrogen.  The  oils  are 
frequently  mixed  with  solid,  oxygenated  bodies,  called  resins,  which 
have  an  acid  or  anhydride  character.  These  mixtures  are  gener- 
ally called  oleo-resins,  or  balsams. 

The  volatile  oils  are  liquid  at  ordinary  temperatures,  and  are 
usually  nearly  colorless  when  fresh,  but  become  darker  and  thick  on 
exposure.  Many  of  them  are  optically  active.  They  are  nearly 
insoluble  in  water,  though  imparting  their  peculiar  odor  or  taste  to 
it.  They  dissolve  in  alcohol,  carbon  disulphide,  petroleum  ether, 
and  in  fatty  oils.  Excepting  those  containing  organic  ethers,  they 
are  not  saponifiable. 

Some  of  the  essential  oils  can  be  prepared  synthetically,  but 
most  of  them  are  obtained  by  distilling  the  plant  with  water ;  by 
extracting  it  with  solvents ;  by  pressing ;  by  maceration  in  fat ;  or 
by  erifleurage,  or  absorption  in  fat.  By  far  the  greater  number  of 
commercially  important  essential  oils  are  obtained  by  distillation 
with  water  or  steam  or  by  pressing. 

In  the  distillation  process,  the  oil-bearing  material  is  put  into  a 
still  with  a  considerable  quantity  of  water,  which  is  then  brought  to 
boiling.  The  steam  carries  the  oil  into  the  condenser  mechanically, 
where  a  mixture  of  oil  and  water  is  obtained,  which  is  usually  milky 
at  first.  On  standing,  it  separates  into  two  distinct  layers,  the  oil 


336  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

usually,  but  not  always,  on  top.  The  water  is  drawn  off,  and  re- 
turned to  the  still  with  the  new  charge;  or  the  receiver  is  so  ar- 
ranged that  the  water  returns  continuously  to  the  still  through  a 
siphon. 

When  extraction  is  employed,  alcohol,  carbon  disulphide,  ether, 
or  petroleum  naphtha,  may  be  used.  The  solvent  is  evaporated  from 
the  oil,  and  recovered. 

Some  oils,  especially  those  of  lemon  and  orange,  are  obtained  by 
the  use  of  hydraulic  or  screw  presses.  The  product  is  fragrant,  but 
rather  deeply  colored. 

Maceration  in  fat  is  employed  for  some  essences  which  are 
injured  by  high  temperatures.  The  fat  used  is  a  perfectly  pure  and 
sweet  lard,  tallow,  or  heavy  paraffine  oil  which  is  melted  in  a  water 
bath.  The  flowers  or  leaves  are  stirred  in  and  digested  until  ex- 
hausted. The  fat  takes  up  the  essential  oil  and  is  treated  with  alco- 
hol, which  extracts  part  of  the  essence.  These  alcoholic  solutions 
are  much  used  in  perfumery ;  the  fat,  still  containing  some  of  the 
essential  oil,  is  used  for  pomades  and  similar  purposes. 

Enfleurage  is  employed  for  those  very  delicate  oils  whose  odors 
are  destroyed  by  even  moderate  heat.  The  flowers  to  be  extracted 
are  laid  in  a  wooden  frame  on  the  glass  bottom  of  which  a  thin  layer 
of  perfectly  neutral  fat  is  spread.  A  number  of  frames  are  placed 
in  a  pile  and  allowed  to  stand  for  some  hours,  when  the  flowers  are 
replaced  by  fresh  ones.  This  is  repeated  until  the  fat  has  become 
strongly  charged  with  the  perfume. 

Oil  of  turpentine  or  spirits  of  turpentine  is  derived  from  conifer- 
ous trees,  especially  from  the  pine,  Pinus  palustris,  Mill.,  and  P. 
tceda,  L.,  and  from  the  Scotch  fir,  P.  sylvestris,  L.  The  trees  are 
"  boxed,"  i.e.  a  cavity  is  cut  near  the  root,  and  the  bark  channelled 
with  shallow  cuts  which  lead  down  to  the  box.  The  crude  turpen- 
tine (an  oleo-resin)  flows  from  the  cuts  and  collects  in  the  box,  from 
which  it  is  dipped  out  at  intervals.  It  forms  an  exceedingly  sticky, 
viscid  liquid  balsam  which  is  distilled  with  steam.  The  volatile  oil 
of  turpentine  (about  17  per  cent)  passes  over  with  the  steam,  while 
a  residue  of  resin  (rosin  or  colophony)  remains  in  the  still. 

.  The  oils  obtained  from  different  varieties  of  coniferce  differ  some- 
what in  their  properties.  Three  commercial  grades  are  important : 
(a)  French  turpentine  consisting  chiefly  of  a  terpene,  C10H16,  and 
called  terebenthene  or  Imvopinene,  which  has  a  laevo-rotary  action  on 
polarized  light  rays ;  (6)  American  or  English  turpentine  consisting 
of  a  terpene,  C10H16,  called  australene,  which  has  the  same  specific 
gravity,  boiling  point,  and  chemical  properties  as  terebenthene,  but 


ESSENTIAL  OILS  337 

is  dextro-rotary ;  (c)  Russian  turpentine  which  contains  the  terpene, 
sylvestrine,  and  some  of  a  pinene,  resembling  australene  but  differing 
in  its  rotary  power. 

The  oil  of  turpentine  first  distilled  is  usually  washed  with  caustic 
soda  solution  to  saponify  any  rosin  acids,  and  is  then  redistilled, 
forming  the  "  rectified  spirits  of  turpentine." 

Commercial  oil  of  turpentine  is  a  water-white,  mobile,  light  re- 
fracting liquid  of  0.640  to  0.872  sp.  gr.,  and  distilling  between 
156°  and  170°  C.  It  is  insoluble  in  water  and  in  glycerine,  but 
very  soluble  in  ether,  absolute  alcohol,  carbon  disulphide,  chloro- 
form, benzene,  fatty  oils,  and  other  essential  oils.  It  dissolves 
resins,  caoutchouc,  wax,  phosphorus,  and  sulphur.  On  exposure  to 
the  air,  it  absorbs  oxygen  and  becomes  resinous.  It  is  inflammable 
and  burns  with  much  smoke.  It  reacts  readily  with  many  chemical 
reagents,  producing  substances  used  in  medicine  and  the  arts.  Oil 
of  turpentine  or  "  turps  "  is  extensively  used  as  a  solvent  for  resins 
and  oils  in  making  varnishes  and  paints. 

According  to  Kingzett,  the  oxidation  of  turpentine  produces  cam- 
phoric peroxide,  C10H1404,  which,  when  treated  with  water,  forms 
camphoric  acid  and  hydrogen  peroxide.  By  exposing  Russian  tur- 
pentine to  a  current  of  air  in  the  presence  of  warm  water,  the  disin- 
fectant "  sanitas  "  is  made. 

Camphor,*  C10H160,  is  one  of  the  oxygenated  essential  bodies 
(probably  a  ketone)  occurring  in  many  crude  volatile  oils.  The 
commercial  article  is  obtained  from  the  wood  of  the  camphor 
laurel,  Cinnamomum  Camphora,  Nees  &  Eberm.  The  tree  is  native 
in  Japan  and  Borneo.  The  trunk  and  branches  of  the  tree  are 
roughly  distilled  with  water,  and  the  crude  camphor  purified  by 
sublimation. 

Camphor  is  a  white,  translucent,  fibrous  body  having  a  peculiar, 
penetrating  odor  and  pungent  taste.  It  melts  at  175°  C.,  and  boils 
at  204°  C.,  and  is  volatile  at  ordinary  temperatures.  Its  density  is 
0.986  to  0.996.  It  burns  with  a  very  luminous  flame,  but  emits 
much  smoke.  It  is  very  slightly  soluble  in  water,  but  dissolves 
easily  in  alcohol,  ether,  chloroform,  carbon  disulphide,  acetone,  and 
essential  oils.  It  is  largely  used  in  medicine  and  pharmacy,  and  as 
a  protective  against  the  ravages  of  insects. 

Thymol,  C10TI13  •  OH,  is  a  phenol  occurring  in  the  oil  of  thyme 

and  in  some  other  volatile  oils.     It  is  similar  to  carbolic  acid  in  its 

character,  and  it  is  obtained  by  washing  the  crude  oil  with  caustic 

soda,  the  alkaline  solution  of  thymol  being  separated  and  decom- 

*  J.  Soc.  Chem.  Ind.,  1884  (3),  353. 


338  OUTLINES  OF   INDUSTRIAL  CHEMISTRY 

posed  with  mineral  acid ;  or  the  oil  is  chilled  and  the  thymol  crys- 
tallizes and  may  be  filtered  out. 

It  is  a  colorless  crystalline  body,  having  a  specific  gravity  of 
1.028,  and  melting  at  44°  C.  It  is  very  slightly  soluble  in  water, 
but  readily  so  in  alcohol,  glacial  acetic  acid,  ether,  etc.  It  is  a  pow- 
erful antiseptic,  and  is  much  used  in  medicine  and  in  pharmacy. 

Menthol,  C10H19  •  OH,  is  an  alcohol  occurring  in  oil  of  pepper- 
mint, and  which  crystallizes  when  the  oil  is  chilled.  It  is  a  white 
solid,  very  sparingly  soluble  in  water,  but  readily  so  in  ether,  alco- 
hol, and  fixed  and  volatile  oils.  It  does  not  combine  with  caustic 
alkalies.  It  melts  at  41°  to  43°  C.  It  is  much  used  as  a  remedy  for 
neuralgic  pains  and  headache. 

The  essential  oil  of  almonds  is  produced  by  the  action  of  emulsin, 
a  nitrogenous  ferment  upon  amygdalin,  a  glucoside.  To  obtain  it, 
the  marc  of  almond  kernels  left  after  pressing  for  the  fixed  oil,  is 
distilled  with  water.  It  contains  benzaldehyde,  with  some  hydro- 
cyanic acid  and  other  nitrils.  It  is  purified  by  redistillation  over  a 
mixture  of  lime  and  ferrous  sulphate.  It  is  readily  oxidized  on  ex- 
posure to  the  air,  forming  benzoic  acid.  Artificial  almond  essence 
is  made  by  boiling  benzal  chloride  with  lead  nitrate  or  calcium  car- 
bonate and  water.  This  oil  is  used  in  making  dyes  and  as  a  flavor- 
ing extract. 

Nitrobenzene  is  used  under  the  name  "  rnirbane,"  as  a  substitute 
for  almond  essence  for  scenting  soaps. 

Oil  of  bergamot  is  prepared  from  the  fruit  of  a  species  of  orange, 
Citrus  Bergamia,  Kisso,  by  hand  pressing  or  distillation  with  water. 
It  is  a  light  green,  pleasant  smelling  oil,  containing  a  large  amount 
of  a  terpene,  citrene,  C10H16,  boiling  at  175°  to  177°  C.  It  is  chiefly 
used  in  perfumery. 

Oil  of  Cajaput,  prepared  from  the  leaves  of  Melaleuca  Leucaden- 
dron,  L.,  is  a  green  liquid  of  peculiar  odor,  distilling  at  170°  to  180°  C. 

Cedar  oil  is  obtained  by  distilling  the  wood  of  red  cedar,  Juni- 
perus  Virginiana,  L.,  with  water.  It  contains  a  mixture  of  cedrene, 
C15H24,  and  a  camphor-like  body,  C)5H260. 

Chamomile  oil,  distilled  from  Anthemis  nobilis,  L.,  consists  of 
isobutyl  and  amyl  esters  of  angelica  and  tiglic  acids. 

Cinnamon  oil  or  oil  of  cassia  is  distilled  from  the  inner  bark  of 
Cinnamomum  Zeylanicum,  Nees.  It  is  a  yellow  oil,  consisting  mainly 
of  cinnamic  aldehyde,  with  a  little  cinnamic  acid.  It  is  slightly 
heavier  than  water. 

Oil  of  cloves  is  obtained  by  distilling  cloves  (the  flower  buds  of 
Eugenia  caryophyllata,  Thunb.)  with  water.  It  is  a  mixture  of  a  ter- 


ESSENTIAL   OILS  339 

pene,  C15H24  (boiling  at  251°  C.),  and  eugenol,  C10H1202.  It  is  yellow, 
of  a  penetrating  odor  and  heavier  than  water. 

Eucalyptus  oil,  distilled  from  the  leaves  of  several  Australian 
trees,  Eucalyptus  Globulus,  Labill.,  and  others,  is  used  in  perfumery, 
in  medicine,  and  in  scenting  soaps.  It  contains  terpenes  (especially 
pinene,  C10H16),  cymene,  and  eucalyptol  or  cineol,  C10H180. 

Geranium  oil  is  distilled  from  the  leaves  of  Pelargonium  Radula, 
L'Herit.  Its  odor  resembles  that  of  rose  oil,  which  it  is  chiefly 
used  to  adulterate. 

Lavender  oil  is  distilled  from  the  flowers  of  Lavandula  vera, 
D.  C.  It  has  little  odor  when  first  prepared,  the  perfume  being 
developed  by  exposure  to  the  air.  Oil  of  spike  is  obtained  from 
L.  Spica,  Cav.  It  is  similar  to  lavender  oil  and  is  used  in  porce- 
lain painting. 

Oil  of  lemon  is  expressed  from  the  rind  of  the  fruit  of  Citrus 
Limonum,  Risso.  Poor  grades  are  made  by  distilling  the  rind.  The 
oil  contains  a  terpene  (limonene),  C10H16,  boiling  at  176°  C.  It  is 
chiefly  used  in  perfumery,  and  as  a  flavoring  essence  in  confectionery. 

Mustard  oil  is  distilled  from  the  seeds  of  Brassica  nigra,  Koch., 
after  the  fixed  oil  has  been  removed  by  pressing.  It  contains  nitro- 
gen and  sulphur,  and  its  essential  principle  is  allyl  thiocarbamide, 
C3H5N:CS.  It  is  a  pale  yellow  oil  of  1.015  to  1.025  sp.  gr., 
boiling  at  148°  C.,  and  having  a  pungent,  disagreeable  odor.  It  is  a 
powerful  irritant  and  produces  blisters  on  the  skin.  It  is  not  pres- 
ent in  dry  seeds,  but  is  formed  by  the  action  of  a  ferment,  myrosin, 
upon  a  glucoside,  potassium  myronate,  in  the  presence  of  water. 
Artificial  mustard  oil  is  prepared  by  distilling  allyl  iodide  with 
potassium  thiocyanate :  — 

C3H5I  +  KSNC  =  KI  +  C3H5 .  N  :  CS. 

Oil  of  peppermint,  obtained  by  distilling  the  herb  Mentha  piperita, 
L.,  is  a  colorless  or  greenish-yellow  liquid,  of  strong  pungent  taste 
and  odor,  having  a  specific  gravity  of  0.900  to  0.920.  It  is  a  mixt- 
ure of  menthol,  C10H19  •  OH,  with  several  terpenes.  It  is  much 
used  in  medicine  and  as  a  flavoring  essence. 

Attar  of  roses  is  obtained  by  distilling  the  flowers  of  various 
species  of  rose.  It  is  a  pale  yellowish  liquid,  somewhat  lighter 
than  water,  having  a  very  delicate,  rich  odor.  It  crystallizes  at 
ordinary  temperatures  and  deposits  an  inodorous  body  resembling 
paraffine.  The  constitution  of  the  oil  is  not  known.  Owing  to  its 
high  price,  it  is  always  adulterated  with  geranium  oil,  which  resem- 
bles it  somewhat  in  odor. 


340  OUTLINES   OF  INDUSTRIAL   CHEMISTRY 

Oil  of  rue  is  distilled  from  the  herb  Rata  graveolens,  L.  It  con- 
sists mainly  of  methyl  nonylketone,  C9H19*  CO  •  CH3. 

Oil  of  sassafras  is  distilled  from  the  root  of  Sassafras  officinale, 
Nees  &  Eberm.  It  contains  safrol,  C10H1002,  and  some  pinene,  C10HJ6. 
Safrol  melts  at  8°  C.  and  boils  at  228°  to  235°  C.  Sassafras  oil  is 
much  used  for  flavoring. 

Oil  of  thyme  or  origanum  is  derived  from  the  leaves  and  flowers 
of  Thymus  vulgaris,  L.  It  is  yellowish  red,  has  a  pungent  taste, 
and  a  specific  gravity  of  0.900  to  0.930.  It  contains  a  laevo-pinene, 
C10H16,  boiling  at  160°  C. ;  thymol,  C10H140,  and  cymene,  CioH^,  boil- 
ing at  175°  C. 

Oil  of  wormwood  is  distilled  from  the  herb  Artemisia  Absin- 
thium, L. 

Oil  of  wintergreen  is  distilled  from  the  leaves  of  Gaultheria  pro- 
cumbens,  L.  It  contains  methyl  salicylate,  C6H4  •  (OH)  •  COO  •  CH3, 
with  a  little  terpene.  It  is  a  liquid  of  pleasant  smell  and  taste, 
boiling  at  218°  C.,  and  having  a  specific  gravity  of  1.175  to  1.185 
at  15°  C.  It  rotates  the  plan  of  polarization  to  the  left.  It  is  much 
used  as  a  flavoring  essence. 

An  artificial  oil  is  made  by  heating  salicylic  acid  with  oil  of 
vitriol  and  methyl  alcohol. 

REFERENCES 

Treatise  on  the  Manufacture  of  Perfumes.     J.  H.  Snively,  New  York,  1890. 

Die  fliichtigen  Oele  des  Pflanzenreiches.     G.  Bornemann,  Weimar,  1891. 

Handbuch  der  Parfumerie-  und  Toilettenseifen-fabrication.  '  C.  Deite,  Berlin, 
1891.  (J.  Springer.) 

The  Art  of  Perfumery.    C.  H.  Piesse,  London,  1891.     5  Ed. 

Practical  Treatise  on  the  Manufacture  of  Perfumery.  W.  T.  Brannt,  Phila- 
delphia, 1892. 

Odorographia;  a  Natural  History  of  Raw  Materials  and  Drugs  used  in  the 
Perfume  Industry.  J.  Ch.  Sawer,  London,  1892,  Part  I.  1894,  Part  II. 
(Gurney  and  Jackson.) 

Perfumes  and  their  Preparation.  G.  W.  Askinson.  Trans,  by  J.  Furst,  Lon- 
don and  New  York,  1892. 

Fabrication  des  Essences,  et  des  Parfums.     P.  Durvelle,  Paris,  1893. 

Descriptive  Catalogue  of  Essential  Oils  and  Organic  Chemical  Preparations. 
F.  B.  Power,  New  York,  1894.  (Fritsche  Bros.) 

Die  Riechstoffe  u.  Ihre  Verwendung.  Dr.  St.  Mierzinski,  Weimar,  1894. 
(F.  Voigt.) 

Aether  und  Grundessenzen.     Theodor  Horatius,  Leipzig,  1895.     (Hartleben.) 

Semi- Annual  Reports.  1892 +.  Schimmel  and  Co.  (Fritsche  Bros.),  Leipzig 
and  New  York. 


RESINS  AND  GUMS  341 


RESINS  AND  GUMS 

Resins  are  oxygenated  bodies,  generally  produced  by  the  oxida- 
tion of  terpenes  or  related  hydrocarbons  in  plants  or  in  essential 
oils.  They  are  found  as  natural  or  induced  exudations  from  plants, 
often  mixed  with  the  essential  oil,  forming  oleo-resin  or  balsam,  or 
with  mucilaginous  matter,  forming  gum-resin.  True  resins  are  com- 
pact masses,  insoluble  in  water,  devoid  of  marked  taste  or  odor,  and 
usually  composed  of  substances  of  an  anhydric  or  acid  nature.  They 
are  nearly  all  soluble  in  alcohol,  ether,  benzene,  and  in  most  volatile 
oils,  and  may  usually  be  saponified  with  caustic  alkali.  When 
heated,  they  soften  below  their  melting  points,  but  cannot  be  dis- 
tilled undecomposed.  The  chief  uses  of  resins  are :  in  making  var- 
nish ;  for  soap ;  as  a  constituent  of  sealing  wax ;  in  medicine,  and  in 
sizing  paper  and  cloth. 

Common  rosin,  or  colophony,  is  a  resin  obtained  by  the  distilla- 
tion of  turpentine  oil  from  crude  turpentine  (p.  336).  Three  grades 
of  rosin  are  in  the  market,  —  "  virgin,"  yellow  dip,  and  hard.  Virgin 
rosin  is  made  from  the  first  turpentine  that  exudes  after  the  tree  is 
"boxed."  It  is  of  a  very  light  yellow  or  amber  color.  The  greater 
part  of  the  crude  turpentine  furnishes  yellow  dip.  The  hard  is 
made  from  the  scrapings  from  the  tree  after  the  turpentine  has  be- 
come too  thick  to  run  into  the  box ;  it  is  very  dark,  being  nearly 
black. 

"  White  rosin "  contains  some  water,  which  renders  it  opaque ; 
but  as  soon  as  the  water  evaporates,  the  whiteness  disappears. 

Rosin  is  very  brittle,  melts  at  100°  to  140°  C.,  and  has  a  specific 
gravity  of  about  1.08.  It  contains  a  large  amount  of  abietic  anhy- 
dride, CuH6204,  which  is  readily  converted  into  abietic  acid,  C^H^Og. 
Rosin  is  converted  by  alkalies  into  "  rosin  soap  "  (p.  323),  which  is 
deliquescent  and  very  soluble  in  water.  Rosin  is  used  as  a  constitu- 
ent of  laundry  soaps ;  as  an  addition  to  cheap  varnishes ;  and  as  a 
flux  in  soldering  and  brazing  rnetals ;  in  pharmacy ;  in  ship  calking ; 
and  as  an  adulterant  of  fats,  waxes,  and  mineral  oils. 

Rosin  must  not  be  confounded  with  wood-tar,  or  pitch,  obtained 
by  the  destructive  distillation  of  wood. 

Rosin  may  be  distilled  in  vacua,  or  by  the  aid  of  superheated 
steam,  with  very  little  decomposition ;  but  when  heated  in  a  retort, 
it  yields  decomposition  products  consisting  of  gases,  liquids,  and 
pitch.  The  liquid  distillate  is  composed  mainly  of  "  rosin  spirit,"  *  a 

*  Renard.    J.  Chem.  Soc.,  46,  843. 


342  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

very  complex  body,  boiling  below  360°  C.,  resembling  oil  of  turpen- 
tine, for  which  it  is  sometimes  substituted,  and  "  rosin  oil,"  *  a  heav- 
ier liquid,  boiling  above  360°  C. 

The  rosin  oil  is  purified  by  treatment  with  a  little  sulphuric  acid, 
followed  by  lime  water,  and  then  redistilled,  sometimes  with  caustic 
soda  in  the  still.  It  has  a  specific  gravity  of  0.980  to  1.100 ;  is  water 
white  to  brown  in  color,  and  is  very  slightly  soluble  in  alcohol,  but 
easily  dissolved  in  fatty  oils,  ether,  chloroform,  etc.  It  is  nearly 
odorless,  and  has  a  strong,  peculiar  taste.  It  is  not  subject  to  true 
saponification,  although  when  treated  with  milk  of  lime,  a  combina- 
tion between  the  terpenes  of  the  oil  and  the  calcium  hydroxide  takes 
place,  forming  a  solid  mass.  This  is  stirred  up  with  more  rosin  oil, 
to  form  a  soft  mixture  of  about  the  proportions,  13  C10H16  •  Ca  (OH)2, 
which  is  the  commercial  "rosin  grease,"  used  as  a  lubricant  on  iron 
bearings.  Rosin  oil  is  largely  used  in  making  such  lubricants,  and 
as  an  adulterant  for  olive  and  boiled  linseed  oils. 

Burgundy  pitch  is  a  resin  resembling  common  rosin,  but  obtained 
from  the  Norway  spruce,  Picea  excelsa,  Link.  The  trees  are  scari- 
fied, and  the  resin  allowed  to  harden,  when  it  is  collected  and  treated 
with  boiling  water,  to  remove  the  volatile  oils.  Its  chief  constituent 
is  abietic  anhydride.  When  stirred  up  with  fats  and  water,  melted 
rosin  forms  a  mass  resembling  Burgundy  pitch,  in  its  opacity  and 
other  properties. 

Mastic  and  Sandarac  are  somewhat  similar  resins,  obtained  from 
evergreen  shrubs  which  grow  along  the  shores  of  the  Mediterranean 
Sea,  especially  on  the  island  of  Chios,  and  in  northern  Africa.  The 
former,  derived  from  Pistada  Lentiscus,  L.,  occurs  in  commerce  as 
small  translucent  grains,  or  "tears,"  which  soften  when  masticated 
and  have  a  slightly  bitter,  aromatic  taste.  It  is  soluble  in  acetone 
alcohol,  and  turpentine  oil,  and  is  used  in  varnish  making  and  in 
pharmacy. 

Sandarac,  also  called  "gum  juniper,"  is  obtained  from  CaUitris 
quadrivalvis,  Vent.,  an  evergreen  growing  in  northern  Africa.  It  is 
used  in  varnishes. 

Amber  is  a  fossil  resin  found  along  the  coast  of  the  Baltic  Sea,  in 
Germany.  It  is  the  hardest  and  heaviest  of  all  resins,  is  capable  of 
taking  a  high  polish,  and  is  insoluble  in  most  of  the  ordinary  sol- 
vents. Its  color  varies  from  very  light  yellow  to  deep  brownish  red. 
It  often  contains  perfect  specimens  of  fossil  insects.  When  heated 
above  its  melting  point,  it  is  partly  decomposed,  and  then  becomes 
soluble  in  alcohol  and  in  oil  of  turpentine. 

*  Kenard.    J.  Chem.  Soc.,  24,  304, 1175. 


RESINS  AND  GUMS  343 

Transparent  pieces  of  amber  are  much  prized  for  jewelry,  fancy 
articles,  mouth-pieces  for  pipes  and  cigar  holders,  and  for  other  orna- 
mental purposes.  It  is  also  used  in  preparing  a  fine  transparent 
varnish  for  use  on  negatives  in  photography. 

When  subjected  to  destructive  distillation,  amber  yields  a  gas,  an 
organic  acid  (succinic  acid),  and  an  oil  called  "oil  of  amber."  This 
oil  and  the  acid  are  used  somewhat  in  pharmacy.  By  treating  oil  of 
amber  with  fuming  nitric  acid,  a  substance  resembling  musk  in  odor, 
and  other  properties  is  obtained.  But  the  artificial  musk*  of  com- 
merce is  now  made  from  butyl  toluene,  by  the  action  of  nitric  and 
sulphuric  acids. 

Copal  is  a  very  valuable  resin.  Soft  copal,  soluble  in  ether,  is 
obtained  from  living  trees  in  Java,  Sumatra,  the  Philippine  Islands, 
and  New  Zealand.  The  better  quality,  hard  copal,  is  a  fossil  gum, 
found  in  irregular  lumps,  buried  in  the  earth,  in  the  East  Indies, 
Madagascar,  West  Africa,  and  South  America,  the  last  variety  being 
called  gum  animi.  Hard  copal  varies  in  color  from  pale  yellow  to 
brown.  Its  specific  gravity  is  usually  1.059  to  1.072.  It  has  a  higher 
melting  point  than  soft  copal,  and  is  insoluble  in  ether  or  volatile 
oils.  But  by  heating  above  its  melting  point,  a  partial  decomposition 
takes  place,  and  the  resin  is  rendered  more  soluble  in  these  solvents. 

Hard  copal  is  the  hardest  of  all  resins,  except  amber,  and  is  most 
valuable  for  varnish  making.  For  this  it  must  first  be  melted,  or 
"  run,"  and  while  in  the  liquid  state,  hot  oil  of  turpentine  is  slowly 
added  and  mixed  with  it. 

Dammar  is  obtained  from  a  coniferous  tree,  Agathis  loranthifolia, 
Salisb.,  in  the  Moluccas.  The  resin  exudes  from  the  tree  in  drops, 
and  is  collected  after  it  dries.  It  is  soluble  in  essential  and  in  fixed 
oils,  in  crude  benzene,  and  partially  so  in  alcohol  and  ether.  It  is 
very  light  colored,  and  makes  a  very  transparent  varnish. 

Kauri,  or  Australian  dammar,  is  obtained  from  a  New  Zealand 
tree,  Agathis  australis,  Stend.  Much  of  the  kauri  of  trade  is  a  fossil 
resin,  and  is  somewhat  darker  colored  than  the  true  dammar  and 
copal.  It  is  extensively  used  for  varnish  making,  being  cheaper 
than  copal. 

Dragon's  blood  is  a  deep  crimson  red  resin,  which  exudes  from 
the  fruit  of  a  palm  tree,  Dcemonorops  Draco,  Blume.,  indigenous  in 
the  East  Indies.  It  is  collected  by  the  natives  and  made  into  irregu- 
lar lumps,  or  cast  into  long  sticks  in  moulds  made  by  rolling  palm 
leaves  into  cylinders  and  closing  one  end.  It  is  freely  soluble  in 
nearly  all  of  the  ordinary  solvents,  except  petroleum  ether,  oil  of 
*  Bauer.  Berichte  der  deutschen  chemischen  Gesellschaft,  24,  2832. 


344  OUTLINES  OF  INDUSTRIAL   CHEMISTRY 

turpentine,  and  ether.  It  is  slightly  soluble  in  the  two  latter.  It  is 
used  in  pharmacy,  and  in  certain  colored  varnishes. 

Guaiacum  is  a  resin  derived  from  certain  West  Indian  trees, 
especially  Guaiacum  sanctum,  L.,  and  G.  officinale,  L.  It  exudes  from 
the  trees  through  incisions,  and  forms  "  tears  "  or  lumps  which  are 
sent  to  market.  It  is  soluble  in  ether,  alcohol,  chloroform,  acetone, 
and  caustic  soda.  Its  alcoholic  solution  is  employed  as  a  reagent 
for  oxidizing  substances,  with  which  it  shows  a  blue  color,  which  is 
destroyed  by  reducing  agents,  but  reappears  when  again  oxidized. 
Hydrogen  peroxide,  however,  does  not  change  the  color  to  blue  unless 
in  the  presence  of  blood.  Hence  guaiacum  in  alcohol,  with  hydrogen 
peroxide,  is  used  as  a  reagent  for  detecting  blood  stains.  Guaiacum 
is  also  used  in  medicine  in  treating  rheumatism  and  gout. 

Lac  is  a  resin  produced  by  the  bite  or  sting  of  certain  insects, 
Coccus  lacca,  Kerr,  on  the  small  twigs  of  several  species  of  East 
Indian  trees,  of  which  Picas  Indica,  L.,  and  F.  religiosa,  L.,  are  the 
chief.  The  resin  appears  to  be  formed  from  the  plant  sap  by  the 
female  insect,  from  whose  body  it  exudes,  ultimately  burying  the 
insect  and  her  eggs,  and  forming  a  thick  excrescence  on  the  twigs. 
It  is  collected,  together  with  the  twigs  which  it  envelopes,  and  is 
brought  into  commerce  as  "stick  lac."  The  insect  also  secretes  a 
brilliant  red  dye  which  is  extracted  by  macerating  the  crude  lac  in 
warm  water.  The  aqueous  solution  is  evaporated  to  dryness,  and  the 
residue  sold  as  lac-dye.  After  the  dye  is  extracted,  the  resin  is 
known  as  "seed  lac."  This  is  refined  by  carefully  melting  and 
straining  through  muslin  bags  to  remove  foreign  matter.  The  melted 
lac  is  then  poured  in  thin  films  over  cold  porcelain,  copper,  or  wood 
cylinders,  or  plates,  and  allowed  to  cool,  when  it  hardens  and  scales 
off  in  thin  flakes,  and  is  called  "  shellac."  Or  it  is  poured  into  moulds 
to  form  "  button,"  or  "  garnet  lac."  The  shellac  is  the  better  quality, 
and  is  of  a  pale  orange,  or  red  color,  and  is  nearly  transparent.  It  is 
used  for  spirit  varnish. 

Lac  is  partially  soluble  in  strong  alcohol,  forming  a  turbid,  gummy 
liquid  much  used  as  a  varnish  and  wood  filler.  It  is  partly  soluble 
in  ether,  chloroform,  and  turpentine,  but  is  completely  dissolved  by 
caustic  alkalies  and  borax  solutions.  Such  solutions  are  used  as 
water  varnishes.  Lac  is  also  used  as  the  basis  of  the  better  grades 
of  sealing  wax. 

Bleached  shellac  is  made  by  passing  a  stream  of  chlorine  gas  into 
an  alkaline  solution  of  lac ;  the  precipitated  lac  is  melted  under  water 
and  "pulled"  to  make  it  white  and  fibrous.  It  is  used  for  white 
varnishes. 


RESINS   AND   GUMS  345 

Elemi  is  a  resin  obtained  from  certain  trees,  Canarium  commune, 
L.,  in  the  Philippine  Islands,  Canarium  Mauritianum,  Blnme.,  in 
Mauritius,  Amyris  elemifera  in  Mexico,  and  from  several  varieties  of 
Idea  in  Brazil.  The  resin  varies  from  white  to  gray  in  color,  and  is 
soft  and  tough.  It  softens  at  75°  C.,  and  melts  completely  at  120°  C. 
It  is  soluble  in  alcohol  and  other  solvents,  and  is  used  chiefly  to  give 
toughness  to  varnishes  made  from  harder  resins. 

VARNISHES 

The  resins  are  chiefly  important  as  furnishing  the  material  for 
varnish  making.  A  varnish  is  a  solution  of  a  resin,  or  of  a  drying 
oil,  which,  when  exposed  to  the  air,  becomes  hard  and  impervious  to 
air  and  moisture,  through  evaporation  of  the  solvent  or  oxidation  of 
the  oil.  Three  classes  of  varnishes  are  important :  (1)  Spirit  var- 
nishes, consisting  of  resin  dissolved  in  alcohol,  petroleum  spirit, 
acetone,  or  in  any  other  volatile  solvent ;  (2)  turpentine  varnishes, 
in  which  the  resin  is  dissolved  in  oil  of  turpentine ;  and  (3)  linseed 
oil  varnishes,  which  may  consist  of  linseed  oil  alone,  or  with  the 
addition  of  resin  and  turpentine  oil. 

Spirit  varnish  dries  rapidly,  leaving  the  resin  as  a  thin  and 
brilliant  film  on  the  surface  to  which  it  is  applied.  This  film  is  very 
brittle,  and  liable  to  crack  and  scale  off.  The  addition  of  turpentine 
overcomes  this  difficulty  to  some  extent.  Spirit  varnishes  are  very 
often  colored  with  dyes  soluble  in  alcohol,  or  with  dragon's  blood, 
gamboge,  or  cochineal.  The  most  important  spirit  varnishes  are 
made  with  shellac,  though  mastic,  sandarac,  and  dammar  are  used. 

Turpentine  varnish  is  tough  and  flexible,  but  much  slower  in 
drying  than  the  spirit  varnishes.  The  resin  is  simply  dissolved  in 
the  hot  oil,  and  after  cooling  is  ready  for  use. 

Linseed  oil  varnishes  are  the  most  important.  If  well  boiled  oil 
(p.  308)  is  applied  to  a  surface  it  dries  to  a  hard  film,  but  without 
much  brilliancy  of  surface.  By  dissolving  a  resin  in  the  boiled  oil 
and  thinning  to  the  proper  consistency  with  turpentine,  a  varnish  is 
obtained  which  dries  with  a  very  hard,  glossy  surface,  impervious  to 
air  and  moisture.  The  resins  used  are  mainly  amber,  copal,  anime, 
kauri,  and  dammar,  for  transparent  varnish.  The  hard  resins  are 
not  directly  soluble  in  the  oil,  but  must  first  be  partly  decomposed, 
or  "  run,"  by  heating  above  their  melting  points.  There  is  consider- 
able evolution  of  irritating  gases  during  this  fusion,  and  an  oily 
distillate  is  often  collected.  The  residue  in  the  pot  is  then  soluble 
in  the  hot  boiled  oil,  which  is  run  direct  from  the  boiling  kettle  into 


846  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

the  resin  melting  kettle.  After  thorough,  stirring  the  mixture  is 
usually  heated  some  time  longer  to  secure  homogeneous  solution.  It 
is  then  cooled  to  about  130°  or  140°  C.,  and  thinned  to  the  desired 
consistency  with  oil  of  turpentine.  The  varnish  is  allowed  to  stand 
in  storage  tanks  for  several  months,  or  even  for  a  year  or  two,  until 
thoroughly  clarified. 

The  boiling  of  the  oil  and  of  the  varnish  involves  considerable  risk 
from  fire.  The  oil  froths  very  much,  and  the  vapors  given  off  are 
inflammable,  hence  it  is  usually  the  custom  to  build  the  furnace  with 
the  fire-door  opening  through  a  partition  into  another  room.  The 
vapors  should  be  led  into  a  flue  having  a  good  draught. 

OLEO-RESINS 

Oleo-resins  are  mixtures  of  the  resin  and  the  essential  oil  of  the 
plant  from  which  they  exude.  Among  them  is  a  group  of  substances 
which  have  peculiar  odor  and  pungent  taste,  and  which  are  called 
balsams.  They  are  the  exudations  from  tropical  trees  belonging  to 
the  genera  Myroxylon  and  Styrax.  The  most  important  are  Benzoin, 
Peru,  Tolu,  and  Storax  balsams.  They  contain  free  benzoic  or  cin- 
namic  acids,  or  compounds  of  them,  to  which  their  peculiar  properties 
are  due.  The  balsams  are  chiefly  used  in  medicine  and  pharmacy, 
and  for  incense  and  perfumes. 

The  so-called  Canada  balsam  is  an  oleo-resin  containing  turpen- 
tine, and  is  not  a  true  balsam. 

CAOUTCHOUC  OR  INDIA  RUBBER 

Belated  to  the  resins  and  essential  oils  is  caoutchouc  or  India 
rubber.  This  is  suspended  in  minute  globules  in  the  juice  or  latex 
of  certain  plants  belonging  to  the  orders  Euphorbiacece,  Apocynacem, 
and  Artocarpacece,  native  in  nearly  all  tropical  countries.  There 
are  some  60  species  grouped  in  the  5  genera,  Havea,  Maniliot,  Vahea, 
Landolphia,  and  Castilloa.  The  finest  grades  come  from  South  Amer- 
ica (Para),  and  Madagascar.  In  Brazil  the  trees  are  from  12  to  15 
years  old  when  tapped,  and  yield  about  10  pounds  of  milky  juice,  or 
over  3  pounds  of  gum  daily.  Medium  and  low  grades  are  obtained 
from  Central  America,  East  India,  Java,  Borneo,  and  the  west  coast 
of  Africa.  The  plants  in  Africa  are  generally  vines ;  the  bark  is 
partly  stripped  off,  and  the  juice  coagulates  on  the  vine  by  the 
evaporation  of  its  very  volatile  constituents. 

The  juice,  which  is  quite  distinct  from  the  sap  of  the  rubber 
plant,  and  some  of  whose  constituents  are  probably  waste  products 
as  far  as  the  vital  processes  of  the  plant  are  concerned,  is  collected 


RESINS  AND   GUMS  347 

in  July,  August,  October,  and  November.  It  is  coagulated  by  heating 
and  exposing  in  thin  layers  to  the  smoke  of  burning  palm  nuts,  as  in 
Brazil ;  or  it  is  boiled  with  water ;  or  dilute  acid,  salt  water,  wood- 
ash  lye,  or  alum  is  added,  in  which  case  the  crude  rubber  is  usually 
wet  and  porous. 

Caoutchouc  has  the  composition  (C10H16)n,  and  is  therefore  a 
polymer  of  terpene.  Commercial  caoutchouc  appears  to  contain 
two  modifications,  one  soft  and  viscous,  and  the  other  hard  and 
fibrous.  These  have  the  same  properties  in  general,  but  differ 
in  solubility  in  cold  benzene  or  naphtha;  the  hard  variety  swells 
and  softens,  while  the  viscous  caoutchouc  dissolves  to  form  a  true 
solution.  Fresh  samples  are  nearly  white,  but  darken  on  exposure. 
Commercial  grades  are  nearly  black,  owing  to  discoloration  by 
smoke  and  exposure  to  the  air,  and  often  have  a  very  foul  odor 
due  to  fermentation.  When  soaked,  the  crude  gum  absorbs  from 
10  to  25  per  cent  of  water.  It  is  sticky,  and  freshly  cut  surfaces 
unite  very  firmly.  Dilute  acids  and  alkalies  have  no  action  on  it, 
but  strong  acids  and  free  chlorine  or  bromine  destroy  it.  Oils  and 
grease  also  cause  it  to  become  hard  and  brittle  after  a  time.  It  is 
soft  and  elastic  at  ordinary  temperatures,  and  if  heated  becomes 
very  sticky  and  loses  its  elasticity  at  about  120°  C.,  and  melts  at 
150°  C.  It  is  soluble  in  carbon  disulphide  and  chloroform  and 
partially  so  in  ether,  oil  of  turpentine,  benzene,  and  naphtha.  Its 
specific  gravity  is  0.915. 

The  crude  gum  contains  much  dirt,  sand,  gravel,  bark,  etc., 
which  is  removed  by  a  washing  process.  It  is  boiled  in  water 
until  softened,  and  is  then  ground  between  corrugated  rolls,  which 
flatten  the  lumps  into  thin  sheets  while  a  stream  of  water  plays 
over  the  mass,  washing  away  the  impurities.  Good  Para  rubber 
loses  about  15  per  cent  of  its  weight  during  this  washing,  while  low 
grades  shrink  from  30  to  40  per  cent.  Following  the  washing,  the 
rubber  is  very  thoroughly  dried,  hanging  for  several  weeks  in  well 
ventilated  lofts  heated  to  90°  F.  This  leaves  it  very  pure.  But 
for  most  manufacturing  purposes,  a  pure  gum  is  neither  necessary 
nor  desirable,  and  in  order  to  impart  to  it  certain  properties,  it  is 
mixed  or  "  compounded  "  with  various  materials.  This  is  done  in 
a  "  mixing  mill,"  which  consists  of  a  pair  of  heavy,  smooth,  hollow, 
iron  rollers,  one  of  which  is  heated  by  steam  to  about  80°  C.  The 
materials  added  are  vulcanizing  agents  such  as  sulphur,  metallic 
sulphides  and  oxides,  coloring  pigments,  fillers,  or  inert  "make 
weights,"  such  as  whiting,  barytes,  plaster  of  Paris,  etc.,  rubber 
substitutes,  or  cheap  gums.  These  are  thoroughly  ground  with  the 


348  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

gum  to  produce  a  homogeneous  mass,  which  can  then  be  fashioned 
into  any  desired  form  and  finally  vulcanized. 

The  clean  surfaces  of  unvulcanized  rubber  will  unite  if  brought 
in  contact  with  each  other.  It  is  on  this  property  that  the  manu- 
facture of  soft  rubber  goods  chiefly  depends.  In  order  to  prevent 
accidental  adhesion,  fresh  surfaces  are  dusted  with  talc,  starch,  or 
flour,  or  pieces  of  plain  cotton  sheeting  are  interposed. 

Vulcanization  or  curing  is  a  chemical  change,  whose  nature 
is  not  understood,  which  is  produced  in  the  rubber  by  heating  it 
with  sulphur,  metallic  sulphides  or  oxides.  It  can  be  carried  011 
by  dry  heat  at  125°  C.,  if  some  metallic  oxide,  such  as  litharge  or 
zinc  oxide  is  present  in  the  compound.  The  goods  are  placed  in  a 
closed  chamber  heated  by  steam  ;  the  latter,  however,  does  not  come 
into  contact  with  the  rubber,  as  it  does  when  curing  with  wet 
heat.  Metallic  oxides  are  much  used  for  this  form  of  vulcanizing. 

A  cold  process  of  vulcanizing  was  discovered  by  Alexander 
Parkes.  This  consists  in  soaking  the  rubber  article  in  a  solution 
of  sulphur  chloride  in  carbon  disulphide.  It  can  only  be  used  for 
small  articles  having  thin  layers  of  caoutchouc,  since  the  action  of 
the  solution  is  merely  superficial. 

For  soft  rubber  goods,  about  10  per  cent  of  sulphur  is  added  in 
the  compounding  mill,  but  only  a  part  of  this  sulphur  is  chemically 
combined  in  curing,  the  remainder  being  mechanically  mixed  with 
the  product. 

Vulcanizing  destroys  the  adhesive  property  of  rubber  and  ren- 
ders it  more  elastic,*  less  soluble,  and  less  susceptible  to  temperature 
changes,  —  it  neither  becomes  sticky  when  moderately  heated,  nor 
brittle  when  cold.  If  antimony  sulphide,  Sb2S5,  is  used  when  vul- 
canizing, the  color  of  the  product  is  red,  owing  to  the  formation  of 
the  trisulphide,  Sb2S3,  the  remainder  of  the  sulphur  combining  with 
the  rubber. 

Rubber  substitutes  are  extensively  used  in  the  so-called  mechanical 
goods,  such  as  bicycle  pedals,  door-mats,  solid  cushions,  and  springs. 
The  best  of  these  is  balata,  obtained  from  the  juice  of  Mimusops 
KauJci,  L.,  a  tree  native  in  Guiana.  This  is  an  intermediate  sub- 
stance between  gutta-percha  and  caoutchouc. 

By  mixing  powdered  sulphur  with  raw  linseed  oil  f  and  heating 
in  a  vulcanizer,  a  substance  resembling  rubber  is  obtained.  Or  by 
treating  the  oil  with  sulphur  chloride,  a  gummy  mass  of  light  color 

*  When  unvulcanized  rubber  is  stretched,  it  regains  its  original  form  only  very 
slowly. 

t  Rape  seed  and  castor  oils  are  much  used  abroad  for  these  rubber  substitutes. 


RESINS   AND  GUMS  349 

is  produced.  These  "  sulphurized  oils  "  are  largely  mixed  with  low 
grade  rubber  and  with  coal-tar  or  resins,  for  cheap  goods.  Some- 
times they  are  used  without  the  addition  of  any  rubber  whatever. 

"Reclaimed"  or  " devulcanized "  rubber  is  made  by  grinding  old 
rubber  stock  and  scraps  to  a  powder  and  sifting  out  the  cloth  or 
other  fibre  present;  then  the  powder  is  agglomerated  by  heating 
with  steam  at  100  pounds  pressure,  and  then  dried.  Sometimes  the 
fibres  are  destroyed  by  boiling  with  dilute  sulphuric  acid;  after 
washing,  the  mass  is  steamed  as  above.  Or  the  old  rubber  is 
boiled  in  an  8  per  cent  caustic  soda  solution,  and,  after  washing 
and  drying,  is  dissolved  in  carbon  disulphide  or  benzene.  The 
solvent  is  distilled  off  to  obtain  the  rubber. 

Reclaimed  rubber  has  very  little  strength,  and  is  usually  incor- 
porated with  fresh  gum. 

Vulcanized  rubber  deteriorates  by  keeping,  and  ultimately  be- 
comes hard  and  brittle.  This  apparently  occurs  through  oxidation, 
and  is  largely  influenced  by  the  nature  of  the  compound,  oxidizing 
substances  such  as  lampblack  being  especially  liable  to  spoil  the 
rubber. 

Rubber  cement  is  made  by  dissolving  a  pure  rubber  in  cold 
naphtha.  A  little  powdered  chalk  is  usually  added. 

The  uses  of  rubber  are  exceedingly  numerous,  but  the  largest 
quantities  are  used  for  overshoes,  boots,  rubber  clothing,  bicycle 
tires,  and  hose.  It  may  be  moulded,  as  for  boot  heels,  solid  rubber 
hose,  etc.,  or  made  into  rubber  fabric.  This  latter  is  done  by  spread- 
ing a  thin  layer  of  the  unvulcanized  rubber  compound  on  a  backing 
of  cotton  or  woollen  cloth.  The  rubber  may  be  calendered  in  such  a 
way  that  it  penetrates  between  the  fibres  ("friction  coating"),  or  it 
may  be  simply  applied  to  the  surface  of  the  cloth  ("even  motion 
coating").  Rubber  shoes  and  clothing,  and  other  fabric  articles  are 
entirely  put  together  before  vulcanizing,  the  seams  being  joined  by 
rolling  the  edges  into  contact,  when  they  adhere.  Such  goods  are 
usually  vulcanized  by  heating  at  260°  E.  for  about  six  hours. 

Hard  rubber,  vulcanite,  or  ebonite  is  usually  made  from  the 
cheaper  grades  of  rubber,  especially  that  from  Borneo  and  Java, 
and  contains  a  large  amount  of  filling  material.  From  25  to  50  per 
cent  of  sulphur  is  added,  and  the  mass  heated  to  140°  to  150°  C.,  in 
vulcanizing.  It  is  often  shaped  in  the  form  desired  after  it  has 
been  vulcanized. 


350  OUTLINES   OF  INDUSTRIAL   CHEMISTRY 


GUTTA-PERCHA 

Gutta-percha*  is  obtained  from  the  juice  of  Dichopsis  Gtitta, 
Benth.  &  Hook.,  a  tree  native  in  the  East  Indies.  The  tree  is 
tapped  in  much  the  same  way  as  for  caoutchouc.  The  crude 
material  is  purified  by  grinding  in  hot  water,  by  which  the  chips, 
bark,  sand,  etc.,  are  removed.  The  plastic  mass  is  then  rolled  into 
sheets  or  formed  into  threads  and  rolled  into  balls  and  pressed. 
In  composition  it  is  a  terpene  (C10H16)U,  but  it  also  contains  some 
oxygenated  resinous  bodies.  Its  texture  is  fibrous,  its  color  varies 
from  white  to  brown,  and  when  free  from  air  its  specific  gravity  is 
slightly  greater  than  1.000.  It  is  tough  and  inelastic  when  cold, 
but  becomes  very  plastic  at  50°  C.,  and  melts  at  120°  C.  It  is  solu- 
ble in  carbon  disulphide,  chloroform,  and  warm  benzene.  Alkalies 
and  dilute  acids  have  no  action  on  it,  but  strong  nitric  and  sulphuric 
acids  destroy  it.  By  vulcanizing  with  sulphur,  it  is  rendered  harder 
and  less  plastic  when  heated.  It  is  very  easily  oxidized  in  the  air 
and  becomes  brittle.  It  is  a  very  poor  conductor  of  electricity  and 
is  better  than  rubber  for  insulating  purposes,  for  which  it  finds  its 
chief  use. 

GUM   RESINS 

Gum  resins  are  exudations  from  plants ;  they  are  the  inspissated 
juice,  and  contain  both  gum  and  resin.  They  form  emulsions  with 
water,  a  portion  of  the  gum  dissolving. 

Ammoniacum  is  derived  from  a  Persian  plant,  Dorema  Ammonia- 
cum,  Don.  It  forms  drops,  yellow  on  the  surface  and  milky  within. 
It  is  partly  soluble  in  water,  and  has  a  peculiar  odor  and  bitter 
taste.  It  is  employed  in  medicine. 

Asafoetida  is  obtained  from  the  roots  of  two  plants,  Ferula  Nar- 
thex,  Boiss.,  and-.F.  foetida,  Eegel,  native  in  Thibet  and  Turkistan. 
It  forms  tears  and  nodules,  frequently  contaminated  with  earthy 
impurities.  It  has  a  powerful  garlic  odor  and  bitter  taste.  It  is 
mainly  used  in  medicine  as  a  stimulant. 

Euphorbium  is  derived  from  a  species  of  cactus,  Euphorbia  resini- 
fera,  Berg.,  native  in  Morocco.  It  has  a  very  pungent  taste,  an  aro- 
matic odor,  and  the  powdered  gum  irritates  the  throat  and  nose. 
It  is  a  violent  emetic  and  purgative,  and  is  chiefly  used  in  veteri- 
nary medicine. 

Galbanum  is  obtained  from  Persian  plants,  probably  Ferula  g^l- 
baniflua,  Boiss.  &  Buhse.  It  forms  tears,  or  irregular  lumps,  of 

*  J.  Soc.  Chem.  Ind.,  1897,  815. 


RESINS   AND   GUMS  351 

brownish  yellow  color,  aromatic  odor,  and  bitter  taste.  The  several 
varieties  found  in  commerce  are  used  in  medicine,  and  as  con- 
stituents of  incense. 

Gamboge  (p.  208)  is  an  orange-red  substance,  derived  from  a  tree, 
Garcinia  Hanburyi,  Hook.,  or  G.  Morella,  Desr.,  native  in  Cochin 
China,  and  Siam.  It  is  soluble  in  alcohol,  has  an  acrid  taste,  and  is 
a  powerful  purgative.  Its  chief  uses  are  in  medicine,  and  as  a 
pigment. 

Myrrh  is  obtained  from  a  shrub,  Commiphora  Myrrha,  EngL, 
growing  on  the  coast  of  Arabia.  It  comes  in  commerce  as  red- 
brown,  dusty  lumps,  breaking  with  an  oily  appearing  fracture.  It 
has  a  fragrant  odor  and  bitter  taste,  and  emulsifies  with  water. 
It  is  used  as  a  tonic  in  medicine,  and  in  preparing  incense. 

Olibanum  or  frankincense  is  derived  from  several  species  of  Bos- 
wellia,  the  trees  being  native  in  Africa  and  Arabia.  It  forms  tears 
of  a  yellow  brown  color  and  milky  appearance.  It  has  a  slight 
turpentine-like  taste,  and  an  aromatic  odor.  It  forms  an  emulsion 
with  water,  and  was  formerly  much  used  in  medicine.  It  is  now 
chiefly  employed  in  preparing  incense. 

GUMS 

Gums  are  amorphous  bodies  of  complex  constitution,  nearly  all  of 
vegetable  origin,  and  soluble  in,  or,  at  least,  gelatinizing  with  water, 
but  insoluble  in  alcohol.  When  boiled  with  dilute  acid  they  yield 
sugars,  and  when  oxidized  are  converted  into  oxalic  or  mucic  acids. 

Acacia,  Gum  Arabic,  or  Gum  Senegal,  is  derived  from  numerous 
plants  of  the  Acacia  family,  mostly  native  in  Africa.  It  forms 
lumps  of  various  sizes,  ranging  in  color  from  transparent  white  to 
red-brown.  Its  chief  constituent  is  arabic  acid,  or  arabin,  C^H^On, 
as  calcium  salt.  It  dissolves  in  cold  or  hot  water  with  equal  readi- 
ness, and  is  much  used  in  pharmacy  in  preparing  emulsions.  Low 
grades  are  used  for  mucilage,  in  calico  printing,  in  thickening  ink 
and  water  colors,  and  as  stiffening  in  cloth. 

Tragacanth  is  an  exudation  from  Astragalus  gummtfer,  Labill., 
growing  in  the  Levant.  It  forms  dull  white,  translucent  plates, 
which  swell  in  water  and  partly  dissolve,  forming  a  thick  mucilage. 
Its  uses  are  similar  to  those  of  gum  Arabic. 

Agar-agar  or  Bengal  isinglass  is  a  dried  seaweed,  Gracilaria  liche- 
noides  and  Eucheuma  spinosum,  collected  in  China.  It  forms  a  jelly 
with  water. 

Iceland  moss,  Cetraria  islandica,  yields   a  jelly  containing  two 


352  OUTLINES  OF  INDUSTRIAL   CHEMISTRY 

gums,  liehenine,  C6H1005,  and  isolichenine.     The  former  is  not  col- 
ored blue  by  iodine,  while  the  latter  is. 

Irish  moss,  Chondrus  crispus,  yields  a  soluble  gum,  which  is  not 
colored  blue  by  iodine. 

REFERENCES 

Report  on  the  Gums,  Resins,  Oleo-resins,  and  Resinous  Products  of  India.     M. 

C.  Cooke,  London,  1874. 
Manufacture  of  India  Rubber  and  Gutta-percha.    Cantor  Lectures  Soc.  of  Arts. 

Thos.  Bolas,  London,  1880. 
Varnishes,  Lacquers,  Siccatives,  and  Sealing  Waxes.     E.  Andres.     Translated 

by  Wm.  T.  Brannt,  Philadelphia,  1882.     (H.  C.  Baird  &  Son.) 
Practical  Treatise  on  Caoutchouc  and  Gutta-percha.     R.  Hoffer.     Translated 

by  Wm.  Brannt,  Philadelphia,  1883.     (Baird  &  Co.) 
Die  Fabrikation  der  Kautschuk-  und  Gutta-perchawaaren.     C.    Heinzerling, 

Braunschweig,  1883.     (Vieweg.) 
Oils  and  Varnishes.     James  Cameron,  Philadelphia,  1886.     (Blakiston,  Son 

&  Co.) 
Practical  Treatise  on  the  Raw  Material  and  Manufacture  of  Rubber.     G.  N. 

Nesienson,  New  York,  1890. 

Der  Fabrikation  der  Lacke,  und  Firnisse.     Paul  Lohmann,  Berlin,  1890. 
Fossil  Resins.     C.  Lawn  and  H.  Booth,  New  York,  1891. 
Die  Fabrikation  der  Lacke  Firnisse,  u.    s.  w.     E.  Andres.     4te  Auf.     Wien, 

1891.  (Hartleben.) 

India  Rubber.     Special  Consular  Reports,  Washington,  1892.     (Government 

Printing  Office.) 

Notes  on  Varnish  and  Fossil  Resins.    R.  I.  Clark,  London,  1892  (?). 
Le  Caoutchouc  et  la  Gutta  Percha.    E.  Chapel,  Paris,  1892. 
Painters'  Colours,  Oils,  and  Varnishes.     G.  H.  Hurst,  London,  1892.     (Griffin 

&  Co.) 
The  Chemistry  of  Paints  and  Painting.     A.  H.  Church.     2d  Ed.      London, 

1892.  (Seeley  &  Co.) 

Le  Caoutchouc  et  la  Gutta-percha  a  L' Exposition  Universelle,  de  1889.    Ren6 

Bobet,  Paris,  1893. 

Pigments,  Paints,  and  Painting.     G.  Terry,  London,  1893.     (Spon  &  Co.) 
Fabrication  des  Vernis.     L.  Naudin,  Paris,  1893. 
Journal  of  the  Society  of  Chemical  Industry.     1894.     C.  0.  Webber. 
Die  Fabrikation  der  Copal-,  Turpentinol-  und  Spiritus-Lacke.     L.  E.  Andes. 

2te  Auf.     Wien,  1895.     (Hartleben.) 
Couleurset  Vernis.    G.  Halphen,  Paris,  1895. 

Die  Harze  und  ihre  Producte.     G.  Thenius,  Wien,  1895.     (Hartleben.) 
Gummi  arabicum  u.  dessen  Surrogate  in  festem  u.  fliissigem  Zustande.     L.  E. 

Andes,  Wien,  1896.     (Hartleben.) 


STARCH,   DEXTRIN,   AND   GLUCOSE  353 

STARCH,  DEXTRIN,  AND  GLUCOSE 

Starch  is  widely  and  abundantly  distributed  in  the  vegetable 
kingdom,  occurring  in  nearly  all  plants  in  a  greater  or  less  quantity. 
It  forms  rounded  grains  of  characteristic  appearance  in  the  several 
varieties,  and  is  most  abundant  in  the  fruit,  tubers,  seeds,  and  stems 
of  the  plants  from  which  it  is  industrially  obtained.  It  is  a  typical 
carbohydrate,  and  on  analysis  corresponds  to  the  formula  C6H1005 ; 
but  it  is  probable  that  the  true  symbol  is  some  multiple  of  this,  and 
that  the  formula  should  be  written  (C6H10O5)W  where  n  is  4  or  more. 
Starch  has  not  yet  been  prepared  synthetically,  and  even  its  for- 
mation in  plants  is  not  fully  understood ;  but  it  appears  that  the 
chlorophyl  (the  green  coloring  matter  in  plants)  enters  into  the 
reaction  in  some  way,  perhaps  as  a  "contact"  substance.  The 
carbon  dioxide  of  the  air  is  reduced  by  the  joint  action  of  the 
chlorophyl  and  sunlight,  the  carbon  being  assimilated,  and  part  of 
the  oxygen,  at  least,  being  set  free.  The  formation  of  starch  might 
be  represented  thus :  — 

6  C02  +  5  H20  =  C6H1005  +.6  O2. 

It  is,  however,  probably  not  formed  directly,  but  may  be  an  alter- 
ation product  of  the  sugar  which  is  so  formed.  As  hypothetical 
reactions,  the  following  will  serve  to  show  the  outline  of  the  process, 
but  it  is  by  no  means  certain  that  these  truly  represent  the  exact 
changes  which  occur :  — 

6  C02  +  6  H20  =  C6H1206  +  6  O* 
CeHjA  =  C6H]005  +  H20. 

It  appears  somewhat  improbable  that  substances  of  such  high 
molecular  weight  as  glucose,  C6Hli506,  or  starch,  should  be  formed 
directly  from  the  reduction  of  carbon  dioxide.  According  to  Baeyer,* 
it  is  more  probable  that  formaldehyde,  CH2O,  is  first  produced,  and 
then  by  a  polymerization  process,  the  glucose  is  formed,  from  which 
starch  is  derived :  — 

6C02  +  6H20  =  6CH20  +  602. 
6CH2O  =  C6H1206. 

The  starch  is  formed  in  the  leaves  and  green  parts  of  the  plant, 
being  then  transported  in  soluble  form  to  the  other  parts,  where  it  is 
at  once  applied  to  the  building  up  of  the  tissues,  or  is  deposited  as 

*  Berichte  der  deutchen  chemischen  Gesellschaft,  3,  67. 

2A 


354  OUTLINES  OF  INDUSTRIAL   CHEMISTRY 

reserve  material  for  the  future  nourishment  of  the  plant,  or  of  a  new 
individual ;  the  greatest  deposits  are  generally  found  in  the  roots, 
tubers,  or  seeds. 

As  seen  under  the  microscope,  a  starch  granule  is  made  up  of 
different  layers,  arranged  around  a  nucleus,  a  dark  interior  portion, 
generally  at  one  side  of  the  granule.  Each  granule  consists  of  an 
interior  substance  called  "  granulose,"  and  an  exterior  transparent 
covering,  inert  and  insoluble,  and  resembling  cellulose  in  structure. 
But  recent  investigations  tend  to  prove  that  the  "  starch  cellulose  " 
is  not  present  as  such  in  the  granule,  but  is  formed  from  the  starch 
substance  by  the  action  of  acids  or  by  fermentation. 

Starch  is  entirely  insoluble  in  cold  water,  but  when  heated  to 
70°  or  80°  0.,  the  granules  swell  and  finally  burst,  and  the  starch 
substance  "granulose,"  combines  with  the  water  to  form  paste. 
When  this  is  boiled  in  an  excess  of  water,  it  goes  into  solution  and 
may  be  filtered.  The  solution  yields  an  intense  blue  color  with 
iodine,  hence  its  use  as  an  "  indicator " ;  it  is  optically  active  and 
rotates  the  plane  of  polarization  to  the  left. 

By  exposing  starch  to  the  action  of  cold  dilute  mineral  acid  for 
several  days,  it  is  converted  into  a  soluble  modification  called 
amylodextrin,  which  dissolves  in  warm  water  without  forming  a 
paste.  When  heated  dry  to  200°  C.,  starch  is  converted  into  dex- 
trine or  British  gum. 

The  chief  industrial  sources  of  starch  are  potatoes,  wheat,  corn, 
rice,  arrowroot,  and  certain  varieties  of  palm  trees  (sago).  In 
Europe,  potatoes,  rice,  and  wheat  are  used,  while  in  this  country 
corn  and  wheat  are  mainly  employed.  The  separation  of  the  starch, 
which  is  mixed  with  various  nitrogenous  and  fatty  matters  and 
some  mineral  impurities,  is  essentially  a  mechanical  process;  but 
much  care  is  needed  to  prevent  changes  which  would  spoil  the 
product. 

Corn  starch*  is  usually  made  by  the  alkaline  or  "  sweet"  process ; 
sometimes  by  an  acid  or  fermentation  method  similar  to  that  em- 
ployed for  wheat  starch.  In  the  alkaline  process  the  grain  is  run 
through  a  fanning  mill  to  blow  away  dust,  husks,  etc.,  and  is  then 
steeped  in  water  at  from  70°  to  140°  F.  for  from  three  to  ten  days, 
when  the  softened  grains  are  crushed  between  rolls.  This  steeping 
removes  much  of  the  oil  and  swells  the  gluten  and  albuminous  matter 
so  that  it  is  readily  attacked  by  the  alkali.  After  a  time  putrefactive 
fermentation  sets  in  and  hydrogen  sulphide  is  evolved.  Since  this 
causes  a  nuisance,  the  method  has  been  replaced  in  some  factories 
*  J.  Soc.  Chem.  Ind.  1887,  80.  Geo.  Atchbold. 


STARCH,  DEXTRIN,  AND   GLUCOSE  355 

by  the  Durgen  system,  in  which  a  continuous  stream  of  water  at 
130°  to  140°  F.  flows  slowly  through  the  steeping  tanks.  After 
three  days  the  grain  is  soft,  while  a  large  quantity  of  extractive 
matter  has  been  washed  away.  The  grain  is.  then  ground  in  buhr- 
stone  and  roller  mills  through  which  water  is  flowing ;  the  starchy 
magma  goes  to  revolving  sieves  of  brass  wire  for  the  coarser  strain- 
ing, and  then  to  cylindrical  reels  covered  with  bolting  cloth.  The 
mass  which  passes  over  the  sieves  is  reground  and  again  sifted. 
The  waste  glutinous  matter  is  pressed  and  dried  for  cattle  feeding, 
or  is  sold  wet  as  "  swill "  for  hogs.,2? 

<^s  The  milky  liquor  from  the  sieves  is  settled  and  drawn  off  from 
the  crude  starch,  which  is  washed  twice  with  fresh  water  and  then 
pumped  into  vats  having  good  stirring  apparatus,  and  provided  with 
holes  in  the  sides,  closed  by  plugs  and  used  for  decanting  the  liquor. 
A  dilute  caustic  soda  solution  of  7  or  8°  Be.  is  stirred  into  the  starch 
until  the  liquid  becomes  greenish-yellow ;  then  the  whole  is  stirred 
for  several  hours.  When  a  test  shows  that  the  suspended  matter 
settles  in  two  layers,  the  starch  on  top,  sedimentation  is  allowed  to 
take  place  and  the  supernatent  liquor,  containing  much  oil  and 
nitrogenous  matter  in  solution,  is  drawn  off.  The  sediment  is 
stirred  up  with  water,  allowed  to  stand  until  the  gluten  has  de- 
posited, and  then,  by  pulling  the  plugs  in  succession,  the  starch  in 
suspension  is  "siphoned  off"  into  tanks.  By  several  repetitions 
of  this  process  the  starch  is  nearly  all  removed  from  the  gluten  and 
at  the  same  time  is  separated  into  several  grades.  The  residue  then 
flows  onto  a  long,  slightly  inclined  table,  or  "  run,"  from  60  to  120 
feet  long  and  having  a  fall  of  3  or  4  inches.  A  stream  of  water 
flows  slowly  over  it  and  washes  away  the  gluten  and  fibrous  matter, 
while  the  starch  deposits  on  the  table. 

The  starch  collected  in  the  several  tanks  is  washed  with  water 
and  sometimes  again  siphoned,  and  is  then  run  through  bolting 
cloth  to  the  settling  tanks,  where  it  deposits  in  a  dense  compact 
layer  from  which  the  water  can  be  drawn  off  very  completely.  The 
wet  starch  is  then  shovelled  into  frames  lined  with  cloth  and  having 
perforated  bottoms,  through  which  the  water  drains.  The  cake  of 
damp  starch  is  cut  into  smaller  blocks  and  placed  on  porous  floors 
of  plaster  of  Paris  or  brick,  which  absorb  the  adhering  water.  *  The 
starch  is  removed  to  the  dry  room  and  kept  at  a  temperature  of 
125°  F.  for  several  days.  While  it  is  drying,  the  impurities  still 
remaining  in  it  find  their  way  to  the  surface,  where  they  form  a 

*  These  floors  may  be  subsequently  dried  by  passing  hot  air  through  flues  ar- 
ranged in  them. 


356  OUTLINES  OF   INDUSTRIAL   CHEMISTRY 

yellowish  deposit  which  is  cut  away  when  the  starch  is  nearly  dry. 
The  block  is  then  wrapped  in  paper  and  further  dried  at  150°  to 
170°  F.  for  several  days.  During  this  time  the  mass  contracts  and 
cracks  into  a  number  of  irregularly  shaped  prismatic  rods,  called 
"crystals,"  though  they  are  not  true  crystals.  The  entire  drying 
process  requires  several  weeks,  and  the  product  as  sent  to  market 
contains  about  10  to  12  per  cent  of  water. 

In  recent  working  the  process  is  so  modified  that  the  corn  oil 
can  be  saved.  After  careful  steeping,  the  grain  is  coarsely  ground 
and  the  meal  is  agitated  with  water  in  long  troughs;  the  husks  and 
germ,  being  lighter  than  the  starchy  portions,  are  floated  off.  These 
contain  the  most  of  the  oils,  nitrogenous  matter  (gluten),  and  albu- 
minoids of  the  grain,  and  are  treated  to  extract  the  corn  oil  (p.  310), 
or  dried  for  cattle  food. 

Sometimes  sulphurous  acid  is  added  to  the  water  used  for  steep- 
ing, in  order  to  prevent  putrefactive  fermentation,  and  also  to  bleach 
the  starch.  The  settling  tanks  may  be  replaced  by  two  or  three  long 
tables  set  at  a  very  slight  incline.  The  milky  fluid  passes  down  one 
table,  depositing  a  large  part  of  its  starch,  while  most  of  the  fibrous 
and  albuminous  matter  remains  in  suspension  and  passes  to  another 
table,  where  a  poorer  grade  of  starch  is  deposited. 

Centrifugal  machines  have  recently  come  into  use  for  separating 
the  starch  from  the  wash  water.  These  machines  are  of  two  kinds, 
those  having  a  perforated  basket,  and  those  in  which  the  basket 
is  of  unperforated  sheet  metal.  In  the  latter,  the  starch  is  thrown 
against  the  cylinder  wall  and  packed  so  firmly  that  it  remains  as 
a  thick  layer,  while  the  water  collects  in  the  middle  of  the  drum 
and  can  be  drawn  off  very  completely,  carrying  with  it  much  of  the 
glutinous  and  fibrous  matter.  In  a  perforated  drum  the  water 
passes  through,  leaving  the  solid  matter  behind.  The  starch,  being 
heavier  than  the  cellulose,  forms  a  layer  directly  on  the  basket 
walls,  while  inside  of  this  is  a  layer  of  gray  starch  containing  the 
impurities ;  this  latter  is  scraped  off  and  washed  again.  The  starchy 
liquid  running  into  the  basket  must  not  be  too  thick,  otherwise  the 
load  does  not  distribute  itself  evenly  in  the  basket. 

Corn  contains  about  54  per  cent  of  starch,  and  the  actual  yield 
obtained  in  technical  work  is  about  50  per  cent,  or  28  pounds  of 
starch  from  a  bushel  (56  pounds)  of  corn.  About  13  pounds  of 
gluten  suitable  for  cattle  food  is  also  recovered  per  bushel  of  corn. 

The  best  grade  of  corn  starch  is  largely  consumed  for  food,  but 
its  principal  use  is  in  laundry  work.  Lower  grades  are  chiefly 
employed  in  manufacturing  and  in  textile  industries.  In  many 


STARCH,   DEXTRIN,   AND   GLUCOSE  357 

technical  operations  the  so-called  "  green  starch "  is  used.  This  is 
the  product  obtained  directly  from  the  centrifugal  machine,  inclined 
table,  or  settling  tanks  after  a  partial  drying.  It  contains  some 
impurities  and  is  generally  damp,  often  containing  40  per  cent  of 
water.  It  is  mainly  employed  for  glucose  making,  for  stiffening  and 
size,  in  color  mixing  for  calico  printing,  and  in  the  manufacture  of 
paper  boxes. 

OUTLINE  OF  THE  PROCESS  FOR  CORN  STARCH 
Cornv    ^/^  *j*   &*»*& 


|   <T  **"-  ~   I  \ 

(A)  Steeped 

(5)  Crushed 

(<7)  Germ  Separators 

Germ  Corn  Meal 

Ground  Ground  fine  (buhrstones) 

Pressed  Passed  twice  over  shakers  which 
| are  sprinkled  with  water 

Oil  cake.        Corn  oil.  \  | 

(E)  Starch  water  (Z>)  Husks. 


h 


Carries  starch  and  gluten  Reground  (steel  rolls) 

Agitated  in  tank  "Slop"  passed  through  slop 

(Qx^-voJ                 j  machine,   a  wringer  to  re- 

Fed  to  "runs"  or  tables  move  residual  starch  water 
(120  ft.  by  2  ft.,  with 


gentle  incline) 

Starch  water 

Wet  feed 

T)              1 
Consists   of 
husk  and  bits 
of  germ 

Passed  to  dry 
room 

Dry  Feed 

Gluten 
Settled 

• 

|       returned  to  (Z 
Starch 

Liquor 
Rejected 

1 
Gluten      .' 

Filter-pressed 

Cake  ground  and  passed 
through  driers 

Process  generally  repeated 
Cooled 


358  OUTLINES   OF  INDUSTRIAL   CHEMISTRY 

Wheat  starch  is  made  by  the  fermentation  or  "  sour  "  process,  or 
by  Martin's  process  without  fermentation. 

By  the  sour  process,  all  the  gluten,  of  which  wheat  contains  a 
large  amount,  is  destroyed,  consequently  there  is  considerable  loss. 
The  grain  is  soaked  in  water  until  soft,  and  then  crushed  between 
rolls  or  pressed  in  bags.  The  starch  is  washed  out  of  the  crushed 
pulp  with  water,  and  the  milky  liquid  is  run  into  tanks  and  allowed 
to  ferment.  In  order  to  hasten  this,  some  of  the  sour  liquor  from  .a 
previous  fermentation  is  added.  The  temperature  is  kept  at  about 
20°  C.,  and  the  contents  of  the  cistern  well  stirred  frequently.  The 
fermentation  lasts  from  1.0  to  14  days;  the  sugar,  albumin,  and 
gummy  matters  of  the  wheat  undergo  an  alcoholic  fermentation, 
followed  by  the  development  of  acetic,  lactic,  and  butyric  acids. 
These  acids  then  attack  the  gluten,  dissolving  it  in  part,  and  de- 
stroy its  tough  and  sticky  properties,  so  that  it  is  easily  washed 
free  from  the  starch.  The  washing  is  done  in  revolving  sieves,  in 
which  the  swollen  gluten,  cellulose,  etc.,  remain.  The  starch  is  re- 
peatedly washed  and  sieved,  or  levigated,  until  sufficiently  pure  and 
white,  when  it  is  dried  as  already  described  under  corn  starch ;  but 
more  care  is  necessary,  because  of  the  tendency  of  the  mass  to  cake 
together,  owing  to  the  presence  of  a  trace  of  gluten.  The  process 
must  be  carefully  watched  lest  the  fermentation  go  too  far  and 
putrefaction  set  in,  thus  causing  a  loss  of  starch.  The  acid  waste 
liquors  are  difficult  to  dispose  of,  and  cause  considerable  nuisance 
in  the  neighborhood.  Usually  about  59  pounds  of  starch  and  11 
pounds  of  bran  are  obtained  from  100  pounds  of  wheat.  But  only 
a  small  quantity  of  sour  gluten  is  recovered. 

By  Martin's  process  part  of  the  nitrogenous  matter  (gluten)  is 
recovered.  Ordinary  wheat  flour  from  which  the  bran  has  been 
removed  is  used  instead  of  the  whole  grain.  The  flour  is  kneaded 
with  40  per  cent  of  water  to  form  a  stiff  dough,  which  is  then 
washed  in  small  portions  at  a  time  in  a  fine  sieve,  while  small  jets 
of  water  continually  play  upon  the  mass,  carrying  away  the  starch.. 
By  treating  the  partly  washed  starch  with  a  solution  of  caustic 
soda  (sp.  gr.  1.013)  and  allowing  it  to  stand  a  few  hours,  the  remain- 
ing gluten  is  swollen  and  may  be  removed  by  sieving  on  bolting 
cloth.  The  pasty  mass  of  gluten  left  in  the  sieves  is  utilized  in  the 
manufacture  of  macaroni,  noodles,  and  gluten  bread,  but  more  espe- 
cially for  paste  and  for  cement  for  leather,  and  as  a  thickening 
material  instead  of  casein  or  albumin  in  textile  working. 

Fesca's  modification  of  Martin's  process  consists  in  stirring  wheat 
flour  into  water  to  form  a  thin  "  milk,"  which  is  then  run  into  cen- 


STARCH,   DEXTRIN,   AND   GLUCOSE  359 

trifugal  machines.  The  starch,  being  heavier  than  the  gluten,  col- 
lects next  the  revolving  sieve.  The  interior  layer,  consisting  of  a 
mixture  of  starch  and  gluten,  is  removed,  washed  with  water,  and 
again  "  centriffed."  But  much  starch  remains  in  the  gluten. 

The  yield  by  Martin's  method  is  about  55  pounds  of  starch  and 
12  pounds  of  gluten  from  100  pounds  of  wheat.  By  Fesca's  process, 
only  40  to  45  pounds  of  starch  are  obtained  from  100  pounds  of  wheat. 

Potato  starch  is  very  important  in  Europe.  The  tubers  contain 
an  average  of  about  20  per  cent  of  starch  and  75  per  cent  water. 
The  skin  contains  some  fats  and  coloring  matter,  but  no  starch. 
The  adhering  dirt  and  sand  are  carefully  removed  by  washing  in 
a  revolving  drum  made  of  wood  or  iron  slats  with  narrow  openings 
between  them  for  the  escape  of  the  dirt,  etc.  Inside  the  drum  are 
revolving  arms  which  rub  the  potatoes  together,  or  revolving  wire 
or  bristle  brushes  which  scrub  them  as  the  drum  turns.  The  wash- 
ing must  be  very  thorough  or  the  quality  of  the  starch  suffers. 
The  tubers  are  next  rasped  or  ground  in  a  machine  consisting  of 
a  revolving  cylinder  or  roll,  around  whose  outer  surface  are  set  a 
large  number  of  narrow  knife-edges  or  saw-blades,  which  project 
about  one-fifth  of  an  inch.  These  knife-edges  rotate  very  close  to 
fixed  wooden  bars  which  catch  and  hold  the  potato  while  it  is 
scraped  into  soft  pulp.  Another  kind  of  rasper  consists  of  a  fixed 
hollow  cylinder,  having  saw-blades  set  on  its  inner  surface,  against 
which  a  revolving  fork  rubs  the  potatoes. 

The  starch  in  the  potato  is  enclosed  in  little  cells  or  bags  of 
cellulose,  a  number  of  granules  being  in  each  cell.  Since  the  starch 
can  only  be  washed  away  from  the  ruptured  cells,  the  finer  the  pulp 
the  larger  the  yield  of  starch.  But  even  with  the  best  raspers  many 
cells  escape  unbroken,  and  usually  about  15  per  cent  of  the  starch  is 
lost.  Sometimes  the  pulp  is  reground  after  it  has  been  washed, 
which  increases  the  yield  of  starch  slightly. 

The  pulp,  consisting  of  starch  and  cellulose  fibre  and  tissue, 
passes  into  a  series  of  shaking  sieves,  where .  the  starch  is  washed 
away  with  a  limited  amount  of  water.  A  better  apparatus  consists 
of  a  series  of  revolving  wire  gauze  cylinders  (30  to  35  meshes  to  the 
inch),  containing  brushes  which  revolve  in  a  direction  opposite  to 
the  motion  of  the  cylinder.  Fine  jets  of  water  play  upon  the  pulp 
and  wash  out  the  starch.  The  milky  liquor  passes  to  a  revolving 
sieve  with  50  meshes  per  inch,  which  retains  any  fibre  that  passes 
through  the  coarser  screens.  Long  semicylindrical  sieves  contain- 
ing brushes  set  in  the  form  of  an  Archimedian  screw  around  a 


360  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

revolving  shaft  are  sometimes  used.  The  brushes  push  the  pulp 
along  from  one  end  to  the  other,  at  the  same  time  thoroughly  work- 
ing it  over,  while  the  starch  is  washed  out  by  jets  of  water. 

The  waste  pulp  passing  over  the  sieves  is  treated  by  Buttner  and 
Meyer's  process ;  it  is  pressed  and  dried  rapidly  until  the  moisture 
is  about  12  per  cent.  It  is  sold  as  a  low  grade  cattle  food.  The 
starch  suspended  in  the  wash  water  is  run  over  inclined  tables 
similar  to  those  already  described.  The  crude  product  is  stirred 
up  with  water  in  a  tank,  and  after  the  sand  and  heavy  dirt  has 
settled,  the  starch  in  suspension  is  rapidly  "  siphoned "  off  through 
holes  in  the  side  of  the  tank.  By  levigation,  the  starch  is  obtained 
in  several  grades  of  purity. 

Centrifugal  machines  are  also  employed  to  separate  the  starch 
and  wash  water,  but  with  less  success  than  in  the  case  of  corn, 
wheat,  or  rice  starch. 

The  crude  starch  obtained  by  any  of  these  methods  is  purified 
by  repeated  washings  and  levigation,  with  an  occasional  passing 
through  sieves  or  bolting  cloth  to  remove  fibre.  The  purified  starch 
is  dried  in  much  the  same  way  as  is  corn  starch. 

Potato  starch  is  also  made  by  the  "  rotting "  process,  in  which 
the  moist,  sliced  material  is  heaped  in  a  warm  room.  Fermentation 
and  ultimate  decomposition  of  the  cell  walls  takes  place,  so  that  the 
starch  can  be  washed  out  of  the  pulp.  Much  care  is  necessary  that 
the  fermentation  does  not  attack  the  starch  itself.  The  mass  must 
be  turned  over  frequently  during  decomposition. 

The  wash  waters  from  potato  starch  contain  much  potash,  phos- 
phoric acid,  albumin,  and  nitrogenous  matter,  which  soon  ferment 
and  become  very  offensive.  If  possible,  they  should  be  used  at  once 
to  irrigate  land.  Much  ingenuity  has  been  expended  to  devise 
means  of  making  them  less  offensive,  but  without  much  success. 

The  yield  from  100  pounds  of  potatoes  is  about  15  or  16  pounds 
of  dry  starch.  The  product  is  chiefly  used  in  the  textile  industries, 
for  laundry  purposes,  and  in  glucose  and  dextrine  making ;  for  the 
two  last  mentioned  it  is  customary  to  use  the  "  green  starch,"  con- 
taining from  30  to  40  per  cent  water. 

Rice  starch*  is  chiefly  produced  in  Europe,  only  the  broken 
grains  separated  with  the  husks  in  the  cleansing  mills  being  used. 
Bice  contains  nearly  80  per  cent  of  starch,  but  its  separation  is  very 
difficult,  since  the  cells  of  the  grain  are  composed  of  very  dense  glu- 
tinous material  and  the  starch  granules  are  cemented  together  very 
solidly  by  albuminous  and  gummy  matter.  In  order  to  soften  the 
*  J.  Berger,  Chem.  Zeitung,  14,  1440  and  1571 ;  15,  843. 


STARCH,   DEXTRIN,   AND   GLUCOSE  361 

gluten,  the  rice  is  macerated  in  very  dilute  caustic  soda  (sp.  gr.  1.007) 
containing  about  0.5  per  cent  caustic.  After  soaking  about  18  hours 
with  frequent  stirring,  the  liquor  is  drawn  off  and  a  fresh  caustic 
solution  is  added.  When  the  grain  is  soft  it  is  crushed  in  mills 
while  a  stream  of  dilute  caustic  plays  over  the  mass,  dissolving  a 
part  of  the  glutinous  matter,  and  swelling  the  remainder  so  that  it, 
together  with  the  fibrous  matter,  may  be  removed  by  sieving.  The 
starch  is  then  separated  from  the  liquor  by  centrifugal  machines, 
and  further  purified  by  washing  it  with  water,  running  it  through 
centrifugal  machines  or  settling  tanks,  and  finally  filter-pressing  and 
drying  in  much  the  same  way  as  for  corn  starch.  The  yield  is 
about  85  per  cent  of  the  total  starch  in  the  rice.  The  fibrous  matter 
and  gluten  passing  over  the  sieves  are  used  as  cattle  food,  or  if  care- 
fully dried  and  pulverized,  are  sometimes  sold  as  "rice  meal." 
The  caustic  solutions  contain  gluten  which  is  precipitated  by  acidi- 
fying them.  Much  care  is  necessary  to  prevent  any  fermentation  of 
the  liquors  or  of  the  wet  starch,  if  the  drying  be  too  slow.  In  order 
to  correct  the  slight  yellow  tinge,  due  to  traces  of  impurity  in  the 
starch,  a  little  ultramarine  is  generally  added  in  the  settling  tanks 
or  centrifugals.  Prussian  blue  or  alkaline  blues  which  are  not  fast 
against  alkali  should  not  be  used. 

Sago  is  a  starch  prepared  from  the  pith  of  several  varieties  of 
palm  trees  (genera  Metroxylon,  Arenga,  and  Borassus),  indigenous  in 
the  East  Indies.  The  trees  are  cut  down  and  the  pith,  sometimes 
amounting  to  700  pounds  from  one  tree,  is  removed  from  the  trunks. 
It  is  a  mixture  of  starch  and  woody  fibre  and  is  pounded  fine  in 
wooden  mortars ;  the  starch  is  washed  out  with  water  and  purified 
by  sieving  and  washing  as  in  other  cases.  This  furnishes  the  sago 
flour  of  commerce.  Pearl  sago  is  made  by  kneading  the  sago  flour  to 
a  dough  with  water,  and  then  working  the  dough  through  a  sieve 
into  a  hot  pan,  greased  with  oil,  and  kept  shaking  constantly  ;  a  por- 
tion of  the  starch  is  converted  into  paste  by  the  heat,  and  coats  the 
outside  of  the  granules,  which  then  stick  together  and  form  little 
translucent  globules.  Imitation  sago  is  now  made  from  potato  or 
other  starch.  Sago  is  chiefly  used  as  food  and  swells  in  hot  water 
without  destroying  the  globular  form. 

Arrowroot  *  starch  is  obtained  from  the  roots  of  several  varieties 
of  plants  belonging  to  the  genus  Maranta.  The  long  slender  roots 
are  soaked  in  water  until  the  coarse  outer  skin  softens,  when  it  is 
stripped  off.  After  washing,  the  roots  are  rasped  to  a  pulp,  from 
which  the  starch  is  washed  with  water,  sieved,  and  settled  to  remove 
*  J.  Soc.  Chem.  Ind.,  1887,  334. 


362  OUTLINES  OF   INDUSTRIAL   CHEMISTRY 

fibrous  matter  and  soluble  impurities.  Owing  to  the  large  amount 
of  fibre  present,  fine  grinding  is  difficult,  and  considerable  starch  is 
lost  in  the  waste  pulp.  Also,  there  is  much  trouble  in  sieving; 
hand  sieves  are  used,  since  mechanical  ones  soon  become  choked  by 
the  fibres.  The- starch  is  dried  in  the  open  air  on  wire  screens  until 
no  more  than  14  to  17  per  cent  of  water  remains.  The  drying  house 
is  a  light  shed,  open  on  all  sides  for  the  free  circulation  of  air.  In 
damp  weather  much  care  is  necessary  to  keep  the  wet  starch  from 
souring,  especially  if  any  impurity  is  present.  Arrowroot  starch  is 
much  used  for  food,  but  is  also  desirable  for  laundry  and  sizing  pur- 
poses. It  forms  a  stiff er  jelly  than  do  most  other  starches. 

Cassava  starch  is  similar  to  arrowroot  and  is  obtained  from  the 
roots  of  several  species  of  Maniliot,  which  are  indigenous  in  Brazil, 
but  which  are  now  cultivated  in  other  tropical  countries.  The 
starch  is  also  called  Brazilian  arrowroot  and  is  prepared  similarly 
to  the  true  arrowroot.  By  heating  the  damp  starch  in  shallow  pans 
while  stirring  actively,  the  granules  burst  and  adhere  together,  form- 
ing the  mass  into  small,  irregularly  shaped  translucent  kernels,  known 
as  tapioca.  This  is  somewhat  soluble  in  cold  water,  and  is  very 
easily  swelled  by  boiling  water  to  form  a  transparent  jelly. 

There  are  several  other  starches  similar  to  sago  and  cassava  which 
are  used  as  food,  the  most  important  of  these  being  curcuma,  tous- 
les-mois  and  arum.  Some  starch  is  prepared  from  the  nuts  of  the 
horse-chestnut  tree,  JEsculus  Hippocastanum,  L.,  which  contains  about 
25  per  cent  of  starch.  But  since  it  is  nearly  impossible  to  remove 
the  bitter  principles,  the  starch  is  only  used  for  stiffening  and  sizing 
purposes. 

The  chief  uses  of  starch  are :  for  stiffening  purposes  in  laundry 
work  and  finishing  cotton  cloth  —  rice  starch  is  best  for  this  and  the 
addition  of  a  little  parafnne  or  stearin  increases  the  gloss ;  for 
thickening  material  in  calico  printing ;  as  paste  for  adhesive  pur- 
poses —  for  which  wheat  starch  is  best ;  in  sizing  paper ;  for  glucose 
making,  in  which  corn  or  potato  starch  is  generally  used  ;  as  a  food ; 
and  as  a  toilet  powder,  for  which  rice  starch  is  generally  pre- 
ferred. 

Starch  is  readily  detected  by  the  microscope  or  by  use  of  a  solu- 
tion of  iodine.  There  are  several  methods  for  determining  the 
amount  of  starch  in  a  given  substance,  but  nearly  all  of  them  de- 
pend upon  the  direct  isolation  of  the  starch,  or  its  conversion  into 
sugar,  which  is  then  determined  by  means  of  Fehling's  solution. 


STARCH,   DEXTRIN,   AND   GLUCOSE  363 

DEXTRIN 

Dextrin  corresponds  to  the  formula  (C^H^Ou^  and  is  some- 
times considered  an  intermediate  product  between  starch  and 
dextrose.  The  commercial  product,  called  dextrine,  or  British 
gum  is  made  by  heating  dry  starch  to  a  temperature  of  200°  to 
250°  C.  in  a  revolving  iron  cylinder  over  free  flame,  or  in  an  oil 
bath,  or  by  a  steam  jacket;  or  the  starch  may  be  moistened 
with  nitric  or  hydrochloric  acid,  dried  at  50°  C.  and  then  heated 
to  140°  to  170°  C. ;  this  gives  a  lighter  colored  product,  but  since 
it  contains  some  sugar,  its  adhesive  power  is  less  than  if  made 
without  acid.  After  roasting,  the  dextrine  is  cooled  quickly  to 
stop  the  conversion,  and  is  powdered  in  a  mill  and  sieved  on  bolting 
cloth.  The  product  is  an  indefinite  mixture  of  several  dextrins 
with  unchanged  starch.  The  dextrins  are  soluble  in  cold  water  and 
form  a  thick  viscous  syrup  which  has  strong  •  adhesive  properties 
and  is  therefore  much  used  as  a  substitute  for  gum  Arabic  in  pre- 
paring mucilage  and  for  thickening  colors  in  calico  printing. 

By  acting  upon  starch  paste  with  diastase,  a  syrupy  liquid  con- 
taining dextrin  and  sugar  (maltose)  is  obtained;  starch  is  mixed 
with  water  at  50°  C.,  and  then  heated  to  65°  C.,  when  the  necessary 
amount  of  malt  (carrying  the  diastase)  is  added,  and  the  temperature 
raised  to  73°  C.,  until  iodine  gives  a  reddish  violet,  instead  of  a  blue 
color.  The  solution  is  then  boiled  to  destroy  any  remaining  diastase, 
cooled,  filtered,  and  concentrated  in  vacuo  to  the  desired  density. 
It  is  established  that  there  are  several  dextrins  produced  simul- 
taneously with  the  formation  of  the  sugar  by  this  action.  Dextrin 
syrups  are  used  in  brewing,  for  thickening  tanning  extracts,  and  in 
confectionery. 

The  products  obtained  by  these  various  methods  vary  somewhat 
in  their  properties,  and  have  been  assigned  distinguishing  names,  — 
erythrodextrin,  achroodextrin,  and  maltodextrin.  They  are  all 
soluble  in  water,  insoluble  in  alcohol,  strongly  dextro-rotary,  and 
yield  dextrose  by  hydrolysis.  Erythrodextrin  yields  a  red  color 
with  iodine,  while  the  others  yield  no  color. 


GLUCOSE 

Under  the  name  "  glucose  "  are  grouped  not  only  substances  de- 
rived from  starch  by  hydrolysis,  such  as  dextrose,  maltose,  dextrins, 
etc.,  but  also  those  resulting  from,  the  inversion  of  sugar,  such  as 
laevulose. 


364  OUTLINES  OF  INDUSTRIAL   CHEMISTRY 

Dextrose,  C6H1206,  and  the  isomeric  laevulose  occur  in  the  juice 
of  many  fruits,  such  as  grapes,  cherries,  bananas,  pears,  etc.,  but  in 
quantities  varying  even  in  the  same  fruit,  according  to  the  season 
and  their  degree  of  ripeness.  But  these  sugars  are  very  seldom  pre- 
pared from  fruit  juice,  being  more  easily  obtained  from  starch,  from 
which  the  most  of  the  so-called  "  fruit  sugar  "  and  "  grape  sugar  "  of 
commerce  are  made. 

Common  honey  is  a  mixture  of  dextrose,  Isevulose,  dextrin,  and 
saccharose  (cane  sugar),  extracted  already  formed,  from  the  plant  by 
the  bee. 

Dextrose  is  less  soluble  in  water  than  is  cane  sugar,  but  does  not 
crystallize  readily  from  solution.  When  crystallized  at  moderate 
temperatures,  it  contains  one  molecule  of  crystal  water ;  but  from 
hot  water  or  from  alcohol  it  separates  in  the  anhydrous  state.  It  is 
a  little  more  than  half  as  sweet  as  sugar,  and  yields  an  anhydride, 
C6H1005  (glycosan),  which  is  tasteless.  Dextrose  rotates  the  plane 
of  polarization  to  the  right  52.5°.  It  is  readily  fermentable,  and 
reduces  alkaline  copper  solutions  (Fehling's  solution).  It  occurs  in 
nature  in  combination  with  other  organic  substances,  forming  the 
"glucosides." 

Laevulose  is  very  soluble  in  water,  but  crystallizes  from  alcohol 
without  crystal  water.  It  rotates  the  plane  of  polarization  of  the 
light  ray  very  strongly  to  the  left  (about  —92°),  but  the  rotation  is 
variable  with  the  concentration  and  temperature.  It  has  a  very 
sweet  taste,  and  is  very  easily  fermented  by  yeast.  It  also  reduces 
alkaline  copper  solution. 

Maltose,  see  p.  398. 

Commercial  glucose  is  always  prepared  from  starch  as  the  cheap- 
est and  most  convenient  raw  material.  By  boiling -starch  paste  with 
mineral  acids,  it  is  converted  into  dextrin,  maltose,  and  dextrose,  the 
amount  of  the  last  depending  upon  the  time  of  the  boiling.  The 
acid  does  not  appear  to  enter  into  the  reaction,  but  merely  assists 
the  combination  between  the  starch  and  water,  by  which  the  glucose 
is  formed.  This  is  a  process  of  "  hydrolysis."  It  might  be  repre- 
sented by  an  equation :  — 

(C6H1005)  n  +  nH20  =  n  (C6H1206), 

but  this  does  not  represent  the  changes  which  actually  occur,  for  a 
f  number  of  intermediate  products  .  are  formed ;  of  these,  the  dex- 
trin is  never  entirely  converted  into  sugar,  some  remaining  un- 
changed in  the  commercial  glucose.  The  yield  of  dextrose  is  seldom 
more  than  85  or  90  per  cent  of  the  theoretical,  as  calculated  from  the 


STARCH,   DEXTRIN,   AND  GLUCOSE 


365 


above  equation.  The  best  conversion  is  obtained  with  hydrochloric 
acid,  which  is  generally  used  in  this  country,  but  in  Germany  sul- 
phuric acid  is  used,  as  it  is  more  readily  separated  from  the  product. 
In  Europe  potato,  rice,  and  sago  starch  are  chiefly  used  for  glucose 
making,  but  in  this  country  corn  starch  is  exclusively  employed. 
It  is  used  "  green,"  and  is  prepared  on  the  premises.  The  corn  is 
steeped  from  3  to  5  days  in  water  at  150°  F.,  with  the  addition  of 
250  gallons  of  sodium  bisulphite  liquor  of  8°  Be.  to  each  2000 
bushels  of  corn ;  the  starch  is  then  prepared  as  described  on  p.  356. 

The  process  of  making  glucose  varies  slightly,  according  as 
syrup  or  solid  grape  sugar  is  to  be  the  final  product.  For  syrup, 
less  acid  is  used,  and  the  boiling  is  stopped  as  soon  as  a  test  with 
iodine  gives  a  port- wine  color.  This  may  leave  a  large  amount  of 
dextrin  in  the  product.  For  solid  dextrose,  the  boiling  is  continued 
until  alcohol*  causes  no  precipitate  to  form  in  a  test  portion  of  the 
liquid. 

For  the  conversion,  the  starch  is  stirred  with  water  in  a  tub,  to 
form  a  "  milk  "  of  about  20  °  Be.  Sometimes  a  part  of  the  acid  is 
added  to  this  milk,  and  the  mixture  warmed  to  about  38°  C.  It  is 
then  pumped  in  a  small  stream  into  the  boiling  dilute  acid  (1  to  3 
per  cent  acid)  contained  in  the  converter,  the  rate  of  inflow  being  so 
regulated  that  the  boiling  of  the  acid  liquid  is  not  interrupted. 

The  converter  may  be  an  open  vat  of  wood,  lined  with  lead,  and 
provided  with  stirring  apparatus  and  steam  coils.  But  open  con- 


FIG.  86. 

verters  are  now  abandoned  nearly  everywhere  in  favor  of  closed 
converters  (Fig.  86).  These  are  usually  made  of  cast  iron,  cop- 
per, or  wood,  strong  enough  to  withstand  a  pressure  of  5  or  6 
atmospheres.  Steam  at  25  to  30  pounds  pressure  is  admitted 
*  Starch  and  dextrin  are  precipitated  by  alcohol,  but  dextrose  is  not. 


366 


OUTLINES  OF  INDUSTRIAL   CHEMISTRY 


through  the  perforated  copper  pipe  (A).  The  starch  milk  is  pumped 
in  through  the  copper  pipe  (B)  [the  dilute  acid  having  been  pre- 
viously introduced  through  (D)],  the  air  vent  (V)  being  opened 
at  this  time,  while  the  pressure  is  kept  at  25  pounds.  As  soon 
as  the  converter  is  full,  the  air  vent  is  closed,  and  the  pressure 
is  raised  to  30  pounds  for  about  40  minutes,  or  until  the  iodine 
test  shows  that  the  conversion  is  complete.  For  syrup,  the  average 
time  elapsing  from  the  beginning  of  the  starch  introduction  to  the 
discharge  of  the  converter  is  about  1  hour  and  10  minutes,  and  the 
density  of  the  liquid  about  16°  Be. ;  for  grape  sugar,  about  an  hour 
and  a  half  is  necessary,  with  the  above  pressure  and  amount  of  acid. 
The  liquid  is  now  cloudy,  and  cannot  be  clarified  by  filtration.  The 


FIG.  8T. 

valve  (0)  is  opened,  and  the  liquid  is  blown  through  the  pipe  (C) 
into  the  neutralize?.  The  converter  is  provided  with  a  waste  pipe 
(F)  for  cleaning  purposes.  The  neutralizer  is  a  tank  (Fig.  87) 
provided  with  an  effective  stirring  apparatus  (A,  A).  Immediately 
after  the  converter  liquid  has  been  received  into  the  neutralizer  it 
is  treated  with  sodium  carbonate  solution,*  introduced  through 
the  sprinkler  (B),  to  remove  the  excess  of  acid.  It  is  left  very 
slightly  acid  to  litmus,  a  pinkish  lilac  color  being  about  right.  If 
made  alkaline,  the  syrup  becomes  colored  in  the  char  filtration,  and 
if  too  acid,  it  has  a  turbid  appearance.  Much  of  the  dissolved 
gluten  is  precipitated  during  the  neutralizing,  and  forms  a  greenish 
drab  scum. 

The  liquid,  called  "light  liquor,"  is  then  run  through  bag  filters 
to  remove  suspended  impurities,  and  the  clear,  amber-colored  liquid 
is  then  run  through  bone-char  filters,  displacing  the  "heavy  liquor" 

*  In  Europe  powdered  chalk  is  often  used  to  neutralize  the  sulphuric  acid,  the 
precipitate  of  calcium  sulphate  being  separated  from  the  liquor  by  filter-pressing. 


STARCH,   DEXTRIN,   AND   GLUCOSE  367 

for  which  the  filters  have  previously  been  used.  About  8000  gallons 
of  "light  liquor"  is  run  through  16  tons  of  bone-char,  which  has 
been  used  to  clarify  about  3500  gallons  of  "heavy  liquor.'7  The 
filtrate  is  colorless,  or  faintly  amber-colored,  and  has  a  slightly  acid 
reaction.  It  is  now  concentrated  in  the  Yaryan  triple  effect  evapo- 
rator to  a  density  of  27°  to  28°  Be.,  when  it  forms  the  "heavy  liquor" 
above  mentioned.  The  bone-char  in  the  filter  is  freshly  calcined, 
dusted,  and  "tempered"  with  acid,  and  washed  with  water.  The 
wash  water  is  removed  by  compressed  air,  and  the  filter  is  filled  with 
the  heavy  liquor.  After  standing  about  an  hour,  the  outlet  pipe  is 
opened,  and  the  filtrate  runs  out  in  a  slow  stream,  while  more  unfil- 
te.red  liquid  enters.  The  flow  is  secured  by  the  hydrostatic  pressure 
of  the  liquid  entering  the  filter  from  a  tank  elevated  above  it.  The 
filtrate  is  practically  colorless,  and  has  a  very  faint  odor.  It  is  con- 
centrated in  a  vacuum  pan  to  a  gravity  of  40°  to  44°  Be.  (1.375  to  1.43 
sp.  gr.).  During  this  evaporation  a  small  amount  of  a  solution  of 
sodium  bisulphite  (8°  Be.)  is  added  to  the  syrup  to  bleach  it,  and  to 
prevent  any  tendency  to  fermentation,  or  to  become  brown  when 
heated.  The  syrup,  composed  of  maltose,  dextrose,  and  dextrin,  is 
known  in  commerce  as  "  glucose  " ;  the  name  "  grape  sugar  "  is  applied 
to  the  solid  product  obtained  by  carrying  the  conversion  further. 
Grape  sugar  forms  a  compact  mass  of  waxy  texture,  but  containing 
no  separate  crystals  of  dextrose. 

A  method  for  the  production  of  crystallized  glucose  (dextrose)  has 
been  devised  by  Behr,  in  which  a  concentrated  glucose  solution  is 
allowed  to  stand  at  about  35°  C.  in  contact  with  some  crystals  of  pure 
anhydrous  dextrose,  until  a  large  part  of  the  dextrose  separates  as  a 
mass  of  crystals.  By  running  through  a  centrifugal  machine,  the 
uncrystallized  syrup  is  thrown  off,  leaving  the  pure  crystals.  If 
glucose  is  dissolved  in  hot  concentrated  methyl  alcohol,  on  standing 
the  solution  deposits  crystals  of  pure  anhydrous  dextrose. 

The  bone-char  niters*  used  for  glucose  are  cast-iron  cylinders, 
built  up  in  segments.  As  commonly  constructed  (Fig.  88)  one  holds 
about  16  tons  of  bone  black.  In  the  bottom  is  a  perforated  grating 
(A),  covered  with  burlap,  on  which  the  char  rests.  Beneath  this 
grating  is  the  outlet  pipe  (B),  which  is  carried  up  outside  the  filter 
to  the  level  of  the  top  of  the  char  when  the  filter  is  full.  By  this  r 
arrangement  no  liquor  flows  from  the  filter  until  the  char  is  entirely 
covered,  the  liquor  filters  slowly  and  with  less  tendency  to  form 
channels,  and  the  char  does  not  pack  nor  become  clogged.  On  one 

*  Similar  filters  are  used  for  filtering  sugar,  oils,  etc.  In  large  sugar  refineries 
they  hold  from  30  to  40  tons  of  bone-black. 


368 


OUTLINES  OF  INDUSTRIAL   CHEMISTRY 


side,  near  the  bottom,  is  a  manhole  through  which  the  exhausted 
char  is  removed.     In  the  top  is  another  manhole  for  introducing  the 

char,  and  also  an  inlet  pipe  (C)  for 
(f  If1  §•  §•  the  liquid  to  be  filtered,  another  (D) 
for  steam,  and  an  air  vent  (E).  A 
pipe  (G)  serves  for  the  introduction 
of  compressed  air,  to  assist  in  forc- 
ing the  liquor  or  wash  waters 
through  the  char  when  emptying 
the  filter,  and  for  running  off  the 
overflow  of  wash  waters  when  boil- 
ing out  the  char.  A  branch  (F), 
placed  in  the  outlet  pipe  directly 
below  the  filter,  permits  connection 
with  steam  through  (H),  or  with  a 
hot  water  pipe  (J),  to  be  used  in 
washing  the  char;  it  also  connects 
with  a  waste  pipe  (L),  through 
which  the  waste  liquors  can  be  run 
off.  The  inlet  pipe  (C)  is  so  ar- 
ranged that  it  may  be  connected 

by  means  of  a  rubber  hose  with  the  pipes  supplying  the  "light 
liquors"  (N),  "heavy  liquors"  (P),  wash  waters  (S),  or  tempering 
acid  (T).  The  outlet  pipe  (B)  is  also  connected  in  the  same  way 
with  pipes  leading  to  the  storage  tanks  for  the  filtered  syrups  and 
"sweet  water."  Below  the  lower  manhole  runs  an  endless  belt 
which  receives  the  spent  char  and  conveys  it  to  the  revivifying  kilns. 
The  bone-black  is  made  by  charring  bones  in  retorts,  and  then 
crushing  to  grains  about  2  or  3  mm.  in  diameter.  When  new  it  has 
a  velvety  black  or  brownish  color,  and  often  contains  traces  of  tar 
and  other  impurities.  After  it  has  been  used  a  few  times,  the  grains 
become  rounded,  and  many  of  the  impurities  are  washed  away.  The 
syrup  first  run  through  the  filter  is  completely  decolorized  by  the 
action  of  the  char;  but  after  a  time  its  decolorizing  power  is 
impaired,  and  the  filtrate  begins  to  show  a  faint  yellow  color. 
Finally  it  runs  so  deeply  colored  that  no  advantage  is  gained  by 
filtration.  Then  the  light  liquor  remaining  in  the  filter  is  displaced 
by  water  (usually  condensed  water) ;  when  the  gravity  of  this  wash 
water  falls  below  10°  Be.,  it  is  collected  in  a  special  tank  as  "  sweet 
water,"  *  until  the  gravity  falls  to  1°  or  2°  Be.  Then  boiling  water  is 

*  The  "  sweet  water  "  is  used  to  wash  the  bag  filters,  or  it  is  added  to  the  "  light 
liquors." 


STARCH,   DEXTRIN,   AND   GLUCOSE  369 

introduced  through  (F)  at  the  bottom  of  the  filter,  and  run  out 
through  (G)  at  the  top,  and  then  to  the  sewer,  as  long  as  any  matter 
can  be  washed  out  of  the  char. 

The  washed  char  is  drained,  and  then  "steamed  down"  by 
steam  from  (D)  to  displace  the  wash  waters.  It  is  then  shovelled 
out  through  the  lower  manhole  onto  the  conveyer,  and  carried  to  the 
kilns  where  it  is  revivified,  i.e.  its  decolorizing  power  is  restored.  It 
is  dried  by  passing  over  tubes  heated  by  waste  gases  from  the  fur- 
nace. The  dry  char  passes  automatically  into  narrow  vertical  retorts 
of  cast  iron  kept  at  a  full  red  heat.  The  lower  ends  of  these 
retorts  project  below  the  furnace,  and  end  in  sheet  iron  tubes  into 
which  the  hot  char  passes,  and  is  cooled  before  it  is  exposed  to  the 
air.  At  the  bottom  of  each  tube  is  a  valve  which  automatically 
discharges  a  certain  quantity  of  the  char  at  regular  intervals  onto  a 
belt  conveyer  running  below  the  kiln,  and  which  carries  the  revivi- 
fied char  to  revolving  reels,  where  it  is  sieved  to  remove  the  fine 
particles  before  returning  it  to  the  filter.  The  fine  char  ("spent 
black  ")  falling  through  the  sieve  is  of  no  further  use,  and  is  sold  to 
the  fertilizer  maker.  In  order  to  replace  this  constant  waste  as  fine 
dust,  about  200  pounds  of  new  char  is  run  into  the  filter  with  each 
charge.  Much  new  char  at  a  time  is  undesirable,  since  the  tarry 
matters  in  it  tend  to  color  the  syrup.  After  revivifying,  the  char  is 
boiled  one-half  an  hour  in  the  filter  with  hydrochloric  acid ;  then  it 
is  drained  through  (F),  and  the  acid  washed  away  with  condensed 
water.  The  char  is  now  ready  for  use.  The  life  of  the  char  in 
glucose  making  is  about  3  months  of  continuous  service,  and  during 
that  time  it  is  revivified  about  once  in  every  3  or  4  days. 

Glucose  is  not  so  freely  soluble  in  cold  water  as  is  cane  sugar, 
nor  is  it  so  sweet.  When  the  glucose  is  to  be  used  for  syrup,  some 
manufacturers  have  tried  to  increase  its  sweetening  power  by  add- 
ing a  small  quantity  of  saccharine,  an  intensely  sweet  organic  sub- 
stance. But  this  is  probably  not  practised  to  any  great  extent. 

Considerable  discussion  relative  to  the  healthfulness  of  glucose 
as  a  food  has  been  aroused  at  times ;  but  when  properly  made,  it  is 
improbable  that  it  is  in  any  way  injurious  to  health. 

Dextrose  belongs  to  that  class  of  sugars  which  are  capable  of 
fermentation,  with  the  formation  of  alcohol,  water,  and  carbon 
dioxide.  Because  of  this,  glucose  is  often  added  to  wine  and  beer 
wort  before  fermenting,  in  order  to  increase  the  percentage  of 
alcohol  in  the  beverage.  In  alkaline  solution,  glucose  has  a  very 
strong  reducing  action,  and  finds  some  use  in  the  arts  for  this  pur- 
pose ;  i.e.  for  the  reduction  of  indigo  to  the  soluble  form  known  as 

2B 


370  OUTLINES  OF  INDUSTRIAL   CHEMISTRY 

"  indigo  white,"  in  the  dye  vat.  It  is  also  extensively  used  in  the 
manufacture  of  confectionery,  jellies,  preserves,  medicines,  and  table 
syrups.  Being  a  thick,  heavy  liquid,  glucose  syrup  is  much  used 
as  a  thickening  agent  in  many  industries  and  to  give  body  to  many 
extracts  and  decoctions  in  pharmacy.  Since  it  is  a  neutral  sub- 
stance, odorless  and  colorless,  it  is  a  favorite  adulterant  for  thick 
liquids,  such  as  extracts  of  logwood,  tannins,  and  natural  dyewoods. 
Dextrose  can  be  made  from  cellulose  (C6H1005)rt,  the  conversion 
being  effected  in  the  same  way  as  when  starch  is  used;  but  it  is 
more  difficult  and  less  complete  with  dilute  acid.  It  is  thus  possible 
to  make  sugar  from  sawdust  or  old  cotton  rags  ;  but  it  is  not  now, 
and  probably  never  will  be  a  profitable  process. 

REFERENCES 

Die  Chemie  der  Kohlenhydrate.    R.  Sachsse,  Leipzig,  1877. 

Die  Starkefabrikation.     F.  Stohmann,  Berlin,  1879. 

Starch,  Glucose,  and  Dextrin.     Frankel  and  Hutter,  Philadelphia,  1881. 

Report  on  Glucose  by  the  National  Academy  of  Sciences  to  Commissioner  of 

Internal  Revenue.     Washington,  1884.     (Government  Printing  Office.) 
Die  Starkefabrikation,  Dextrin-  und  Traubenzucker-fabrikation.     L.  von  Wag- 

ner.   2te  Auf.     Braunschweig,  1886.     (Vieweg.) 
Die  Fabrikation  der  Starke,  des  Dextrins  u.s.w.    K.  Birnbaum,  Braunschweig, 

1887.     (Vieweg.) 

Handbuch  der  Kohlenhydrate.     B.  Tollens,  Breslau,  1888. 
Manual  of  Sugar  Chemistry.     J.  H.  Tucker.     3d  Ed.     New  York,  1890. 
Fabrication  de  la  Fecule  et  de  L'Amidon.     J.  Fritsch,  Paris,  1892  (?). 
Die  Starke-Fabrikation.     B.  von  Posanner,  Wien,  1894.     (Hartleben.) 
Die  Starke-Fabrikation  u.  die  Fabrikation  des  Traubenzuckers.     F.  Rehwald. 

3te  Auf.     Wien,  1895.     (Hartleben.) 
Zucker-  und  Starke-fabrikation.    Otto. 
Essai  des  Farines.     Cauvert. 
Die  Fabrikation  der  Kartoffelstarke.     O.  Saare,  Berlin,  1897.     (Springer.) 

CANE   SUGAR 


Sucrose  or  cane  sugar,  C^H^On,  is  found  in  many  plants,  but 
usually  in  association  with  other  substances  which  render  its  ex- 
traction difficult  and  unprofitable.  The  presence  of  dextrin,  glu- 
cose, "invert  sugars  "  (dextrose  and  Isevulose),  and  dissolved  mineral 
salts  in  any  considerable  quantity,  prevents  the  crystallization  of 
much  of  the  sucrose.  The  commercially  important  sources  of  sugar 
are  sugar  cane,  Saccharum  officinarum,  L.,  sugar  beet,  Beta  vulgar  is, 
L.,  sugar  maple,  Acer  saccharinum,  Wang.,  and  the  date  palm, 
Phoenix  dactylifera.  The  sorghum  plant,  Sorghum  vulgare,  Pers., 


CANE  SUGAR  371 

contains  considerable  sugar,  and  although  much  experimenting  has 
been  done,  owing  to  its  varying  content  of  sugar  and  its  large  per- 
centage of  gums  and  dextrin,  it  does  not  afford  a  satisfactorily 
crystallized  product.  Maple  sugar  is  only  of  special  value  for  its 
peculiar  flavor  as  a  crude  sugar.  If  refined,  it  loses  this  character- 
istic taste  and  is  not  distinguishable  from  ordinary  cane  sugar. 
Date  palm  sugar  is  produced  in  India  as  a  low  grade  crude  sugar ; 
it  is  known  as  "jaggary  "  and  is  shipped  for  refining. 

The  popular  term  "  sugar  "  was  originally  used  to  include  all 
substances  having  a  sweet  taste ;  hence  the  names,  cane  sugar,  fruit 
sugar,  sugar  of  lead,  etc.  But  now  the  name  is  restricted  to  sucrose 
as  obtained  from  cane  or  beets.  The  chemical  term  "  sugar  "  includes 
a  large  class  of  bodies  belonging  to  the  carbohydrates.  Sucrose  is 
a  crystallized  body,  soluble  in  one-half  its  weight  of  cold  water,  and 
in  much  less  hot  water.  Its  specific  gravity  is  1.593.  It  forms 
salts  called  sucrates,  with  certain  metallic  bases,  such  as  potassium, 
calcium,  barium,  and  strontium,  and  on  this  fact  depends  the  use 
of  lime,  baryta,  and  strontia  for  recovering  sugar  from  molasses. 
The  sucrose  derived  from  the  various  sources  is  identical  in  all 
cases,  though  the  raw  sugars  differ  somewhat  in  flavor  and  color, 
owing  to  the  nature  of  the  impurities  they  contain. 

The  sugar  cane  and  sugar  beet  supply  nearly  all  the  sucrose 
of  commerce.  The  former  grows  only  in  those  climates  which  are 
warm  and  moist,  with  intervals  of  .hot,  dry  weather;  the  most  of  the 
supply  comes  from  the  West  Indies,  the  Philippines,  Java,  the  Sand- 
wich Islands,  Brazil,  and  Louisiana.  Sugar  beets  thrive  best  in 
a  temperate  climate  and  are  extensively  raised  in  Germany  and 
France.  Extensive  experiments  in  raising  them  have  been  made 
in  this  country,  and  there  seems  to  be  110  obstacle  in  the  way  of 
climate  or  soil  to  their  cultivation ;  but  it  appears  that  under  the 
present  conditions  of  the  sugar  industry  there  is  more  profit  for  the 
farmer  in  other  crops. 

In  the  growing  plant,  the  only  sugar  present  is  glucose,  the 
sucrose  not  being  secreted  until  the  plant  reaches  maturity.  Anal- 
ysis of  the  ripe  cane  gives  the  following  average :  — 

Sugar 18.% 

Fibre 9.5 

Water 71. 

Analysis  of  the  ripe  cane  juice  shows :  — 

Water 80.% 

Sucrose 18. 

Glucose 0.30 

Gums  (Albuminoids) 1.40 

Mineral  Salts    .  .      0.30 


372 


OUTLINES   OF  INDUSTRIAL   CHEMISTRY 


But,  owing  to  the  imperfect  extraction  of  the  juice,  and  to  losses 
during  its  evaporation  and  clarification,  the  actual  yield  of  sugar 
is  much  less  than  the  analysis  would  indicate.  Usually  from  16 
to  20  per  cent  of  the  juice  is  left  in  the  "  begasse"  i.e.  the  waste 
cane  pulp. 

The  preparation  of  raw  sugar  from  sugar  cane  may  be  con- 
sidered under  four  heads :  (a)  extraction  of  the  juice;  (6)  clarifica- 
tion ;  (c)  evaporation ;  and  (d)  separation  of  the  crystals. 

(a)  Extraction.  —  The  cane  is  stripped  of  its  leaves  in  the  field 
and  taken  to  the  mill,  where  it  is  crushed  and  as  much  as  possible 


ifh       ifh 


of  the  juice  is  expressed.  This  must  be  done  very  soon  after  cut- 
ting, or  fermentation  begins  and  much  sugar  is  lost.  The  mills 
(see  Fig.  89)  consist  of  two  or  three  horizontal  rolls  from  30  to  60 
inches  in  diameter,  so  set  that  their  axes  are  parallel,  and  either 
at  the  vertices  of  an  isosceles  triangle  (as  in  the  figure),  or  in  the 
same  perpendicular.  The  rolls  are  set  in  adjustable  bearings. 
When  there  are  three  rolls,  the  cane  passes  between  the  top  roll 
(T)  and  first  bottom  roll  (B),  and  then  between  the  top  and  the 
second  bottom  roll  (D),  which  are  set  closer  together,  so  that  it  is 
crushed  twice.  It  is  usually  passed  through  two  or  three  mills,  and 
about  60  or  70  per  cent  of  the  juice  extracted.  It  is  customary  in 
Louisiana  to  use  shredder  machines.  These  consist  of  toothed 
wheels,  revolving  at  different  speeds,  which  cut  and  break  the  cane 
into  a  soft,  pulpy  mass  before  it  goes  to  the  mills.  This  increases 
the  yield  of  juice  to  a  little  over  75  per  cent  of  the  total  content  of 
the  canes.  The  crushed  cane,  coming  from  the  extraction  mills,  is 
generally  macerated  in  about  10  or  12  per  cent  of  cold  or  hot  water, 
to  which  a  little  milk  of  lime  has  been  added,  and  is  then  again 
passed  through  the  mill.  This  gives  an  additional  increase  of  2  or 


CAXE   SUGAR  373 

3  per  cent  in  the  yield  of  juice.  The  expressed  juice  is  caught  in 
a  trough  under  the  mill  and  is  run  off ;  the  begasse  or  "  trash "  is 
burned  under  the  boilers.  The  furnace  must  be  large  and  a  forced 
draught  is  used  to  keep  them  white  hot. 

Diffusion  methods  for  extracting  cane  juice,  similar  to  those  used 
for  sugar  beets  (p.  376),  but  at  a  temperature  of  90°  C.,  have  been 
tried,  but,  excepting  on  a  few  plantations  in  Louisiana,  with  no  great 
success,  since  the  refuse  needs  much  handling  and  drying  before  it 
can  be  burned,  and  an  abundant  supply  of  water  is  necessary. 

(6)  The  bits  of  cane  floating  in  the  juice  when  it  comes  from  the 
mills  are  removed  by  straining  through  wire  screens.  The  juice 
also  contains  organic  acids,  nitrogenous  bodies,  and  invert  sugar  in 
solution,  which  are  very  susceptible  to  fermentation.  To  remove 
these,  the  juice  is  defecated.  It  is  passed  through  a  heater,  placed 
in  the  vapor  pipe  of  the  vacuum  pan,  and  then  into  the  defecator 
tanks,  which  are  heated  by  a  steam  coil.  Here  milk  of  lime  is 
added  in  such  proportions  that  the  acids  are  almost  neutralized  and 
the  juice  left  very  slightly  acid  to  litmus.  The  lime,  aided  by  the 
heat,  coagulates  the  albumin  and  part  of  the  gummy  matters.  The 
liquid  is  rapidly  heated  to  boiling,  which  causes  the  coagulum  to 
rise  as  a  scum,  usually  about  2  inches  thick  and  consisting  of  lime 
salts,  holding  all  the  suspended  impurities  mechanically  entangled 
in  it.  After  standing  one-half  an  hour  or  an  hour,  the  scum  begins 
to  crack  and  is  skimmed  off;  or  the  juice  is  drawn  off  from  beneath 
it.  The  scum  is  run  into  scum  tanks,  where  it  is  mixed  with  more 
lime  and  with  sawdust  to  assist  in  the  subsequent  filter-pressing  by 
making  the  cake  more  porous.  The  filtrate  is  mixed  with  the  juice 
from  which  the  scum  is  decanted,  and  the  whole  is  then  ready  for 
evaporation. 

Calcium  acid  phosphate  is  sometimes  used  instead  of  lime  for 
defecation,  but  not  generally.  The  juice  contains  gummy  matter 
and  other  impurities,  which  interfere  with  the  crystallization  of  the 
sugar,  somewhat,  but  they  cannot  be  removed  entirely,  since  no 
cheap,  non-poisonous  material  is  known  that  will  coagulate  all  the 
gums.  Defecation  is  probably  the  most  important  step  in  sugar- 
making,  since  on  its  successful  working  depends  in  a  great  measure 
the  amount  and  quality  of  the  sugar  produced. 

(c)  The  process  of  evaporation  of  the  juice  has  been  greatly 
improved  in  recent  years  in  the  larger  sugar  houses.  By  the  old 
method  it  is  boiled  down  in  open  pans  until  the  mass  begins  to 
"grain,"  i.e.  to  crystallize,  and  then  it  is  emptied  into  shallow 
tanks  where  it  is  stirred  while  cooling.  The  mixture  of  crystallized 


374  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

sugar  and ^ molasses  is  then  filled  into  hogsheads;  holes  are  bored 
through  the  ends  of  the  casks,  which  are  then  placed  on  end,  in  a 
rack,  for  several  weeks,  and  the  molasses  allowed  to  drain  out  into 
a  receptacle  underneath.  The  holes  are  then  plugged  and  the  hogs- 
head of  sugar  is  sent  to  market.  The  best  grades  of  sugar  made  in 
this  way  are  called  muscovado;  they  are  light  brown  in  color  and 
contain  from  87  to  91  per  cent  of  sucrose.  This  process  is  now  but 
little  used,  and  only  in  the  less  progressive  countries.  Probably  no 
planter  can  derive  any  profit  from  muscovado  sugars  in  the  present 
state  of  the  industry ;  there  is  too  much  invert  sugar  produced, 
together  with  coloring  matter  formed  during  the  boiling.  Low 
grade  sugars  are  produced  in  this  way,  especially  the  jaggary 
sugars.  The  molasses  from  muscovado  sugar  was  formerly  used  as 
table  syrup,  and  some  is  still  so  used.  Concrete  sugars  are  made  by 
evaporating  the  juice  directly  to  a  hard  mass  in  a  special  pan  called 
a  "  concretor,"  no  attempt  being  made  to  separate  the  crystals  from 
the  molasses.  In  all  the  more  modern  sugar  houses,  the  juice  is 
evaporated  in  vacuum  pans.  It  is  generally  concentrated  in  a  triple 
effect  apparatus,  until  the  solution  contains  about  50  per  cent  solids, 
and  the  separation  of  crystals  is  about  to  begin.  It  is  then  trans- 
ferred to  a  simple  vacuum  pan,  called  the  "  strike  pan,"  where  the 
evaporation  is  continued  slowly  under  high  vacuum  ;  the  object  is  to 
build  up  the  crystals  on  the  crystal  points. 

(d)  When  the  grain  has  reached  the  desired  size,  the  mixture 
of  crystals  and  syrup,  which  is  called  "  masse-cuite"  is  emptied  into 
storage  tanks,  where  it  cools  somewhat.  It  is  then  run  into  cen- 
trifugal machines  which  separate  the  molasses  from  the  sugar.  The 
latter  is  called  the  "  first  sugar  "  and  is  at  once  packed  for  market. 
When  of  good  quality,  these  centrifugal  sugars  are  light  colored 
and  contain  95  to  97  per  cent  'pure  sugar.  Sometimes  the  juice  is 
treated  with  sulphur  dioxide  in  the  defecators,  and  the  sugar,  which 
is  then  nearly  white,  is  called  "  plantation  granulated." 

The  molasses  separated  from  the  first  sugar  is  called  first 
molasses  and  contains  45  to  50  per  cent  of  sucrose.  It  is  diluted 
and  defecated  with  lime  or  with  calcium  acid  phosphate,  and  the 
clarified  syrup  is  reboiled  in  the  vacuum  pans  to  obtain  a  "  second 
sugar."  This  is  slow  to  crystallize,  and  the  concentrated  syrup  is 
allowed  to  stand  from  3  to  7  days  in  a  room  kept  at  a  temperature 
of  60°  C.,  until  the  crystallization  is  complete.  The  mass  is  then 
" centriffed,"  yielding  a  "second"  or  "molasses"  sugar,  and 
'•second"  molasses.  This  sugar  is  of  variable  quality,  and  may 
be  sent  to  market  for  what  it  will  bring,  or  it  may  be  dissolved 


CANE   SUGAR 


375 


in  water  and  the  syrup  added  to  the  juice  going  to  the  vacuum 
pan. 

The  second  molasses  contains  about  40  per  cent  sugar,  which  it 
does  not  pay  to  recover.  It  is  sometimes  fermented  for  making 
rum  or  alcohol ;  or,  since  it  contains  a  high  percentage  of  carbona- 
ceous matter,  it  is  often  injected  into  the  furnace  in  a  fine  stream, 
where  it  has  a  certain  fuel  value.  A  small  amount  is  used  for  feed- 
ing cattle.  It  is  not  suitable  for  use  as  a  table  syrup  or  for  culinary 
purposes ;  but  a  small  amount  of  the  first  molasses  is  used  in  this  way. 

SYNOPSIS  OF   RAW   SUGAR   MAKING   FROM   SUGAR   CANE 

Cutting  and  Stripping  in  Cane  field 
(Shredders)  Mills 


36  to  40  per  cent  Begasse 
Furnaces 

i 
60  to  70  per  cent  Juice. 

1 
Defectors 

1 

1                                           -I 
Bag  Filters  or                                Scum 
Filter-presses                                     | 
Filter-press 

Press  Liquor               Press  Cake 

Multiple  Effect 
"  Strike  "  Vacuum  Pan 
Centrifugals 


First  Molasses 
(Defecators) 
Vacuum  Pans 


First  Sugar 


If 


iled  blank  "        If  "  boiled  to  grain 

Wagons  to  "  Hot  Room  " 
(3  to  7  days) 


Centrifugals 


Second  Molasses 

|  (Rum 

Used  for  \  Feeding  Cattle 
[Fuel 


Second  Sugar 


376  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

The  preparation  of  raw  sugar  from  beets  is  an  extensive  indus- 
try in  Europe.  It  consists  in  the  following  operations :  (a)  wash- 
ing and  slicing  the  beets ;  (b)  extracting  the  juice  ;  (c)  clarifying 
it ;  (d)  evaporating  it ;  (e)  separating  the  crystals ;  (/)  treating 
the  molasses. 

(a)  The   beets  are  washed  in  long  troughs,  each   containing  a 
revolving  shaft  which  carries   pins   set  in   the   form   of   a   screw. 
These   push  the  beets   along   against   a   stream   of   water   flowing 
through  the  trough,  and  by  rubbing  them  against  each  other,  loosens 
the  sand  and  loam,  which  are  carried  away  by  the  water.    The  beets 
are  then  cut  into  slices,  from  0.5  to  1  mm.  thick,  by  a  machine  con- 
taining revolving  knives. 

(b)  The  juice  is  now  usually  extracted  from  the  sliced  beets  by 
the  diffusion  process.     The  chips  are  put  into  vertical  iron  cylinders, 
and  systematically  digested  with  water  at  a  temperature  of  60°  C. 
The  digesters  are  arranged  in  batteries  of  ten,  and  between  each 
two  is  a  "  juice  warmer  "  or  "  calorisator,"  to  maintain  the  tempera- 
ture  of  the   apparatus.     These   are  similar  in  construction  to  the 
economizer  of  a  Feldmann's  apparatus,  and  consist  of  narrow  brass 
pipes  surrounded  by  a  steam  jacket.    When  the  chips  are  exhausted, 
they  are  removed,  the  digester  refilled  and  made  the  last  of  the 
series.     Fresh  water  is  admitted  to  the  tank  containing  the  most 
nearly  exhausted   chips,  and  passes  into  the  others  in  succession, 
finally  leaving  that  most  recently  filled,  as  a  sugar  solution  contain- 
ing nearly  as  much  sucrose  as  does  the  original  beet  sap ;  all  but 
0.5  per  cent  of  the  sugar  is  extracted.     About  150  parts  sugar  solu- 
tion are  obtained  for  every  100  parts,  by  weight,  of  beets.    The  spent 
chips  are  rich  in  nitrogenous    matter  and  are   often   pressed   and 
dried  for  cattle  food ;  or  they  are  returned  to  the  field  for  fertilizing. 

The  process  of  diffusion  depends  upon  osmosis.  When  the  vege- 
table cell  is  surrounded  by  water,  or  by  a  sugar  solution  of  less 
density  than  is  the  sap,  the  sugar  and  other  crystallizable  substances 
are  displaced  by  the  water  and  pass  through  the  cell  walls,  while  the 
colloid  bodies  (gums,  albuminoids,  etc.)  are,  for  the  most  part,  re- 
tained by  the  membrane.  Thus  the  juice  obtained  by  diffusion  is 
much  purer  than  that  obtained  by  other  means. 

Sometimes  the  beets  are  rasped  to  a  soft  pulp  in  machines  simi- 
lar to  those  used  in  making  starch  from  potatoes.  The  juice  isjhen 
expressed  in  hydraulic  presses  or  between  rolls. 

In  the  maceration  process  the  rasped  pulp  is  systematically  lixiv- 
iated with  water,  while  in  other  methods  centrifugal  machines  are 
used  to  extract  the  juice. 


CANE   SUGAR  377 

(c)  The  juice  is  clarified  in  much  the  same  way  as  is  that  from 
sugar  cane.     After  passing  through  a  sieve  to  remove  coarse  sus- 
pended impurities,  the  juice  is  defecated  with  lime  to  neutralize  the 
organic  acids  and  to  coagulate  the  albumin  and  mucus.     Any  excess 
of  lime  is  removed  by  forcing  carbon  dioxide  into  the  liquid  after 
the  neutralizing.     The  precipitate  of  calcium  carbonate  with  coagu- 
lated albumin,  etc.,  is  removed  by  filter-pressing.     The  clarified  juice 
is  then  treated  with  sulphur  dioxide  to  bleach  any  coloring  matter. 
Care  is  necessary,  in  both  these  saturation  processes,  to  leave  the 
juice  very  slightly  alkaline,  otherwise  inversion  of  the  sucrose  may 
be  caused. 

(d)  The  evaporation  of  the  clarified  juice  is  carried  on  in  two 
stages,  by  the  use  of  triple  effects  and  a  strike  pan,  much  in  the 
same  way  as  is  that  from  sugar  cane.     The  syrup  may  be  "  boiled  to 
grain,"  in  which  case  sugar  crystals  are  formed  in  the  strike  pan ;  or 
it  is  "  boiled  blank,"  by  which  a  clear,  thick  liquid  is    obtained, 
which  deposits  sugar  crystals  on  cooling.     The  first  method  is  gen- 
erally employed  and  gives  the  largest  yield  of  sugar;  but  a  very 
pure  syrup  is  required. 

If  the  syrup  froths  badly  during  evaporation,  a  small  amount  of 
butter  or  other  fat  is  introduced. 

(e)  The  mixture  of  molasses  and  sugar  is  separated  in  centrifugal 
machines  as  described  on  p.  374.     The  raw  sugar  so  obtained  is  very 
similar  to  the  first  sugar  from  cane. 

(/)  The  molasses  is  boiled  down  for  a  second  sugar  and  second 
molasses  as  already  described.  The  latter  contains  over  40  per  cent 
of  sugar  which  cannot  be  crystallized.  This  is  now  generally  re- 
covered by  treating  the  molasses  with  quicklime  or  strontium  hy- 
droxide in  excess.  A  tricalciumsucrate,  C12H220n  •  3  CaO,  is  formed, 
which  may  be  washed  with  alcohol  to  remove  the  non-sugar  sub- 
stances ;  or  it  may  be  separated  from  the  diluted  syrup  as  a  precipi- 
tate, and  filter-pressed,  leaving  the  impurities  in  solution.  It  is  then 
powdered  and  mixed  with  water  to  form  a  paste ;  this  is  either  used 
instead  of  lime  for  defecating  the  fresh  juice,  or  it  is  decomposed  by 
passing  carbon  dioxide  into  it.  In  either  case,  the  calcium  precipi- 
tates, leaving  the  sucrose  in  solution. 

In  the  strontium  process,  a  hot,  concentrated  solution  of  strontium 
hydroxide  is  added  to  the  molasses ;  on  cooling,  crystals  of  the  diffi- 
cultly soluble  mono-  or  di-strontium  sucrate  are  deposited.  These 
are  separated  by  filter-pressing  and  used  to  defecate  fresh  beet  juice ; 
or  they  may  be  decomposed  with  carbon  dioxide  to  remove  the  stron- 
tium and  set  the  sugar  free. 


378  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

Beet  sugar  molasses  contains  a  large  amount  of  potassium  salts, 
especially  sulphate,  which  prevent  the  crystallization  of  a  part  of  the 
sugar  content.  These  are  sometimes  removed  by  adding  aluminum 
sulphate,  thus  forming  an  alum  with  the  potash  salt.  The  alum  is 
then  eliminated  by  subjecting  the  molasses  to  dialysis,  the  potash 
salts  passing  through  the  membrane  and  the  sugar  remaining.  Beet 
sugar  molasses  also  contains  certain  nitrogenous  bodies  (amines?) 
which  impart  a  very  unpleasant  odor  and  taste,  rendering  it  unfit 
for  table  use.  But  it  is  nearly  free  from  invert  sugar  and  glucose, 
and  so  large  amounts  of  lime  may  be  used  in  defecating,  without 
injury  to  the  sugar.  When  heated  with  glucose,  lime  colors  the 
product  quite  deeply. 

In  this  country,  the  tariff  on  raw  sugar  is  adjusted  according  to 
its  color,  without  regard  to  the  actual  amount  of  sucrose.  Since 
some  of  the  better  grades  of  centrifugal  sugars  are  nearly  as  white 
as  the  refined  article,  the  law  is  sometimes  evaded  by  mixing  in  a 
small  quantity  of  the  deeply  colored  second  molasses.  The  color  is 
merely  on  the  surface  of  the  grain,  and  a  simple  washing  with  water 
or  dilute  syrup  in  a  centrifugal  machine  is  sufficient  to  remove  a 
large  part  of  it. 

SUGAR   REFINING 

Raw  sugar  derived  from  any  source  is  more  or  less  deeply  colored 
and  impure,  and  must  be  refined  to  yield  the  pure  white  sugar  for 
consumption.  It  would  seem  that,  on  economical  grounds,  the  refin- 
ing should  be  done  at  or  near  the  place  where  the  sugar  is  produced. 
But  at  present  the  refineries  are  not  in  the  same  countries  that  pro- 
duce the  raw  sugar ;  indeed,  they  exist  solely  to  remedy  the  errors 
and  careless  work  of  the  raw  sugar  maker,  or  to  circumvent  unfavor- 
able import  duties  levied  on  the  refined  sugar. 

Sugar  refining  is,  in  theory,  a  simpler  process  than  the  prepara- 
tion of  the  raw  sugar,  but  it  requires  great  care  and  attention  to  de- 
tail, as  well  as  much  expensive  machinery.  It  consists  in  dissolving 
the  crude  material,  separating  the  impurities,  and  recrystallizing  the 
sugar.  A  refinery  needs  a  frontage  on  navigable  water  and  ample 
dock  and  storage  sheds.  An  abundant  water  supply  for  condensers, 
for  washing  purposes,  for  melting  the  sugar  and  for  boiler  use,  is 
absolutely  necessary.  A  large  refinery,  capable  of  treating  900  tons 
of  sugar  per  day,  will  use  about  1,700,000  gallons  of  water  daily ;  of 
this,  about  1,000,000  gallons  is  used  in  the  condensers  of  the  vacuum 
pans.  The  next  largest  consumption  is  in  washing  the  char  filters. 

On  the  ground  floor  of  the  refinery  are  the  melting  tanks,  in  each 


CANE   SUGAR  379 

of  which  usually  16,000  pounds  of  sugar  can  be  dissolved,  to  form  a 
syrup  of  1.25  sp.  gr.  and  containing  55  per  cent  solids.  If  a 
centrifugal  *  or  artificially  colored  raw  sugar  is  to  be  used,  it  is  first 
dumped  into  elevators  which  carry  it  to  the  washing  plant.  There 
it  is  mixed  with  a  syrup  and  some  cold  water,  and  the  thick  magma 
passed  into  centrifugal  machines,  where  the  syrup,  carrying  most  of 
the  superficial  coloring  matter  and  some  of  the  glucose,  gums,  and 
dirt,  is  thrown  off.  This  leaves  the  raw  sugar  about  99  or  99J  per 
cent  pure ;  it  is  then  sent  to  the  melter.  The  syrup  goes  to  the 
melter  later,  and  is  mixed  with  a  lower  grade  of  sugar. 

The  melter  is  heated  by  closed  steam  coils,  contains  an  effi- 
cient stirring  apparatus,  or  mixer,  and  has  a  false  bottom,  to  retain 
coarse  impurities,  such  as  straw,  bits  of  cane,  leaves,  sticks,  and 
stones.  In  starting  the  day's  work,  it  is  customary  to  begin  with 
the  purest  sugar,  e.g.  the  centrifugal,  and  after  a  certain  amount  of 
this  has  been  dissolved  and  pumped  away,  to  melt  a  less  pure  sugar, 
e.g.  the  muscovado;  then  the  temperature  is  raised,  and  molasses 
and  poor  concrete  sugars  are  put  into  the  melter ;  next  come  the 
syrups  from  washing  the  raw  sugar,  together  with  various  syrups 
from  the  refining  process ;  these  are  followed  by  the  various  scums 
and  "  sweet  waters  "  (wash  waters)  of  the  refining. 

The  melter  is  filled  about  one-third  full  of  water  at  170°  F.,  the 
stirrer  put  in  motion,  and  the  first  charge  of  sugar  dumped  in ;  after 
15  minutes  it  is  dissolved,  and  the  liquor,  varying  in  color  from  a 
light  straw  color  to  dark  brown,  is  pumped  directly  to  the  "  blow- 
ups." 

The  blow-ups  are  defecators,  capable  of  holding  one  melt  (16,000 
pounds  of  sugar).  They  are  heated  by  closed  steam  coils,  and  each 
has  a  perforated  coil,  through  which  air  is  forced  to  agitate  the 
liquor.  The  temperature  is  kept  at  160°  F.  for  centrifugal  sugars, 
but  lower  grades  must  have  more  heat.  This  defecation  is  intended 
to  remove  the  gums,  organic  acids  and  impurities  (amines,  etc.),  and 
any  fine  suspended  dirt.  The  materials  used  are  lime,  alum,  clay, 
blood,  or  other  form  of  albumin,  soluble  phosphates,  and  often  fine 
bone-char.  Sugars  which  contain  but  little  glucose  will  bear  a  large 
quantity  of  lime,  without  risk  of  darkening  the  color.  Liquid  blood 
is  often  used,  about  4  gallons  being  necessary  for  each  blow-up. 
The  coagulated  blood  rises  to  the  top  as  a  scum,  entangling  the 
impurities,  which  are  thus  separated  from  the  liquor.  Soluble  cal- 
cium phosphate  (acid  phosphate)  is  now  much  used  instead  of  blood, 

*  Centrifugal  sugars,  as  distinguished  from  concrete  or  muscovado  sugars,  are 
those  from  which  the  molasses  has  been  separated  by  the  use  of  centrifugal  machines. 


380  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

the  amount  being  about  one-half  of  one  per  cent  of  the  weight  of  the 
sugar.  The  mixture  is  agitated  for  about  20  minutes,  and  then 
exactly  neutralized  with  lime,  when  a  flocculent  precipitate  separates, 
carrying  with  it  the  gums  and  suspended  matter. 

After  the  defecating  material  has  been  added,  the  temperature  is 
raised  to  212°  F.,  and  the  air  blast  turned  on  for  about  20  to  30  minutes. 
When  a  number  of  deep  cracks  appear  in  the  scum,  the  reaction  is 
ended,  and  the  liquor  is  drawn  off. 

From  the  blow-ups  the  defecated  liquor  passes  into  bag  niters, 
from  which  the  iiltrate  must  run  perfectly  clear,  or  the  sugar  will 
not  be  white.  The  bags  are  similar  to  those  described  on  page  11. 
They  are  suspended  in  a  closed  room,  about  12  by  6  by  8  feet,  fitted 
with  an  open  steam  coil,  by  which  the  bags  are  heated  to  180°  F.  be- 
fore the  liquor  is  allowed  to  run  into  them.  The  first  runnings  are 
muddy,  and  are  refiltered.  When  it  runs  clear,  the  liquor  is  col- 
lected in  tanks  placed  above  the  char-filters.  The  bags  finally  become 
clogged  with  mud,  which  is  very  slimy,  and  the  filtration  is  very  slow, 
but  is  usually  allowed  to  continue  for  about  twenty  hours.  Then  the 
bags  are  flushed  with  "  sweet  water,"  which  is  drawn  out  by  a  suction 
pipe,  and  returned  to  the  defecators.  The  bags  are  then  flushed  with 
hot  water,  until  the  liquor  draining  from  them  contains  only  2  per 
cent  of  solids.  They  are  then  turned  inside  out,  in  a  tank  of  hot 
water,  to  wash  off  the  soft  mud,  and  are  finally  thoroughly  washed 
with  clean  water  and  dried. 

The  mud  washed  from  the  bags  contains  about  20  per  cent  sugar, 
and  is  sent  to  special  tanks,  where,  after  further  dilution  with  water, 
lime  is  added  until  the  liquor  is  strongly  alkaline,  when  it  is  filter- 
pressed.  The  clear  syrup  from  the  filter-press  is  used  to  flush  the 
bag  filters  and  to  mix  with  the  melting  water  for  raw  sugar.  The 
mud  in  the  filter-press  is  washed  with  hot  water,  the  wash  waters, 
constituting  the  "  sweet  waters,"  being  used  for  diluting  and  flush- 
ing. The  mud,  still  containing  about  2  per  cent  of  sugar,  which  it 
does  not  pay  to  recover,  is  thrown  away. 

The  clear,  straw-colored  syrup  from  the  bag  filter  is  now  run  into 
the  char  filter.  These  are  very  similar  to  those  used  for  glucose  (Fig. 
88,  p.  368),  but  are  larger,  being  16  feet  deep  and  10  feet  in  diameter. 
The  bone-char  is  in  grains,  which  pass  a  No.  16  sieve,  but  remain  on 
a  No.  30  sieve.  Finer  grains  clog  the  filter,  and  coarser  ones  have 
less  action  on  the  coloring  matter  in  the  syrup.  The  char  is  washed 
with  hot  water  before  the  syrup  is  run  in,  but  it  is  not  "tempered" 
with  acid,  as  is  the  case  in  glucose  filtering.  About  1  pound  of  char 
is  used  for  each  pound  of  sugar  melted,  and  it  takes  6  hours  to  fill 


CANE   SUGAR  381 

the  filter  before  the  filtrate  begins  to  run.  After  revivifying,  the 
char  enters  the  filter  at  about  150°  F.,  and  the  liquor  is  filtered  at  the 
same  temperature.  After  some  time  the  filter  becomes  clogged,  and 
it  is  often  necessary  to  use  compressed  air  to  force  the  liquor  through 
the  char.  At  first  the  syrup  is  water  white,  but  later  it  becomes  col- 
ored, and  finally  the  char  is  "spent,"  and  must  be  revivified.  The 
char  is  washed  with  hot  water,  and  the  wash  waters  are  saved  until 
they  contain  only  2  per  cent  of  solids ;  below  this  they  are  thrown 
away.  This  cleansing  of  the  char  requires  about  20  hours.  It  is 
then  revivified,  as  described  on  page  369. 

The  filtered  syrup  then  goes  to  the  vacuum  pans,  which  are  of 
copper,  about  12  feet  high  and  10  feet  in  diameter,  a  "goose-neck" 
connecting  each  pan  with  the  condenser.  A  pan  full  of  syrup  is 
called  a  "skipping."  For  granulated  sugar,  the  syrup  is  run  in 
until  the  steam  coil  is  covered,  and  the  boiling  is  carried  on  at  160°  F., 
until  grains  appear;  then  more  syrup  is  added,  slowly,  and  the 
grains  grow  until  the  desired  size  is  reached.  Tests  are  taken  from 
time  to  time,  by  means  of  the  "proof  stick,"  a  solid  brass  rod  pass- 
ing through  a  stuffing  box  and  projecting  into  the  interior  of  the 
pan.  In  one  side  of  the  rod,  near  the  inner  end,  is  a  small  cavity, 
about  one-half  inch  deep.  When  the  rod  is  pulled  out  until  this 
cavity  is  outside  the  stuffing  box,  2  or  3  cubic  centimeters  of  syrup 
mixed  with  crystals  is  obtained.  Thus  small  samples  are  readily 
obtained  at  any  time,  without  interrupting  the  vacuum ;  and  from 
the  appearance  of  these  samples,  the  sugar-boiler  judges  of  the  prog- 
ress of  the  evaporation.  The  time  required  to  complete  the  process 
is  from  2  to  3  hours. 

When  the  grain  is  large  enough,  the  vacuum  pumps  are  stopped* 
and  air  is  slowly  admitted  to  the  pan.  The  bottom  valve  is  then 
opened,  and  the  magma  of  sugar  and  syrup  drops  into  coolers,  or 
mixers,  directly  beneath,  and  is  stirred  while  cooling,  to  prevent  the 
grains  agglomerating.  The  sugar  and  syrup  are  separated  in  cen- 
trifugal machines.  The  former  is  washed  in  the  centrifugal,  to 
remove  adhering  syrup,  and  is  then  dropped  into  a  storage  bin,  from 
which  it  is  carried  by  a  belt  conveyer  to  the  granulator.  This  is  a 
long,  rotating  cylinder  of  iron,  set  at  a  slight  incline,  and  heated  by 
steam.  By  passing  through  this  hot  tube,  the  sugar  is  thoroughly 
dried,  while  the  rotation  prevents  the  grains  sticking  together.  It 
then  passes  through  a  series  of  sieve  reels,  which  usually  separate 
the  grains  into  three  or  four  sizes,  the  commercial  sizes  being  packed 
in  barrels  for  market. 

The  syrup  from  the  centrifugals  is  reboiled  with  more  fresh 


382 


OUTLINES  OF  INDUSTRIAL   CHEMISTRY 


syrup,  or,  if  its  color  is  too  deep  for  this,  it  is  sent  back  to  the  char 
filter,  after  which  it  is  boiled  to  grain  for  soft  sugars,  the  tempera- 
ture in  the  vacuum  pan  being  110°  to  125°  F.  These  soft  sugars  are 
"centriffed,"  but  not  put  through  the  granulator,  and  are  boiled  to  a 
finer  grain  than  is  the  granulated.  In  many  cases  they  are  redis- 
solved  and  converted  into  granulated  sugars.  The  syrup  from  them 
is  amber  colored  or  brown,  and  is  barrelled  for  table  syrup  or  for 
manufacturing  purposes. 


SUGAR   REFINING 

Raw  Sugar  Warehouse 
Elevators 

Mixers 
Centrifugals 


Sugar                             Raw  s 
1 
Bins 

yrup 

Mel 

ters 

Blow 
Bagf 

-ups 
liters 

Scums  ("Mud") 

Washing  free  from 
sugar  liquor 

Removing  mud 
from  bags 


Syrup 
Heating  tanks 
Bone-black  ("Char")  Filters 


shii 


Mud  blow-ups      Washing  bags  for 
|  next  day's  use 

Filter-press 

I 


Dry  mud 


Thin  liquor, 
put  to  various 
uses. 


Washing  liquors    Vacuum  pans 
from  Char  | 
j Mixers 

Thin  liquor      Char  to 
Kilns 
Triple  effect  Centr  fugals 


Hea\ 

1 

ugar 

| 
ry  liquor      Syrup 

S 

1 

Returned  to      Reboiled 

Bins 

Char  filter       for  sugar 

Centrifugal 

Granulator 

l'  : 

Dryer 

Barrel  syrup        Soft 

I 
sugar 

Barrels 


CANE   SUGAR 


383 


The  loaf  sugar  of  commerce  is  made  by  running  the  magma  of 
syrup  and  fine  crystals  from  the  vacuum  pan  into  conical  moulds 
where  it  is  allowed  to  stand  for  some  time.  A  further  crystalliza- 
tion of  sugar  takes  place  which  cements  the  grains  together,  while 
the  uncrystallized  syrup  drains  off  through  a  small  hole  opened 
in  the  point  of  the  cone.  A  little  water  is  poured  on  the  surface  of 
the  sugar,  and,  percolating  down  through  the  mass,  displaces  any 
syrup  remaining.  This  draining  is  slow,  and  it  is  now  customary  to 
place  several  of  the  cones  in  a  centrifugal  machine,  with  their  points 
towards  the  outside  of  the  drum.  The  syrup  and  wash  waters  are 
forced  through  the  mass,  which  is  left  as  a  dry,  hard  conical  lump, 
the  "  sugar  loaf  "  of  trade. 


AVERAGE   ANALYSES   OF   SUGARS 


RAW  SUGAR. 

CANE 
SUGAR. 

GLUCOSE.* 

WATER. 

ORGANIC 
MATTER. 

ASH. 

Good  centrifugal  .     . 

96.5 

0.75 

1.50 

0.85 

0.40 

Poor  centrifugal    .     . 

92.0 

2.50 

3.00 

1.75 

0.75 

Good  muscovado  .     . 

91.0 

2.25 

5.00 

1.10 

0.65 

Poor  muscovado   . 

82.0 

7.00 

6.00 

3.50 

1.50 

Molasses  sugar      .     . 

85.0 

3.00 

5.00 

5.00 

2.00 

Jaggary  sugar  .     .     . 

75.0 

11.00 

8.00 

4.00 

2.00 

Manilla  sugar  .     .     . 

87.0 

5.50 

4.00 

2.25 

1.25 

Beet  sugar,  1st      .     . 

95.0 

0.00 

2.00 

1.75 

1.25 

Beet  sugar,  2d  .     .     . 

91.0 

0.25 

3.00 

3.25 

2.50 

REFINED  SUGAR. 

Granulated  sugar  .     . 

99.8 

0.20 

0.00 

0.00 

0.00 

White  coffee  sugar    . 

91.0 

2.40 

5.50 

0.80 

0.30 

Yellow  X  C  sugar 

87.0 

4.50 

6.00 

1.50 

1.00 

Yellow  sugar    .     .     . 

82.0 

7.50 

6.00 

2.50 

2.00 

Barrel  syrup    .     .     . 

40.0 

25.00 

20.00 

10.00 

5.00 

REFERENCES 

A  Treatise  on  the  Manufacture  of  Sugar  from  the  Sugar  Cane.    Peter  Soames, 

London,  1872.     (Spon  &  Co.) 

Guide  pratique  du  Fabricant  de  Sucre.     N.  Basset,  3  vols.,  Paris,  1875. 
Manuel  pratique  de  Diffusion.    Elie  Fleury  et  Ernst  Lemaire,  Paris,  1880. 
The  Sugar  Beet.     L.  S.  Ware,  Philadelphia,  1880.     (Baird  &  Co.) 
Manual  of  Sugar  Chemistry.     J.  H.  Tucker,  New  York,  1881. 
Die  Zuckerarten  und  ihre  Derivate.     E.  von  Lippmann,  Braunschweig,  1882. 

*The  term  "glucose"  includes  sugars  which  reduce  Fehling's  solution,  but  are 
not  necessarily  optically  active. 


384  OUTLINES   OF  INDUSTRIAL   CHEMISTRY 

Trait^  theorique  et  pratique  de  la  Fabrication  du  Sucre.     Paul  Horsin-De'on, 

Paris,  1882.     (Bernard  et  Cie.) 
Report  on  Sorghum  Sugar  by  a  Committee  of  the  National  Academy  of  Science, 

Washington,  1883. 
Lehrbuch  der  Zuckerfabrikation.     K.  Stammer.    2te  Auf.    Braunschweig,  1887. 

(Vieweg  u.  Sohn.) 

Handbuch  der  Kohlenhydrate.     B.  Tollens,  Breslau,  1888. 
Sugar.     A  Handbook  for  Planters  and  Refiners.     C.  G.  W.  Lock  and  B.  E.  R. 

Newlands  and  J.  A.  R.  Newlands,  London,  1888.     (Spon.) 
Die  Zuckerriibe.     H.  Briem,  Wien,  1889. 

Manuel  Pratique  du  Fabricant  de  Sucre.  P.  Boulin,  Paris,  1889. 
A  Guide  to  the  Literature  of  Sugar.  H.  L.  Roth,  London,  1890. 
Handbuch  der  Zuckerfabrikation.  3te  Auf.  F.  Stohmann,  Berlin,  1893.  (Paul 

Parey.) 

Introductory  Manual  for  Sugar  Growers.    F.  Watts,  London,  1893.     (Long- 
mans, Green  &  Co.) 

Die  Zuckerfabrikation.     B.  von  Posanner,  Wien,  1894. 

La  Sucre  et  1'Industrie  sucriere.  Paul  Horsm-De"on,  Paris,  1894.  (Bailliere  et  Fils.) 
Handbook   for    Sugar   Manufacturers    and   their   Chemists.      G.   L.    Spencer. 

3d  Ed.     New  York,  1897.     (Wiley  &  Sons.) 
Handbook  for  Chemists  of  Beet-sugar  houses  and  Seed-culture  Farms.     G.  L. 

Spencer,  New  York,  1897.     (Wiley  &  Sons.) 


FERMENTATION   INDUSTRIES 

Fermentation  is  a  general  term  applied  to  various  chemical 
changes  caused  by  the  action  of  certain  substances  called  ferments. 
These  are  of  two  classes:  (a)  Unorganized  chemical  substances, 
sometimes  called  enzymes,  and  including  such  bodies  as  diastase, 
invertase,  pepsin,  ptyalin,  emulsin,  etc.  Their  function  is  generally 
to  assist  in  the  assimilation  of  nutritive  material  by  the  animal  or 
plant  in  which  they  occur,  the  changes  which  they  cause  being  some- 
times of  the  nature  of  hydrolysis.  (6)  Organized  bodies  or  living 
organisms,  which  produce  very  complex  changes  in  the  substance 
upon  which  they  act,  probably  caused  in  part  by  the  enzymes 
secreted  by  them.  The  product  formed  varies  according  to  the  kind 
of  organism  predominating  in  the  liquid,  and  the  fermentation  is 
distinguished  as  alcoholic,  acetic,  lactic,  butyric,  etc.  Of  these,  the 
first  three  are  the  most  important. 

Organized  vegetable  ferments  may  be  divided  into  three  classes :  — 

(1)  Mould  growths. 

(2)  Yeast  plants,  or  Saccharomycetes. 

(3)  Bacteria,  or  Scliizomycetes. 

These  are  all  capable  of  growth  and  reproduction,  and  associated 
with  the  former  are  the  chemical  changes  called  fermentation  and 


FERMENTATION  INDUSTRIES  385 

putrefaction.  It  is  generally  true  that  alcoholic  fermentation  is 
caused  by  the  yeasts,  while  putrefactive  fermentation  is  due  to 
bacteria;  but  there  are  some  exceptions. 

Organized  ferments  may  be  reproduced  by  microscopic  spores, 
which  propagate  when  introduced  even  in  small  quantities  into  a 
fermentable  liquid,  and  cause  the  chemical  change  of  a  large  part  of 
it.  Consequently  these  spores,  floating  in  the  dust  in  the  air,  find 
their  way  into  fermenting  liquids  which,  when  freely  exposed  to  the 
air,  may,  therefore,  contain  many  kinds  of  ferments. 

The  moulds  are  thread-like  plants,  devoid  of  chlorophyl,  and 
forming  a  somewhat  felted  mass  called  the  mycelium.  They  grow 
readily  upon  fruit,  damp  wood,  wet  grain,  or  on  the  walls  of  damp 
cellars  and  similar  places,  forming  greenish,  bluish,  or  gray  vegeta- 
tions, which  emit  a  characteristic  musty  odor.  They  exert  an 
oxidizing  action  upon  organic  matter  and  hydrolyze  starch.  Since 
they  develop  musty  or  sour  odors  and  taste  in  the  nutrient  medium, 
destroy  sugars,  and  often  form  coloring  matter,  they  are  injurious  in 
fermenting  processes.  But  their  presence  is  mainly  due  to  negli- 
gence and  lack  of  cleanliness  and  proper  ventilation. 

The  bacteria,  splitting  ferments,  Schizomycetes,  are  microscopic 
plants  of  the  lowest  order,  forming  rods,  or  spiral,  thread-like,  or 
rounded  cells.  These  propagate  by  fission  with  astounding  rapidity, 
if  the  conditions  are  favorable ;  if  not,  some  forms  develop  spores, 
which  may  be  exposed  to  extreme  cold  or  to  moderately  high  tem- 
perature without  losing  their  power  of  germinating  when  brought 
into  a  proper  medium.  These  spores  are  scattered  everywhere,  in  the 
soil,  the  air,  and  water;  being  very  minute,  they  are  transported  by 
every  puff  of  wind,  and  thus  readily  find  access  to  liquids  and  moist 
substances  exposed  to  the  air.  For  their  nutriment  and  propagation 
they  need  about  the  same  substances  and  condition  of  temperature 
as  the  yeasts  (see  below).  They  cause  oxidation  and  decomposition, 
and  often  putrefaction,  in  many  bodies  containing  albuminous  and 
nitrogenous  material,  and  the  products  of  these  reactions  are  some- 
times extremely  poisonous.  Some  of  them  cause  acute  diseases  in 
man  and  in  animals.  Many  of  the  "  diseases  "  of  wine  and  beer,  as 
well  as  acetic,  lactic,  butyric,  and  other  fermentations,  are  caused  by 
them.  Also  the  production  of  nitrates  and  nitric  acid  in  the  soil 
(p.  121)  is  attributed  to  the  action  of  bacteria. 

Bacteria  are  much  more  susceptible  to  the  action  of  antiseptic 
substances  than  are  the  yeasts,  but  heat  and  cold  affect  them  less. 
Thus  the  process  of  Pasteurization  (p.  392)  is  not  a  sure  protection 
against  their  action. 
2c 


386  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

The  yeasts,  Saccharomycetes,  have  great  technical  importance, 
owing  to  the  part  they  take  in  alcoholic  fermentations.  Several 
species  are  recognized,  each  playing  some  particular  role  in  the  fer- 
mentation. Thus  Saccliaromyces  cerevisice  is  the  particular  ferment 
for  beer;  /S.  ellipsoideus  is  the  chief  organism  present  in  fermenting 
wine,  and  in  any  spontaneous  fermentation. 

Yeast  consists  of  an  aggregation  of  plant  cells,  forming  a  slimy, 
yellow  mass  of  peculiar  odor,  and  having  an  acid  reaction.  Under 
proper  conditions,  these  propagate  with  great  rapidity.  The  tem- 
perature must  be  constant  at  from  20°  to  30°  C.,*  and  substances 
necessary  for  the  growing  plant  must  be  present ;  these  are  a  fer- 
mentable sugar,  nitrogenous  matter,  and  certain  mineral  salts  such 
as  phosphates  and  sulphates  of  calcium,  potassium,  or  magnesium. 
Air  (oxygen)  is  necessary,  especially  at  first;  later  it  is  often  ex- 
cluded to  prevent  secondary  fermentations,  by  which  the  alcohol 
formed  is  converted  into  acetic,  butyric,  or  lactic  acid.  Through 
alcoholic  fermentation  the  fermentable  substance  in  the  liquor  is 
converted  into  alcohol  and  carbon  dioxide:  — 

C6H1206  =  2  C2H5OH  +  2  CO2. 

But  this  does  not  express  the  true  decomposition,  for  a  large  num- 
ber of  other  substances  are  formed  at  the  same  time,  the  more  im- 
portant being  glycerine,  succinic  acid,  butyl,  isobutyl,  and  amyl 
alcohols  (fusel  oil),  and  various  organic  ethers.  Owing  to  these  sec- 
ondary reactions,  the  yield  of  alcohol  is  somewhat  reduced. 

When  the  amount  of  alcohol  formed  in  the  liquid  equals  14  to  15 
per  cent,  the  yeast  can  no  longer  propagate  itself,  and  the  fermenta- 
tion ceases.  The  presence  of  certain  mineral  salts  such  as  borax, 
mercuric  chloride,  sulphurous  acid,  and  free  caustic  alkalies,  often 
retards  or  prevents  fermentation. 

The  fermentable  substance  in  the  liquid  to  be  fermented  with 
yeast  is  generally  a  sugar,  dextrose  being  the  most  readily  converted ; 
and  it  is  quite  possible  that  other  sugars  are  first  changed  to  glucose 
before  the  real  fermentation  begins.  For  example,  cane  sugar  is  not 
in  itself  readily  fermented,  but  by  the  action  of  the  invertase  secreted 
by  the  yeast,  it  is  converted  (hydrolyzed)  into  dextrose  and  laevulose, 
which  are  readily  fermented.  The  invertase  is  not  destroyed  in  this 
hydrolysis,  and  hence  there  is  scarcely  any  limit  to  the  amount  of 
cane  sugar  which  may  be  hydrolyzed  by  a  small  quantity  of  inver- 
tase. Maltose,  C^H^On,  is  also  readily  converted,  by  yeast,  into 
fermentable  dextrose,  and  thence  into  alcohol  and  carbon  dioxide; 

*  A  higher  temperature  is  conducive  to  the  formation  of  fusel  oil. 


FERMENTATION  INDUSTRIES  387 

or,  perhaps  the  maltose  is  fermented  directly,  without  the  interme- 
diate formation  of  dextrose.  Starch  is  not  capable  of  direct  alcoholic 
fermentation,  but  must  first  be  converted  into  fermentable  sugar. 
This  conversion  is  easily  accomplished  by  the  action  of  diastase, 
which  changes  the  starch  into  maltose. 

Yeasts  are  also  grouped  in  two  general  classes,  viz. :  top  yeasts 
and  bottom  yeasts.  The  former  require  rather  high  temperature  (15° 
to  30°  C.)  for  the  fermentation,  which  is  very  active,  the  rapid  evo- 
lution of  carbon  dioxide  causing  the  liquid  to  bubble  violently,  and 
carrying  the  yeast  to  the  surface.  This  yeast  is  used  for  heavy  ales 
and  beer,  for  alcohol  and  high  wines,  and  for  some  wine.  Bottom 
yeast  acts  at  a  lower  temperature  (4°  to  10°  C.),  and  the  fermentation 
is  slow;  the  evolution  of  carbon  dioxide  is  gradual,  and  the  yeast 
remains  on  the  bottom  of  the  vat. 

The  researches  of  Pasteur,  Reess,  Hansen,  and  others,  have  thrown 
much  light  on  the  nature  and  properties  of  the  yeasts.  Hansen 
divides  the  Saccharomyces  into  six  typical  species,  as  follows :  — 

Saccharomyces  cerevisice,  —  the  beer  ferment  most  commonly  em^ 
ployed  in  breweries.  It  may  be  a  top  yeast,  i.e.  floating  on  the  sur- 
face of  the  fermenting  liquid,  or  a  bottom  yeast,  according  to  the 
conditions  existing  during  the  fermentation. 

Saccharomyces  Pastorianus  I.,  —  a  beer  ferment  which  causes  an 
unpleasant  bitter  taste  in  beer.  It  is  a  bottom  yeast,  remaining  on 
the  bottom  of  the  vat  during  the  fermentation. 

Saccharomyces  Pastorianus  II.,  —  a  top  yeast  found  in  beer,  but 
which  appears  to  have  no  action  upon  it. 

Saccharomyces  Pastorianus  III.,  —  a  beer  ferment  causing  cloudi- 
ness and  disease  in  the  beer..  It  is  a  top  yeast,  resembling  the  last  two. 

Saccharomyces  ellipsoideus  /.,  —  a  bottom  yeast,  the  true  wine  fer- 
ment. It  occurs  on  the  grapes. 

Saccharomyces  ellipsoideus  II.,  —  a  yeast  causing  the  cloudiness  in 
turbid  beer.  It  is  a  bottom  yeast,  and  resembles  the  last  mentioned 
above. 

In  addition  to  the  above,  Hansen  also  isolated  from  a  brewer's 
yeast  two  varieties,  known  as  Carlsberg  Nos.  1  and  2,  and  closely 
resembling  S.  cerevisice.  No.  1  yields  a  beer  with  less  carbon  diox- 
ide than  No.  2,  and  is  mainly  employed  for  bottle  beers ;  No.  2  is 
used  for  export  beers. 

All  these  yeasts  ferment  glucose,  sucrose  after  inversion,  and 
maltose,  but  not  lactose.  Other  yeasts  are  known  which  ferment 
sucrose,  but  not  maltose,  and  still  others  which  contain  no  invertase, 
and  will  not  ferment  sucrose. 


388  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

For  technical  purposes,  it  has  long  been  the  custom  to  use  culti- 
vated yeasts  for  alcoholic  fermentation;  but  Pasteur  showed  that 
these  contain  many  "wild  yeasts,"  i.e.  plants  whose  nature  and  ac- 
tions were  either  unknown,  or  are  detrimental  to  the  product.  Han- 
sen  reasoned  from  his  observations  on  the  effect  produced  by  the 
eight  above  described  yeasts,  that  for  a  uniform  quality  of  product 
there  must  be  exactly  the  same  kind,  or  kinds,  of  yeast  employed  in 
each  brew.  Hence  he  devised  his  system  of  pure  yeast  cultures, 
obtained  in  sterilized  nutrient  material  by  propagation  from  a  single 
plant.  Thus  a  single  variety  of  yeast  is  obtained,  by  the  use  of 
which  the  fermentation  is  more  easily  controlled. 

In  fermentations  at  a  high  temperature,  where  the  amount  of 
alcohol  formed  is  near  the  maximum,  the  yeast  plant  generally  dies ; 
but  by  low  temperature  fermentation  the  propagation  of  the  plant 
is  so  rapid  that  a  large  excess  is  formed  over  the  amount  needed  for 
the  next  lot  of  liquor  to  be  fermented.  Hence  the  brewer  has  yeast 
to  sell,  and  at  the  same  time  is  enabled  to  preserve  the  variety  un- 
changed through  a  considerable  period  of  time. 

There  are  three  purposes  for  which  the  alcoholic  fermentation  is 
carried  on  technically :  (a)  for  the  manufacture  of  the  yeast ;  (6)  for 
the  carbon  dioxide  formed ;  (c)  for  the  alcohol. 

The  first  of  these  is  usually  associated  with  the  third,  and  con- 
sists in  growing  a  pure  yeast  free  from  wild  yeast  and  other  fer- 
ments. The  process  of  growth  is  carefully  watched  by  the  aid  of 
the  microscope,  and  the  appearance  of  any  injurious  variety  con- 
demns the  whole  lot. 

Those  most  generally  cultivated  are  the  S.  cerevisice  and  S.  ellip- 
soideus.  The  cells  are  filtered  out  of  the  liquid  in  which  they  are 
grown,  by  fine  sieves,  usually  of  bolting  cloth,  and  are  washed  with 
cold  water,  filter-pressed,  and  the  cake  heavily  pressed.  It  is  then 
mixed  with  from  25  to  50  per  cent  of  starch  or  flour  and  brought 
into  market  as  "  compressed  yeast."  By  drying  at  a  low  tempera- 
ture the  plant  retains  its  vitality  for  the  most  part,  and  will  grow 
when  put  into  a  fermentable  solution. 

The  liquid  from  which  the  yeast  cells  have  been  filtered  is  some- 
times allowed  to  ferment  further  until  the  action  ceases ;  it  is  then 
distilled  for  alcohol.  The  yeasts  are  grown  in  a  filtered  extract  of 
malt,  and  since  they  require  free  access  of  oxygen  for  their  greatest 
development,  it  is  now  customary  to  force  a  blast  of  sterilized  air 
through  the  fermenting  liquid.  This  hastens  the  process  and  in- 
creases the  yield  of  yeast,  but  decreases  the  formation  of  alcohol  so 
that  its  recovery  is  unprofitable. 


FERMENTATION   INDUSTRIES  389 

At  a  low  temperature,  compressed  yeast  will  keep  for  a  long  time ; 
but  in  warm,  moist  air  it  rapidly  decomposes  or  develops  mould 
growths.  Dried  yeast  is  less  active  than  the  compressed,  but  will 
bear  exposure  to  the  air  and  can  be  kept  for  a  longer  period.  The 
chief  use  of  commercial  yeast  is  for  bread  making. 

Fermentation  for  the  carbon  dioxide  is  practically  confined  to  the 
manufacture  of  bread.  In  this  a  mixture  of  flour  and  water  is 
allowed  to  ferment.  The  nitrogenous  matter  in  the  flour  furnishes 
nutriment,  and  the  starch  is  partly  converted  into  fermentable  sugar 
by  the  ferments  always  present  in  the  flour  and  yeast.  A  vigorous 
alcoholic  fermentation  begins,  liberating  a  considerable  volume  of 
carbon  dioxide,  which,  being  retained  by  the  pasty  dough,  causes  the 
whole  mass  to  swell  and  become  porous.  When  bread  dough  is 
baked,  the  heat  kills  the  yeast,  stopping  all  fermentation,  and  at  the 
same  time  evaporates  off  the  alcohol,  and  finally  it  hardens  the 
gluten,  dextrin,  and  starch  paste,  retaining  the  porous  structure  in 
the  mass. 

Fermentation  for  the  alcohol  is  a  very  extensive  industry.  This 
may  take  place  without  the  addition  of  prepared  yeast,  as  in  the  case 
of  most  wines ;  but  the  germs  of  the  ferment  are  then  derived  from 
the  air  or  are  present  upon  the  skins  of  the  fruit,  and  so  when  the 
latter  is  crushed  they  are  mixed  with  the  juice.  In  all  cases,  how- 
ever, where  starch  is  to  be  converted  into  alcohol,  malt  and  yeast 
are  employed. 

"WINE 

Wine  is  fruit  juice  which  has  undergone  an  alcoholic  fermenta- 
tion ;  it  is  most  commonly  made  from  grapes.  The  fermentation  is 
spontaneous  and  progresses  without  special  attention  until  the  sugar 
has  been  converted  to  alcohol.  The  fermentable  sugars  in  grape 
juice  are  dextrose,  Isevulose,  and  some  inosite ;  when  fully  ripe  it 
contains  on  an  average  18  per  cent  of  fruit  sugar,  in  addition  to 
tartaric  acid  (as  potassium  bitartrate),  malic  acid,  a  little  butyric 
acid,  albuminoids,  non-nitrogenous  matter,  and  ash.  All  these  vary 
in  quantity  according  to  the  kind  of  grape  and  the  nature  of  the  soil 
and  climate.  The  grape  skins  contain  tannin  (C14H1009),  oils,  and 
(except  in  white  grapes)  coloring  matter  (oenocyanin).  These  all 
pass  into  the  juice  when  the  grape  is  pressed. 

The  character  of  the  soil  in  which  the  vine  grows  influences  the 
fruit  very  materially.  It  must  be  light  and  porous,  and  contain  salts 
of  potassium,  lime,  magnesium,  iron,  and  sodium,  especially  sul- 
phates, phosphates,  chlorides,  and  silicates.  Decomposed  volcanic 


390  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

rock,  such  as  granite  and  lava,  appear  to  furnish  the  best  soil.  A 
warm  summer  with  only  a  moderate  amount  of  rain  is  essential  for 
a  high  percentage  of  sugar  in  the  juice,  and  the  highest  percentage 
is  usually  obtained  in  October  in  latitude  near  40°.  If  the  grapes 
are  allowed  to  hang  until  overripe,  the  amount  of  sugar  decreases 
somewhat,  but  the  wine  sometimes  has  a  peculiar  bouquet  which  is 
much  prized. 

When  ripe,  the  grapes  are  carefully  picked  and  sometimes  sorted 
into  several  grades.  For  the  finest  wines  they  are  removed  from  the 
stems,  since  these  contain  an  excess  of  tannin  and  tartaric  acid. 
They  are  crushed  between  wooden  rolls  or  by  pounding  in  mortars, 
or  by  treading  with  the  bare  feet.  The  juice  is  extracted  by  press- 
ing, or  better  in  centrifugal  machines.  It  is  called  "  must "  and  con- 
tains the  soluble  matter  of  the  grape.  The  quality  of  the  wine  de- 
pends in  a  great  measure  on  the  ratio  of  the  sugar  to  the  free  acids 
(tartaric  and  malic).  The  most  favorable  ratio  is  1  part  of  acid  to 
29  parts  of  sugar,  but  the  average  is  about  1  to  16. 

For  red  wines  it  is  customary  to  allow  a  partial  fermentation  of 
the  mash  before  pressing  out  the  juice.  The  alcohol  thus  formed 
extracts  the  coloring,  matter  from  the  skins  more  thoroughly  than  it 
can  be  directly  expressed.  White  wine  is  made  from  white  grapes. 

Through  the  action  of  the  wine  ferment,  Saccharomyces  ellipsoideus, 
present  on  the  grape  and  in  the  air  of  grape-producing  regions,  fer- 
mentation begins  in  the  must  at  once.  It  takes  place  in  two  stages  : 
the  active  fermentation,  which  lasts  from  one  to  three  weeks ;  and  the 
still  fermentation,  continuing  for  several  months.  The  former  takes 
place  in  open  vats  or  tubs  at  a  moderate  temperature  (10°  to  30°  C.). 
It  may  be  a  "  bottom  fermentation,"  where  the  temperature  is  from 
10°  to  15°  C.,  or  a  "  top  fermentation  "  at  20°  C.  or  above.  The  former 
is  generally  practised  in  Northern  Europe  and  produces  wines  low  in 
alcohol  but  having  a  fine  aroma  or  "bouquet."  Top  fermentation, 
which  is  more  rapid,  seldom  lasting  more  than  a  week,  is  carried  on 
in  Southern  Europe,  and  yields  wine  high  in  alcohol  but  lacking 
bouquet. 

In  a  few  hours  after  being  put  into  the  fermenting  vats  the 
clear  must  becomes  turbid  and  acquires  a  sour  taste  and  smell ;  soon 
a  rapid  evolution  of  carbon  dioxide  begins  and  a  froth  forms  on  the 
surface.  Some  manufacturers  expose  the  must  freely  to  the  air  and 
stir  it  frequently  to  aerate  it,  but  others  exclude  the  air  as  much  as 
possible.  A  moderate  amount  of  aeration,  especially  at  first,  is 
doubtless  beneficial ;  but  towards  the  end  of  the  active  fermentation 
too  much  air  admission  may  introduce  the  acetic  ferment,  Bacterium 


FERMENTATION  INDUSTRIES  391 

aceti.  During  this  fermentation  the  albuminoids  are  largely  con- 
sumed by  the  growing  yeast.  Finally  the  active  fermentation  be- 
comes slow  and  the  must  is  now  known  as  "  new  wine."  It  is  drawn 
into  closed  tubs  or  casks  which  are  filled  quite  full  and  the  opening 
loosely  closed  to  prevent  the  access  of  the  acetic  ferment.  Here  the 
still  fermentation  takes  place,  the  time  depending  largely  upon  the 
temperature  of  the  fermenting  cellar;  the  lower  the  temperature, 
the  less  rapid  the  fermentation.  The  yeast  settles,  and  as  the  alco- 
hol content  increases,  a  crystallization  of  acid  potassium  tartrate, 
together  with  some  calcium  salts  and  coloring  matter,  takes  place, 
forming  as  a  deposit  called  argol ;  this  is  the  source  of  the  "  cream 
of  tartar  "  of'commerce. 

When  it  has  become  clear,  and  nearly  the  whole  of  its  sugar  con- 
tent has  been  converted  into  alcohol,  the  wine  is  drawn  off  into  large 
casks.  The  bungs  are  closed  and  the  wine  allowed  to  "  ripen  "  for 
perhaps  two  or  three  years.  During  this  process,  which  is  essentially 
an  oxidation,  the  albuminoids  and  tannins  are  largely  precipitated, 
together  with  some  of  the  coloring  matters  and  other  impurities. 
At  the  same  time  the  higher  alcohols  or  fusel  oil  formed  during  the 
fermentation  combine  with  the  free  acids  present  to  form  organic 
ethers  which  impart  the  peculiar  flavors  to  wines.  In  order  to 
hasten  the  ripening  process,  the  wine  is  frequently  drawn  off  from 
the  casks  and  a  little  gelatine,  isinglass,  milk,  blood,  or  albumin 
added  each  time.  This  forms  a  precipitate  which  drags  down  the 
fine  suspended  matter.  Gelatinous  silicic  acid,  kaolin,  gypsum,  or 
plaster  of  Paris  are  also  used  for  this  clarifying.  The  last  two,  how- 
ever, react  with  the  tartrate  of  potassium  always  present  in  the  wine, 
forming  potassium  sulphate  and  precipitating  calcium  tartrate.  The 
former  remains  in  the  wine,  and  since  it  has  an  injurious  action  on 
the  human  system,  the  use  of  plaster  and  gypsum  is  prohibited  in 
some  countries.  When  the  ripening  process  is  complete,  the  wine  is 
bottled  and  is  ready  for  consumption. 

The  use  of  pure  cultures  of  yeast  for  the  fermentation  of  wine 
has  recently  been  introduced  with  good  results,  yielding  products 
which  ripen  more  readily  and  have  good  keeping  qualities. 

Wine  is  subject  to  various  "  diseases  "  due  to  bacteria  and  other 
ferments.  Sourness  is  caused  by  an  acetic  fermentation  due  to  too 
much  exposure  to  the  air.  Kopiness  is  the  result  of  mucus  fermen- 
tation. Stale  or  flat  taste  and  bitterness  are  produced  by  a  peculiar 
fungus  or  plant  growth.  These  troubles  may  be  prevented  by  care 
in  handling  the  wine,  attention  to  cleanliness,  and  by  always  keep- 
ing the  casks  full  to  prevent  the  entrance  of  air.  Any  shrinkage 


392  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

through,  evaporation  or  leakage  should  be  replaced  with  more  wine 
at  once.  Those  diseases  which  are  caused  by  ferments  can  usually 
be  remedied  in  the  early  stages  by  heating  the  wine  to  about  70°  C., 
which  kills  most  of  the  injurious  germs  and  renders  the  wine  capa- 
ble of  long  keeping  and  transportation.  This  process,  called  Pasteur- 
izing, does  not  injure  the  aroma  and  other  qualities.  It  is  carried 
out  by  immersing  the  bottled  wine  in  hot  water,  or  by  running  the 
wine  from  the  cask  through  long  pipes  placed  in  tanks  of  hot  water. 

Other  methods  of  improving  the  keeping  qualities  of  wine  are  the 
addition  of  salicylic  or  boric  acid,  but  these  are  considered  injurious 
to  health  and  are  prohibited  in  some  European  countries.  A  very 
general  practice  is  to  fume  the  casks  with  sulphur  dioxide  and  to 
wash  them  with  sodium  bisulphite  solution  before  filling  with  wine. 
Sometimes  sulphurous  acid  is  added  to  the  wine  to  act  as  a  preserv- 
ative. 

Wine  made  from  grape  juice  as  it  is  expressed  from  the  fruit  is 
rarely  found  in  market.  The  juice  varies  from  year  to  year  accord- 
ing to  the  amount  of  rain,  sunshine,  average  temperature,  fertiliza- 
tion and  other  causes ;  thus  the  proportion  of  sugar,  tannin,  acid, 
etc.,  changes,  and  the  wines  vary  somewhat  on  fermentation.  For 
this  reason,  must  or  new  wine  is  "  improved."  A  common  method 
is  to  mix  in  the  juice  of  other  kinds  of  grapes  or  to  add  new  wine  of 
different  character.  If  the  must  is  too  high  in  sugar  and  low  in 
acid,  a  sour  wine  is  added  until  the  desired  ratio  is  obtained.  If 
already  too  sour,  it  is  "  Gallized "  by  adding  water  and  sugar,  or 
"  Chaptalized "  by  neutralizing  the  excess  of  acid  with  marble  dust 
or  precipitated  calcium  carbonate.  To  make  a  sweet  wine,  a  con- 
siderable amount  of  cane  sugar  is  added. 

These  modifications  are  restricted  by  legal  enactment  in  most 
European  countries,  and  the  addition  of  large  quantities  of  alcohol, 
glucose,  and  glycerine  (Seheeleizing)  is  generally  prohibited.  But 
in  the  case  of  certain  heavy  Spanish  and  Portuguese  wines,  such  as 
Port  and  Madeira,  the  addition  of  rectified  alcohol  is  recognized  as 
legitimate.  But  such  substances  as  logwood,  cochineal,  kermes,  or 
other  natural  or  coal-tar  coloring  matters,  are  always  considered 
adulterants. 

Much  inferior  wine  is  made  by  leaching  the  pulp  ("  marc  ")  from 
the  wine-press  with  water,  adding  sugar,  and  fermenting  the  ex- 
tract. This  gives  a  cheap  wine,  much  used  by  the  poorer  people  of 
France  and  other  European  countries.  But  it  must  not  be  sold  as 
a  natural  wine. 

Considerable  artificial  wine  is  made  by  mixing  water,  alcohol, 


FERMENTATION  INDUSTRIES  393 

sugar,  glycerine,  tartaric  acid,  tannin,  fruit  essences,  etc.,  to  produce 
a  liquor  resembling  the  natural  product.  Within  a  few  years  an 
industry  has  been  established  in  France  for  the  manufacture  of 
wine  from  raisins  and  prunes.  These  are  macerated  in  a  mixture 
of  water,  brandy,  sugar,  tartaric  and  tannic  acids,  and  the  whole 
fermented  with  yeast.  The  product  is  colored  if  desired. 

Champagne  is  made  from  certain  sweet  white  wines.  The  must 
is  pressed  from  the  grape  as  soon  as  possible  after  picking,  and  then 
fermented.  The  new  wine  is  clarified  with  isinglass  and  "im- 
proved" very  carefully  by  mixing  with  other  wines.  A  certain 
amount  of  cane  sugar,  mixed  with  Cognac  is  then  added  and  the 
wine  bottled  (the  best  corks,  which  have  been  soaked  in  wine,  are 
used)  and  placed  in  a  room  warmed  to  24°  C.  A  fermentation  takes 
place  in  the  bottle  and  the  wine  becomes  highly  charged  with  car- 
bon dioxide.  The  amount  of  sugar  added  is  calculated  to  liberate 
enough  of  this  gas  to  cause  a  pressure  of  about  five  atmospheres  in 
the  bottle.*  The  bottles  are  placed  on  the  side  and  left  for  some 
months;  then  they  are  turned  with  the  cork  down,  until  the  sedi- 
ment collects  just  above  it.  The  cork  is  then  carefully  removed  for 
an  instant,  until  the  sediment  has  blown  out.  The  loss  is  replaced 
with  liqueur  (a  solution  of  cane  sugar  and  aromatic  essences  in  the 
best  Cognac),  the  cork  is  replaced  and  wired  in,  and  the  label  put  on 
the  bottle.  It  is  then  ready  for  market. 

An  imitation  champagne  is  now  largely  made  by  forcing  carbon 
dioxide  into  a  sweet,  white  wine,  *to  which  some  liqueur  has  been 
added. 


Besides  grape  wines,  other  fermented  fruit  juices  are  used  as 
beverages.  Of  these,  the  commonest  in  this  country  are  hard  cider 
and  currant  wine.  These  do  not  keep  well  unless  sugar  has  been 
added  before  fermenting. 

Palm  wine  is  made  in  tropical  countries  from  the  sap  of  the 
palm. 

Pulke  is  a  drink  prepared  in  Mexico  from  the  juice  of  certain 
cactus  plants. 

Kumis  is  a  wine-like  drink  made  from  the  fermented  milk  of 
cows,  mares,  or  goats.  The  milk  sugar  is  converted  into  lactic  acid, 
alcohol,  and  carbon  dioxide.  It  is  chiefly  made  by  the  inhabitants 
of  the  Russian  steppes. 

*  From  5  to  8  per  cent  of  the  bottles  burst. 


394  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 


BREWING 

Brewing  involves  alcoholic  fermentation,  but  it  differs  from  wine 
making  in  that  it  is  always  started  by  the  addition  of  yeast  to  the 
liquid  to  be  fermented.  Spontaneous  fermentation  is  not  desired, 
and  precautions  are  taken  to  prevent  it. 

Beer  is  a  fermented  alcoholic  drink  intended  for  consumption 
during  the  after  fermentation,  while  still  charged  with  carbon 
dioxide.  It  is  made  from  sprouted  grain  (malt),  starchy  materials, 
and  hops.  The  malt  is  generally  barley,  as  this  yields  the  largest 
percentage  of  diastase  and  affords  the  richest,  best  flavored  beer.* 
The  starchy  material  is  derived  from  unmalted  corn,  rice,  or  other 
grain. 

The  quality  of  the  water  used  for  brewing  is  very  important  as 
affecting  the  product.  In  general,  the  water  should  be  moderately 
hard  and  the  salts  desired  in  it  are  calcium  and  magnesium  sul- 
phates and  sodium  chloride.  If  very  much  iron  is  present,  the 
water  should  be  purified ;  very  soft  water  is  improved  by  the  addi- 
tion of  gypsum.  Water  containing  much  organic  matter  in  solution, 
or  an  unduly  large  number  of  bacteria,  should  not  be  used. 

The  processs  of  brewing  may  be  divided  into  malting,  mashing 
(including  the  boiling  and  cooling  of  the  wort),  fermentation,  and 
bottling  or  barrelling. 

Malting  is  now  very  generally  done  by  separate  concerns,  except 
in  only  the  largest  breweries.  *  The  process  consists  in  cleaning, 
softening,  sprouting,  and  drying  the  grain.  During  the  sprouting, 
two  ferments,  diastase  and  peptase  are  formed,  while  the  cell  walls 
enclosing  the  starch  are  softened  and  disintegrated  so  that  the  inte- 
rior of  the  kernel  becomes  "  mealy,"  thus  facilitating  the  transforma- 
tion of  the  starch  into  sugar.  The  production  of  diastase  is  the 
chief  aim  of  the  maltster.  The  secretion  of  this  ferment  increases 
as  the  germination  proceeds,  until  it  reaches  a  maximum,  after 
which  it  decreases  if  the  germination  is  not  stopped.  The  amount 
of  diastase  is  estimated  by  the  length  of  the  sprout  or  acrospire,  and 
is  greatest  when  this  has  extended  about  three-fourths  of  the  length 
of  the  grain.  The  appearance  and  length  of  the  rootlets  also  serves 
as  a  guide  to  the  experienced  maltster. 

The  mode  of  the  formation  of  the  diastase  is  not  yet  known, 
It  is  a  nitrogenous  body,  easily  soluble  in  cold  water  and  possessing 
the  power  to  convert  very  large  quantities  of  starch  into  maltose, 

*  Wheat,  corn,  and  other  grains  are  occasionally  malted  for  certain  kinds  of 
beer. 


FERMENTATION   INDUSTRIES  395 

C^HaOu,  and  dextrin.  Since  good  malt  contains  a  great  excess  of 
diastase  over  the  amount  needed  to  convert  its  own  starch  into 
sugar,  mixtures  of  raw  grain  and  malt  are  allowed  to  react  until  the 
starch  of  the  former  is  converted  into  sugar,  and  then  the  whole  is 
fermented. 

The  dust,  dirt,  dead  and  broken  kernels,  and  foreign  seeds  are 
first  removed  by  careful  sieving  in  revolving  sieves,  the  dust  and 
chaff  being  blown  away  by  a  strong  blast  of  air. 

The  grain  is  then  "  steeped  "  by  soaking  it  for  two  or  three  days 
in  water  at  12°  C.,  in  wood-lined  tanks  or  cemented  cisterns.  It  is 
stirred  frequently,  and  the  dead  kernels  float  and  are  removed.  The 
water  extracts  much  soluble  matter,  oil,  etc.,  from  the  grain,  and  is 
changed  as  it  becomes  colored. 

The  grain  increases  about  20  or  25  per  cent  in  volume  and  about 
50  per  cent  in  weight,  and  when  a  test  of  a  few  kernels  shows  that 
they  are  so  soft  that  the  skin  may  be  readily  removed,  the  grain  is 
couched  by  piling  in  a  nicely  levelled  heap  about  20  to  24  inches 
deep,  on  the  malting  floor,  which  is  made  of  cement  and  is  kept  very 
clean.  The  room  is  usually  only  moderately  lighted,  and  the  air  is 
kept  moist  by  frequently  sprinkling  the  grain  and  floor  with  water ; 
a  good  circulation  of  air  in  the  room  to  supply  plenty  of  oxygen  to 
the  grain  is  a  prime  essential.  Great  care  is  taken  to  keep  the  tem- 
perature even,  at  about  15°  to  16°  C.  Higher  temperature  tends  to 
cause  mould  growth  and  excessive  root  development.  After  a  few 
hours  the  temperature  begins  to  rise  within  the  couch,  and,  as  the 
grain  heats,  it  becomes  moist  on  the  surface  ("sweats  ")  and  evolves 
an  agreeable  odor.  The  germination  has  begun,  and  very  soon  the 
rootlets  appear.  The  time  of  couching  is  from  20  to  30  hours,  accord- 
ing to  the  temperature  and  time  of  steeping. 

The  grain  is  then  floored  by  spreading  it  with  wooden  shovels  on 
the  floor,  in  an  even  layer  about  10  inches  deep.  To  prevent  its 
heating  too  rapidly,  it  is  turned  over  every  5  or  6  hours,  thus  bring- 
ing new  grain  to  the  top ;  each  succeeding  day  the  layer  is  spread 
thinner,  until  it  is  finally  only  4  inches  deep ;  the  grain  is  sprinkled 
from  time  to  time  to  keep  it  moist.  The  germination  is  rapid 
and  must  be  carefully  watched;  after  from  6  to  12  days,  when 
the  acrospire  has  reached  the  desired  length,  the  growth  is  stopped 
by  spreading  it  in  thinner  layers ;  the  moisture  evaporates  and 
the  germ  withers.  The  " green  malt"  is  then  transferred  to  the 
drying  room,  which  usually  has  two  floors,  made  of  wire  gauze  or 
perforated  iron  plates.  The  malt  is  spread  on  the  upper  floor  and 
dried  at  a  temperature  of  38°  to  50°  C.  To  produce  kiln-dried  malt, 


396  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

it  is  transferred  to  the  lower  floor,  where  it  is  much  hotter,  and  is 
dried  at  100°  C. ;  sometimes  it  is  even  partially  charred.  The  air  in 
the  drying  room  may  be  heated  by  fire  gases  passing  through  pipes 
under  the  gratings,  or  by  an  open  fire  in  the  lower  part  of  the 
room;  in  this  latter  case  the  products  of  combustion  pass  through 
the  malt,  imparting  -a  darker  color  and  a  peculiar  taste  to  it  and 
to  the  beer  made  from  it.  The  character  and  color  of  the  beer  are 
much  influenced  by  the  mode  of  drying  the  malt.  The  higher  the 
temperature,  the  more  diastase  is  destroyed  and  the  less  soluble  the 
protein  is  rendered.  After  drying,  the  rootlets  are  brittle  and  are 
easily  removed  by  passing  the  malt  through  cylindrical  sieves  con- 
taining rotary  brushes. 

The  production  of  a  malt  uniform  in  its  properties  throughout  by 
the  above  method  is  very  difficult,  while  different  lots  are  sure  to 
vary  a  good  deal,  according  to  the  temperature  and  humidity  of  the 
air.  Consequently,  at  certain  seasons  of  the  year,  it  was  customary 
to  suspend  operations.  Pneumatic  malting  has  been  recently  intro- 
duced, and  as  it  remedies  the  above  difficulties,  prevents  mould  and 
acidity,  is  easily  controlled,  and  requires  less  labor  and  less  floor 
space,  it  has  replaced  the  old  system  in  all  large  malt  houses.  Two 
forms  of  pneumatic  malting  have  been  devised. 

The  Galland  process  consists  in  placing  the  softened  grain  in  a 
rotating  drum  (Fig.  90),  containing  along  its  inner  circumference 
several  channels  (A,  A),  covered  with  wire  gauze  and  opening  into 
the  chamber  (C)  at  the  end  of  the  drum.  A  tube  (B)  of  wire  gauze 
extends  along  the  centre  of  the  drum  and  connects  with  an  outlet 
pipe  (E).  Into  the  chamber  (C)  a  pipe  (D)  opens,  which  contains  a 
valve  that  makes  connection  with  the  flue  (F),  or  with  the  pipe  (G), 
as  desired.  Air  is  drawn  through  coke  towers,  kept  at  a  constant 
temperature  of  about  14°  C.,  and  through  which  water  trickles.  The 
air  then  passes  down  the  flue  (H),  where  it  is  in  contact  with  a  fine 
spray  of  water  escaping  under  pressure  from  the  supply  pipe  (J).  It 
is  thus  cooled,  or  warmed,  as  necessary  to  the  constant  temperature 
of  14°  C.,  and,  laden  with  moisture>  passes  through  (F)  and  (D)  into 
the  chamber  (C),  and  thence  into  the  drum,  through  the  channels 
(A,  A).  The  drum  is  filled  about  two-thirds  full  with  the  swollen 
grain ;  and  as  it  rotates  about  once  in  40  to  50  minutes,  there  is  a 
slow  turning  over  of  the  whole  mass  of  the  grain.  The  air,  entering 
through  (A,  A),  passes  through  the  mass,  and  enters  the  inner  tube 
(B),  from  which  it  passes  to  (E),  and  thence  to  the  exhauster,  which 
drives  it  out  of  the  building.  Thus  the  grain  is  kept  at  a  constant 
temperature  in  a  moist  atmosphere,  with  a  very  effective  circulation 


FERMENTATION  INDUSTRIES 


397 


of  air,  and  a  constant  change  of  surface  of  the  kernels,  which  pre- 
vents undue  heating.  The  grain  sprouts  as  on  the  malting  floor,  but 
there  is  no  handling  and  consequent  breaking  and  crushing  of  the 
kernel,  and  no  opportunity  for  the  development  of  mould ;  since  the 
air  is  filtered,  very  few  germs  are  introduced.  When  the  germina- 
tion has  gone  as  far  as  is  desired,  the  valve  in  (D)  is  changed  to  cut 
off  the  moist  air,  and  connection  is  made  with  (G),  from  which  warm, 
dry  air  is  drawn  into  the  drum,  rapidly  drying  the  acros-pire  and 
rootlets.  The  drums  hold  from  1J  to  5  tons  of  barley  at  a  charge, 
and  the  time  necessary  for  the  process  is  about  8  days. 


FIG.  90. 

By  the  Saladin  system,  the  softened  barley  is  placed  in  a  long 
tank,  having  a  false  bottom  of  gauze,  and  provided  with  a  mechan- 
ical stirring  apparatus,  travelling  from  one  end  of  the  tank  to  the 
other  on  a  movable  carriage.  This  stirrer  hangs  down  into  the 
grain,  and  mixes  it  effectively  without  crushing  any  kernels.  Moist 
air  enters  under  the  false  bottom,  and  passing  through  the  wet  grain, 
escapes  into  the  room,  and  is  drawn  away  by  an  exhauster.  When 
the  sprouting  is  ended,  warm,  dry  air  is  drawn  through  the  malty  as 
above  described. 


Mashing  consists  in  converting  the  starch  in  the  mixture  of  grain 
and  malt  into  maltose  and  dextrin,  through  the  action  of  the  dias- 
tase in  the  malt,  and  at  the  same  time  extracting,  the  soluble  carbo- 


398  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

hydrates  and  nitrogenous  bodies.  The  peptase,  going  into  solution, 
is  supposed  to  convert  part  of  the  albuminoids  into  peptones  and 
amides,  which  are  readily  soluble  in  water,  and  constitute  a  part  of 
the  "  extract "  present  in  the  finished  beer.  Some  of  these  bodies, 
however,  if  present  in  a  large  amount,  may  cause  cloudiness  in  the 
product,  as  they  are  precipitated  from  cold  solution  by  alcohol.  It 
is  generally  supposed  that  by  drying  the  malt  at  a  high  temperature 
these  protein  substances  are  rendered  less  soluble  in  the  mash 
liquor,  and  being  thus  filtered  out,  the  beer  is  clear  and  bright.  The 
use  of  unmalted  grain,  especially  corn  or  rice,  in  mashing,  is  also 
advocated,  *  on  the  ground  that  it  contains  no  protein  matter  to 
cloud  the  beer.  But  the  real  nature  and  value  of  peptones  in  the 
mash  liquor  is  not  yet  definitely  settled. 

The  most  favorable  temperature  for  the  action  of  the  diastase  is 
from  60°  to  65°  C.,  at  which  point  it  rapidly  hydrolyzes  the  starch, 
and  converts  it  into  maltose  and  numerous  dextrins,  —  amylodex- 
trin,  erythrodextrin,  and  archodextrin  probably  being  intermediate 
products.  About  one-fourth  of  the  starch  is  usually  left  in  the  form 
of  dextrin. 

According  to  Ost,  the  large  starch  molecule  decomposes  into  sev- 
eral smaller  dextrin  molecules  :  — 

mn  (C^HaoOio)  =  n  (mC12H2o010). 

Of  these  dextrins,  some  combine  with  water  to  form  maltodextrin, 
an  intermediate  product  between  dextrin  and  maltose,  which  fer- 
ments very  quickly  with  top  yeast.  These  dextrins  are  further 
converted  into  maltose  by  the  diastase :  — 

mCuHaAo  +  mH20  =  m  (C12H220,i). 

A  complete  conversion  of  the  starch  into  maltose  is  not  desired 
for  beer,  since  the  presence  of  the  unfermentable  dextrin  imparts 
fulness  of  body  and  nutritive  properties,  which  are  increased  by  the 
albuminoids,  peptones,  and  amides.  These  also  keep  up  a  slow  fer- 
mentation after  the  beer  has  been  drawn  into  casks  or  bottles.  It  is 
often  customary,  therefore,  to  limit  the  diastatic  action  by  kiln-dry- 
ing the  malt  at  a  high  temperature,  or  by  mashing  with  very  hot 
water  at  first,  or  by  rapidly  heating  a  part  of  the  mash  to  boiling. 

There  are  two  general  processes  of  mashing :  the  infusion  method, 
generally  practised  in  the  United  States  and  in  England ;  and  the 
decoction  method,  usually  employed  in  Europe.  By  the  former  pro- 
cess the  dry  malt  is  crushed  between  rolls  so  that  the  hull  bursts,  but 

*  Robert  Wahl,  Indian  Corn  in  the  Manufacture  of  Beer,  U.  S.  Dep't  Agricul- 
ture, Washington,  1893. 


FERMENTATION  INDUSTRIES  399 

it  is  not  ground.  It  then  passes  into  a  large  "  mash-tub,"  provided 
with  a  cover  and  an  effective  stirring  apparatus.  English  brewers 
mix  the  malt  directly  with  hot  water  at  75°  C.,  as  it  saves  time  and 
labor,  and  the  extraction  of  the  malt  seeing  to  be  more  complete. 
But  this  hot  water  destroys  much  of  the/diastase,  and  prevents  the 
complete  action  of  the  peptase  on  tire  albuminoids,  thus  leaving 
them  in  the  beer,  where  they  sometimes  cause  cloudiness. 

American  brewers  usually  mix  the  malt  with  a  little  water  at 
50°  to  60°  C.,  and  the  temperature  is  kept  there  for  some  time,  as 
this  is  the  most  favorable  temperature  for  the  diastase  and  peptones 
to  do  their  work.  Then  the  mash  is  slowly  heated  to  70°  C.,  by 
running  in  boiling  water  or  free  steam.  By  this  slow  heating  the 
starch  is  all  converted  by  the  diastase  before  it  is  hot  enough  to 
form  a  paste.  Some  brewers  prefer  to  start  with  cold  water  in  the 
mash-tub,  and  heat  slowly  to  70°. 

The  raw  cereal  used  in  the  mash  is  generally  ground  and  mixed 
with  a  small  quantity  of  the  malt  in  a  special  tub;  then  water  at 
about  38°  C.  is  run  in,  and  after  about  30  minutes  the  temperature  is 
raised  to  60°  C.,  where  it  remains  another  half-hour,  the  stirrer 
being  in  constant  operation.  Then  the  mixture  is  heated  to  boiling 
for  an  hour,  and  finally  the  softened  raw  grain  is  run  into  the  mash- 
tub,  where  the  rest  of  the  malt  has  been  wet  with  water  at  38°  C., 
and  the  mashing  process  proceeds  as  above. 

Mashing  usually  takes  an  hour  or  more,  and  the  stirrer  is  kept  in 
constant  operation.  The  product  is  a  liquid  called  "  wort,"  contain- 
ing maltose,  isomaltose,  dextrins,  peptones,  and  amides. 

The  decoction  process  yields  a  more  concentrated  wort,  and  is 
generally  used  where  fuel  is  expensive,  and  when  a  full  bodied, 
highly  extractive  beer  is  desired.  The  crushed  malt  is  mixed  with 
twice  its  volume  of  cold  water  in  the  mash-tub,  and  then  the  full 
amount  of  water  desired  is  made  up  by  adding  boiling  water,  thus 
raising  the  temperature  of  the  mash  to  38°  C.  About  one-third  of 
the  whole  mash  is  then  pumped  into  the  decoction  pan  (a  boiler 
heated  either  by  free  fire  or  by  steam,  and  having  a  good  stirrer), 
where  it  is  rapidly  heated  to  boiling,  and  at  once  run  back  into 
the  mash-tub,  where  the  stirrer  is  working  actively.  This  raises 
the  temperature  of  the  mash  to  about  50°  C.  Again  one-third  of  the 
contents  of  the  mash-tub  is  heated  to  boiling  in  the  decoction  pan, 
and  run  back,  heating  the  mash  to  62°  C.  Another  repetition  of 
this  process  raises  the  temperature  to  70°  to  72°  C.,  when  the  mash 
is  allowed  to  stand  quietly  for  30  minutes. 

The  wort  obtained  by  either  process  is  filtered  from  the  husks  of 


400  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

the  malt,  and  other  solid  residue.  When  the  infusion  process  is 
used,  the  mash-tub  generally  has  a  false  bottom  of  perforated  copper 
plate,  the  holes  being  sufficiently  fine  to  retain  the  residue.  When 
the  stirrer  is  stopped,  this  insoluble  matter  settles  to  the  bottom, 
and  collecting  on  the  grating,  forms  a  filtering  layer  which  retains 
the  suspended  matter,  while  the  wort  is  drawn  off  below  the  false 
bottom.  The  first  runnings  are  turbid,  and  are  refiltered.  In  the 
decoction  process,  it  is  customary  to  run  the  mash  into  a  special  tub 
for  this  filtration.  In  order  to  remove  all  the  wort  from  the  residue, 
a  washer  called  a  " sparger"  is  used.  This  is  merely  a  large 
Barker's  mill  with  arms  extending  to  within  half  an  inch  of  the 
sides  of  the  mash-tub,  and  with  a  row  of  holes  one-twentieth  of  an 
inch  in  diameter,  and  two  inches  apart,  extending  along  the  back  of 
each  arm.  The  flow  of  water  causes  the  arms  to  rotate,  and  it  is 
evenly  distributed.  The  process  is  continued  with  hot  water  (75°  C.) 
until  the  washings  reach  a  density  of  1°  Tw. 

The  filtered  wort  is  next  run  into  the  brewing  kettle  or  copper, 
where  it  is  boiled  for  some  time.  This  has  several  objects  :  — 

(a)  It  concentrates  the  wort,  which,  by  the  infusion  process 
especially,  is  very  dilute,  and  about  one-fourth  of  the  water  must 
be  evaporated. 

(6)  It  destroys  the  diastase,  peptase,  and  any  other  ferment 
which  may  be  present,  and  thoroughly  sterilizes  the  wort. 

(c)  It  coagulates  and  precipitates  most  of  the  albuminous  matter 
remaining  in  the  wort. 

(d)  It  affords  an  opportunity  of  adding  the  hops,  which   are 
boiled  with  the  wort  from  one-half  an  hour  to  an  hour. 

Hops  are  the  female  flowers  (catkins)  of  Humulus  Lupulus,  L. 
The  leaflets  contain  tannin,  while  the  yellow  powder  (lupulin,  hop 
meal,  or  hop  flour),  attached  to  the  surface  of  the  catkin,  contains 
hop  oil,  certain  alkaloids  or  bitter  principles,  and  resins.  The  oil  is 
volatile,  and  is  present  to  the  extent  of  0.25  to  0.30  per  cent.  It 
imparts  the  bitter  flavor  to  the  beer.  If  boiled  too  long,  part  of  this 
oil  is  lost.  The  alkaloids  are  supposed  to  give  the  narcotic  char- 
acter to  hops.  The  resins  contain  most  of  the  antiseptic  principles, 
which  are  protective  against  the  lactic  ferment,  and,  to  a  less  degree, 
against  the  acetic  ferment ;  hence  more  hops  are  added  to  lager  beer 
which  is  stored  several  months  before  going  to  market,  than  to  that 
intended  for  immediate  consumption.  About  one  pound  of  hops  to 
100  gallons  of  wort  is  the  lowest  limit,  while  as  much  as  12  pounds 
per  100  gallons  are  used  for  some  of  the  heavy  English  ales  and 
porters. 


FERMENTATION  INDUSTRIES  401 

The  best  varieties  of  hops  are  raised  in  Bohemia  and  Bavaria, 
but  they  are  also  largely  cultivated  in  other  parts  of  Germany,  in 
France,  and  in  the  United  States. 

After  boiling  the  wort  from  one  to  six  hours,  according  to  the 
character  of  the  wort,  and  of  the  beer  desired,  the  hop  catkins  are 
removed  by  straining  the  wort  through  sieves  in  a  vessel  called  the 
"  hop-back.'7  They  are  then  washed,  and  sometimes  pressed,  to 
obtain  all  the  extractive  matter. 

The  hot  wort  is  then  pumped  through  a  rose  or  sprayer  into  a 
receiving  tank  placed  in  a  well-ventilated  room.  It  falls  for  some 
distance  as  a  fine  mist,  and  is  aerated  and  cooled  some  25°  to  30°. 
It  stands  in  this  tank  until  a  sediment  deposits.  The  wort  is  still 
hot,  and  is  drawn  off  and  rapidly  cooled*  to  the  temperature  of 
fermentation  by  running  over  the  Baudelot  cooler,  or  "  beer-fall."  t 
This  consists  of  a  series  of  horizontal  copper  pipes,  about  two  and 
one-half  inches  in  diameter,  placed,  one  above  the  other,  to  a  height 
of  ten  or  twelve  feet,  and  through  which  cold  water  or  ammonia 
circulates ;  the  wort,  running  over  the  surface  of  the  pipes  in  thin 
films,  is  quickly  cooled  to  the  temperature  of  the  water.  Sometimes 
the  flow  of  wort  is  inside  the  pipes,  and  the  water  passes  over  the 
outside  of  the  beer-fall. 

From  the  cooler,  the  wort  passes  to  a  tank,  where  it  is  allowed  to 
settle,  and  the  clear  liquid  is  then  drawn  into  the  fermentation 
butts.  These  are  made  of  oak,  and  lined  with  pitch  or  asphaltum, 
and  hold  from  1500  to  3000  gallons.  They  are  set  in  underground 
cellars  or,  more  commonly  now,  in  rooms  cooled  to  a  constant  tem- 
perature by  refrigerating  machines;  or  water,  cooled  to  the  tem- 
perature of  fermentation,  flows  through  a  coil  of  copper  pipe  placed 
in  the  butt.  A  certain  amount  of  pure  yeast  is  added  to  each  tub, 
the  process  being  called  "pitching,"  and  within  a  few  hours  the 
active  fermentation  begins.  In  some  breweries  it  is  now  the  practice 
to  add  the  yeast  in  the  settling  tanks ;  after  a  few  hours  the  wort  is 
drawn  from  above  the  sediment  (consisting  of  coagulated  albuminous 
matter,  dead  yeast  cells,  hops,  and  other  solid  impurities),  and  passes 
into  the  fermentation  butts,  carrying  with  it  enough  young  yeast  cells 
to  cause  active  fermentation.  According  as  the  temperature  of  the 

*  Lactic  or  acetic  fermentation,  which  would  sour  the  beer,  is  apt  to  take  place 
during  the  cooling.  To  prevent  infection  of  the  wort  by  bacteria  and  wild  yeasts, 
systems  for  ventilating  the  cooling  rooms  with  filtered  or  sterilized  air  are  often  used. 

t  This  apparatus  has  generally  replaced  the  old  style,  shallow  cooling  pans  in 
which  the  wort  was  exposed  to  the  air  in  a  broad  layer  only  a  few  inches  deep. 

2D 


402  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

wort  is  low  (5°  to  8°  C.)  or  high  (15°  to  18°  C.)  there  is  a  "  bottom  "  or 
a  "top  fermentation."  The  former  is  used  for  lager  beers,  and  the 
latter  for  ale,  porter,  and  stout. 

In  the  bottom  fermentation  the  active  fermentation  does  not 
begin  for  12  to  18  hours  after  pitching.  Then  a  scum  appears  on 
the  wort,  and  is  blown  into  a  foam  by  the  escaping  carbon  dioxide. 
After  three  or  four  days  this  foam  rises  to  the  top.  or  even  several 
inches  above  the  top  of  the  butt,  while  its  surface  is  broken  by  deep 
cracks.  The  carbon  dioxide  escapes  over  the  sides  of  the  butt,  and 
falling  to  the  floor  is  usually  carried  away  by  an  artificial  draught.* 
Finally  the  surface  of  the  foam  shows  a  brown  color,  and  in  six  or 
seven  days  the  active  fermentation  diminishes,  the  temperature  falls, 
and  the  yeast  settles  to  the  bottom.  After  ten  days  the  active 
fermentation  ceases  entirely,  and  the  new  beer  is  drawn  into  storage 
vats,  carrying  with  it  some  yeast,  which  sets  up  an  after  fermenta- 
tion; the  maltose  remaining  is  slowly  decomposed,  and  substances 
are  formed  which  improve  the  flavor.  These  casks  are  of  oak,  coated 
with  pitch  inside,  and  usually  holding  about  1500  gallons.  The 
temperature  during  this  period  is  kept  low,  and  air  is  given  free 
access  to  the  liquor.  The  yeast  grows  thriftily,  and  consumes  more 
of  the  albumins,  so  that  lager  beers  are  lower  in  these,  and  are  more 
stable  than  top  fermentation  beers.  The  time  of  this  storage  varies 
from  three  to  six  months.  To  assist  in  clarifying  it,  the  beer  is 
usually  drawn  into  "  chip  casks,"  in  which  are  shavings  of  beech 
wood  which  have  been  well  cleaned  by  boiling  with  sodium  carbon- 
ate. For  the  same  purpose,  isinglass  dissolved  in  pyroligneous  or 
sulphurous  acid  is  usually  added  in  the  chip  casks,  together  with 

*  The  amount  of  carbon  dioxide  formed  is  said  to  be  about  equal  to  the  weight 
of  the  alcohol.  Methods  have  recently  been  devised  to  save  this  gas  for  use  in 
refrigerating  machines,  or  for  carbonating  the  finished  beer.  It  is  evolved  rapidly 
and  regularly  for  some  time,  and  is  collected  in  a  hood  let  down  over  the  fermenta- 
tion vat  to  within  a  few  inches  of  the  surface  of  the  liquid.  The  level  of  the  gas  is 
gauged  by  means  of  a  toy  rubber  balloon,  filled  with  air,  which  floats  on  the  surface 
of  the  gas.  The  carbon  dioxide  is  carefully  pumped  from  the  hood  so  that  no  air  is 
drawn  with  it.  It  is  then  purified  by  passing  through  water,  and  then  through  a 
solution  of  potassium  permanganate,  and  finally  through  concentrated  sulphuric 
acid.  It  is  compressed  at  about  60  atmospheres,  and  then  passed  through  cooling 
coils  for  condensation.  The  compressed  gas  is  said  to  be  about  99  per  cent  pure,  and 
is  used  to  some  extent  to  force  the  beer  through  the  various  pipes  from  the  storage 
cellar  to  the  place  where  it  is  drawn  into  casks  or  bottles,  thus  replacing  pumps  with 
their  contaminations.  It  is  also  used  in  the  cooling  machines,  being  circulated 
through  the  coils  instead  of  brine  or  water.  It  is  very  satisfactory  for  this  purpose, 
since  the  escaping  gas  does  no  harm  in  case  there  is  a  leak.  About  2200  pounds  of 
liquid  carbon  dioxide  are  said  to  be  obtained  from  600  barrels  of  wort.  A.  Marcet, 
J.  Soc.  Chem.  Ind.,  1894,  825. 


FERMENTATION  INDUSTRIES  403 

some  actively  fermenting  young  beer.  The  yeast  cells  attach  them- 
selves to  the  shavings,  and  the  beer  is  left  clear. 

Top  fermentation  is  usually  employed  in  England,  and  largely  in 
this  country  for  ales,  etc.  The  fermentation  is  very  active,  usually 
ending  in  from  three  to  five  days,  and  the  yeast  is  partly  carried  to 
the  surface  of  the  wort  by  the  rapid  evolution  of  the  carbon  dioxide. 
A  certain  amount  of  bottom  yeast  is  also  formed.  The  top  yeast  is 
removed  by  skimming,  and  the  beer  is  drawn  into  small  casks  hold- 
ing from  two  to  four  barrels  each  for  the  after  fermentation.  These 
casks  are  placed  in  a  cold  room,  and  the  process  goes  on  until  most 
of  the  yeast  has  been  forced  out  of  the  bung-hole.  The  cask  is  then 
bunged  and  allowed  to  stand  until  the  sediment  has  deposited,  when 
the  clear  beer  is  drawn  off  into  barrels  for  market.  Isinglass  or 
gelatine  is  often  added  to  assist  in  settling  the  sediment. 

Top  fermentation  is  favorable  to  the  development  of  other  fer- 
ments, and  a  high  percentage  of  alcohol  is  often  depended  upon  to 
prevent  these  growths.  In  order  to  increase  the  alcohol  and  dextrin 
without  increasing  the  quantity  of  malt,  it  is* frequently  customary 
to  add  sugar  or  glucose  to  the  wort  in  the  brewing  kettle. 

During  the  fermentation  the  contents  of  the  tub  are  stirred  occa- 
sionally to  aerate  the  wort.  The  progress  of  the  fermentation  is 
judged  by  the  readings  of  a  hydrometer,  and  as  the  density  of  the 
wort  decreases  as  the  fermentation  advances,  the  process  is  called 
"attenuation."  The  temperature  is  carefully  watched,  and  not 
allowed  to  rise  above  18°  C. 

Besides  alcohol  and  carbon  dioxide,  beer  contains  glycerine,  suc- 
cinic  acid,  amides,  peptones,  and  dextrins.  Phosphoric,  acetic,  and 
lactic  acids  are  also  present  in  a  small  quantity.  All  the  soluble 
constituents  of  the  beer,  except  the  alcohol  and  carbon  dioxide,  and 
which  give  it  its  nutritive  qualities,  are  grouped  together  under  the 
name  of  "  extract."  English  ales,  porters,  and  stouts  are  rich  in 
extract,  but  most  German  and  American  beers  contain  only  a  moder- 
ate amount  of  it. 

Sometimes  beer  is  flavored  with  bitter  substances,  such  as  quas- 
sia and  gentian  root ;  or  ginger  or  coriander  may  be  added  for  pun- 
gency, but  this  is  prohibited  in  many  countries. 

Bottling  or  Barrelling.  —  Much  of  the  success  with  which  certain 
beers  meet  in  commerce  is  due  to  the  care  exercised  on  this  point. 
The  barrels  are  coated  on  the  inside  with  brewers'  pitch,  a  mixture 
of  rosin  and  rosin  oil  which  softens  at  50°  to  60°  C.  This  prevents 
the  beer  from  soaking  into  the  staves  and  extracting  color  or  flavor 


404  OUTLINES  OF  INDUSTRIAL   CHEMISTRY 

from  the  wood.  All  barrels,  and  especially  old  ones  which  are  re- 
turned for  refilling,  should  be  thoroughly  scalded  and  washed  out. 
If  this  is  not  done  the  beer  is  liable  to  sour  before  it  reaches  the  con- 
sumer. It  is  frequently  customary  to  fume  the  barrels  with  sulphur 
dioxide  or  to  wash  them  with  sulphurous  acid  or  bisulphite  solution. 
The  practice  of  adding  a  certain  proportion  of  calcium  or  potassium 
bisulphite  to  each  barrel  of  beer  before  shipment  is  nearly  univer- 
sal. This  prevents  the  development  of  injurious  ferments.  Sali- 
cylic acid  is  often  added  to  improve  the  keeping  qualities,  but  with 
doubtful  benefit  to  the  consumer. 

Bottles  must  be  clean  and  only  the  best  quality  of  corks  should 
be  used.  Bottled  beer  is  usually  "  Pasteurized  "  at  60°  C.  for  about 
an  hour.  It  is  very  essential  that  both  barrels  and  bottles  should  be 
entirely  full,  for  if  an  air  space  is  left  the  beer  becomes  flat  and 
stale. 

The  quality  of  beer  depends  mainly  on  the  purity  of  the  water 
and  yeast  employed,  and  upon  the  care  taken  to  keep  all  parts 
of  the  brewery  exceedingly  clean.  All  vats,  tubs,  coolers,  and  pans 
must  be  thoroughly  washed  and  scalded  immediately  after  use,  and 
the  floors  and  walls  of  the  brewery  must  be  perfectly  clean. 

Various  kinds  of  beers  are  recognized  in  commerce,  according  to 
the  appearance,  mode  of  preparation,  flavor,  strength  of  alcohol  and 
of  extract,  etc. 

Ale  is  a  light-colored  beer,  often  rather  strong  in  alcohol,  and 
made  by  top  fermentation  with  the  use  of  a  large  amount  of 
hops. 

Porter  is  a  dark-colored  beer,  containing  much  sugary  matter  and 
extract.  For  this,  the  malt  is  kiln-dried  at  such  a  high  temperature 
that  it  is  partially  charred,  forming  caramel  which  colors  and  flavors 
the  beer. 

Stout  is  similar  to  porter,  but  contains  more  alcohol  and  extract. 

Lager  beer  is  made  by  bottom  fermentation,  is  rather  low  in 
alcohol,  and  contains  a  moderate  amount  of  extract.  Export  lagers 
are  made  from  stronger  worts  and  contain  more  alcohol  and  extract. 
A  special  brew  made  in  the  spring  from  very  concentrated  wort  and 
but  little  hops  is  called  bock  beer  or  Salvator  beer.  It  contains 
much  unfermented  sugar  and  will  not  keep  long. 

Berlin  weiss-bier  is  made  from  a  mixture  of  three  parts  malted 
wheat  to  one  of  barley  malt.  It  is  fermented  by  top  fermentation, 
and  is  usually  bottled  before  the  after  fermentation  is  ended.  Thus 
it  contains  much  carbon  dioxide  and  foams  excessively.  It  is  very 
light-colored  and  contains  lactic  acid. 


FERMENTATION   INDUSTRIES 


405 


The  following  table  shows  the  average  composition  of  beers  ac- 
cording to  various  authors  :  — 


SP.  GR. 
(17.5°  C.) 

ALCOHOL. 

EXTRACT. 

ACIDS. 
(Acetic,  Lactic,  etc.) 

ASH. 

Vienna  lager  *     .... 

1.017 

3.70 

5.71 

0.008 

— 

Pilsner  lager  *     .... 

1.016 

3.43 

5.45 

0.008 

— 

Munich  export  *  .... 

1.020 

3.94 

6.72 

0.010 

— 

Munich  Salvator  *    ... 

— 

4.78 

10.67 

— 

— 

Berlin  Weiss-bier*  .     .     . 

1.012 

2.82 

4.21 

— 

— 

Burton  pale  ale  I      ... 

— 

5.37 

5.13 

0.16 

0.55 

Dublin  stout  XXX  t     .    •  . 

— 

6.78 

9.52 

0.29 

1.40 

Milwaukee  lager  J    .     .     . 

1.010 

4.28 

4.18 

0.057 

0.196 

Milwaukee  Bavarian  J  .     . 

1.0187 

5.06 

6.26 

0.074 

0.346 

St.  Louis  export  J     . 

1.0178 

4.40 

6.15 

0.067 

0.312 

Philadelphia  lager  t       .     . 

1.0147 

4.29 

5.22 

0.086 

0.241 

*  Ost,  Technischen  Chemie,  p.  455. 

t  Allen,  Commercial  Organic  Analysis,  Vol.  II,  2d  Ed.,  p.  92. 

J  Crampton,  U.  S.  Dep't  Agriculture,  Bulletin  No.  13,  part  3,  p.  282. 

DISTILLED  LIQUORS 

Distilled  liquors  are  obtained  by  distilling  alcoholic  liquids  pre- 
pared by  fermentation.  They  are  essentially  mixtures  of  ethyl 
alcohol  and  water  in  varying  proportions  with  minute  quantities  of 
organic  ethers  and  higher  alcohols.  Pure  ethyl  alcohol  may  be  con- 
sidered the  representative  and  chief  constituent  of  these  liquors. 
When  first  distilled  they  contain  neither  extractive  nor  mineral 
matter,  and  are  much  stronger  in  alcohol  than  fermented  liquors. 

Alcohol  is  always  prepared  on  a  technical  scale  by  fermenting 
sugar,  which  in  most  cases  is  derived  from  starch  by  conversion  with 
diastase,  or  from  the  molasses  of  the  sugar  industry.  In  the  United 
States  the  materials  employed  are  corn,  rye,  and  barley ;  in  England, 
barley,  rice,  corn,  and  rye  are  used ;  while  in  Germany,  the  potato 
and  molasses  are  the  principal  sources.  The  products  obtained  from 
these  several  raw  materials  vary  somewhat  in  their  character,  flavor, 
and  strength. 

Since  the  largest  possible  yield  of  alcohol  is  desired  from  a  given 
amount  of  starchy  material,  the  latter  is  so  treated  that  the  most 
complete  conversion  into  maltose  is  obtained  with  as  little  dextrin 
as  may  be.  This  is  accomplished  by  treating  the  starchy  material 
with  malt  prepared  with  the  view  of  obtaining  all  the  diastase  pos- 
sible. For  this  purpose,  the  germination  is  stopped  earlier  and  the 


406  OUTLINES   OF   INDUSTRIAL  CHEMISTRY 

drying  temperature  kept  lower  than  in  the  case  of  malt  for  brew- 
ing. The  preparation  of  pure  alcohol  from  corn  is  carried  on  abont 
as  follows:  The  corn,  usually  degerminated,  is  ground  to  a  coarse 
meal  between  rolls,  and  a  weighed  amount  of  this  meal  is  run 
into  a  closed  iron  digester  (called  a  "  cooker  ")  provided  with  a  stir- 
ring apparatus.  Here  it  is  mixed  with  water  and  heated  by  steam 
under  pressure  of  two  or  three  atmospheres  for  an  hour  or  two.  It 
is  then  blown  out  into  another  vessel ;  or  it  may  be  cooled  in  the 
cooker.  (The  cooling  is  sometimes  hastened  by  exhausting  the  air 
from  the  vessel  by  a  pump.)  As  soon  as  the  temperature  reaches 
63°  C.,  the  required  amount  of  ground  malt,  mixed  with  a  little 
water,  is  added  and  the  mass  thoroughly  stirred.  The  temperature 
must  not  be  allowed  to  go  above  63°  C.,  in  order  that  the  least  pos- 
sible amount  of  dextrin  may  be  formed.  The  resulting  wort  is 
drawn  off  through  a  sieve  to  remove  the  husks  of  the  grain,  which 
are  washed  with  hot  water  and  the  washings  added  to  the  wort. 
The  latter  is  then  rapidly  cooled  (to  prevent  the  development  of 
acetic  fermentation)  and  drawn  into  the  fermenting  vats.  These 
are  very  large  cylindrical  wooden  tubs,  sometimes  25  feet  deep  and 
20  feet  in  diameter.  A  distillery  usually  has  6  of  these  tubs,  one 
being  emptied  and  recharged  every  day.  The  fermentation  of  the 
wort  is  started  by  adding  yeast,  as  in  the  case  of  brewing ;  but  for 
alcohol,  the  quantity  of  yeast  and  the  temperature  of  fermentation 
are  regulated  with  the  view  of  converting  all  the  sugar  into  alcohol 
as  rapidly  and  completely  as  possible.  The  legal  limit  of  the  time 
for  fermentation  is  72  hours,  hence  the  distiller  must  force  the 
process  to  convert  all  the  sugar  of  his  wort.  Moreover,  too  slow 
fermentation  is  favorable  to  the  development  of  the  acetic  and 
lactic  fermentations,  with  consequent  loss  of  alcohol.  The  tempera- 
ture is  therefore  high,  being  20°  to  25°  C.,  and  a  very  active  top  fer- 
mentation is  carried  on.  But  these  conditions  produce  an  increased 
amount  of  fusel  oil.  If  the  temperature  rises  much  above  25°  C., 
a  notable  loss  of  alcohol  through  evaporation  occurs.  During  the 
final  part  of  the  fermentation,  a  portion  of  the  dextrin  in  the  mash 
is  converted  into  maltose  by  the  diastase  still  remaining,  and  this 
sugar  is  then  fermented  by  the  yeast.  The  malt  liquor  boils  and 
sputters  in  the  tub,  but  any  undue  amount  of  frothing  is  combatted 
by  sprinkling  oil  on  the  surface. 

To  prevent  the  development  of  bacteria  and  wild  yeasts,  it  is  now 
often  customary  to  add  a  little  hydrofluoric  acid  or  alkali  fluoride 
to  the  mash,  after  the  conversion  of  the  starch  by  the  diastase.  It 
increases  the  yield  of  alcohol  by  preventing  these  secondary  fer- 


FERMENTATION  INDUSTRIES  407 

mentations,  and  tends  to  reduce  frothing.  It  is  also  recommended 
as  a  disinfectant  and  germicide  for  general  cleaning  purposes  in  the 
vats  and  tubs. 

When  the  fermentation  ceases,  the  mash  consists  of  a  mixture 
of  slimy,  solid  matter,  with  water,  alcohol,  fusel  oil,  acids,  etc.  The 
amount  of  alcohol  varies  from  10  to  13  per  cent  by  volume,  and  is 
separated  from  the  other  constituents  by  distillation.  This  was 
formerly  carried  on  in  simple  stills,*  heated  by  direct  firing,  and 
connected  with  a  condensing  worm.  They  were  intermittent  in 
action  and  yielded  a  very  dilute  distillate,  which  had  to  be  re- 
peatedly redistilled  to  obtain  a  strong  alcohcl;  thus,  e.g.,  from  a 
mash  containing  10  per  cent  alcohol,  the  first  distillate  contains 
about  28  per  cent  alcohol ;  by  redistilling  this  distillate,  the  alcohol 
percentage  is  raised  to  50  per  cent ;  by  another  redistillation  it  is 
raised  to  70  per  cent,  and  this  in  turn,  yields  an  80  per  cent  alcohol. 
By  many  redistillations,  an  alcohol  of  95  per  cent  may  be  obtained, 
but  above  this  redistillation  yields  no  further  separation. 

But  the  principle  of  fractional  condensation  is  now  employed, 
and  improved  stills,  with  dephlegmation  and  rectifying  apparatus, 
make  it  possible  to  obtain  concentrated  alcohol  by  two  distillations. 
And  further,  the  old  interrupted  working  has  now  given  way  to 
continuous  processes,  by  which  the  inflow  of  mash  and  the  outflow 
of  exhausted  mash  (slops)  are  unbroken. 

For  distilling  potato  mashes,  which  are  thick  and  slimy,  no 
continuous  acting  still  has  proved  successful,  and  the  intermittent 
Pistorius  apparatus,  consisting  of  two  connected  stills  and  a  de- 
phi  egmator  is  much  used.  For  distilling  wines  for  brandy,  the 
Savalle  apparatus  is  generally  employed.  The  Coffey  still  in 
various  modified  forms  is  largely  used  for  grain  mashes;  the 
mash|  enters  the  analyzer  hot  after  having  passed  through  the 
rectifier.  From  the  top  plates  of  the  rectifier,  the  alcohol  vapor 
passes  into  a  copper  condensing  worm,  which  empties  into  a  small 
box  with  glass  sides,  through  which  the  density  of  the  liquid  may 
be  observed  by  means  of  an  hydrometer  floating  in  it.  The  box  is 
locked  and  sealed  by  the  revenue  officer  stationed  in  the  distillery, 
and  the  distiller  has  no  access  to  the  liquor.  It  overflows  into  tanks 

*  The  old  pot  stills  are  now  used  for  the  distillation  of  certain  drinkable  spirits 
(especially  whiskey),  but  they  are  uneconomical  of  fuel  and  time. 

t  By  its  passage  through  the  still,  the  mash  is  entirely  deprived  of  its  alcohol, 
but  the  non-volatile  matter,  consisting  of  fats,  protein,  undecomposed  starch,  and 
other  non-nitrogenous  bodies,  flows  continuously  from  the  waste  pipe  of  the  si  ill. 
This  residue  usually  contains  over  90  per  cent  water,  and  is  often  fed  as  "  slop  "  to 
cattle. 


408  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

where  it  is  gauged  by  the  revenue  officer  as  crude  or  raw  spirits. 
It  contains  some  aldehyde  and  fusel  oil ;  the  latter,  constituting  the 
greater  part  of  the  impurities  present,  imparts  a  nauseous  odor  and 
taste,  and  is  removed  by  further  purification.  The  raw  spirit  is 
diluted  with  water  and  run  through  a  wood-charcoal  filter  similar  in 
form  to  the  bone-char  filter  used  for  glucose ;  the  charcoal  absorbs 
the  fusel  oil.  Another  method  (that  of  Bang  and  Ruffin)  is  to  treat 
the  alcohol  with  caustic  soda  and  then  with  dilute  sulphuric  acid  to 
destroy  the  aldehydes ;  the  diluted  alcohol  is  then  agitated  with 
petroleum  distillates  boiling  slightly  above  100°  C.  The  petroleum 
oil  probably  absorbs  the  fusel  oil. 

The  dilute  purified  alcohol  is  then  rectified  in  a  still  provided 
with  a  column  or  dephlegmator  tower,  similar  to  the  Coupier  still 
or  French  column  apparatus,  Figs.  5  and  6.  Savalle's  apparatus 
is  largely  used  abroad.  Rectification  is  an  intermittent  process,  the 
still  being  entirely  emptied  and  cleaned  before  a  new  charge  is 
introduced.  The  boilers  are  very  large  and  are  usually  made  of 
iron. 

The  products  of  the  distillation  are  divided  according  to  their 
character  and  percentage  of  alcohol,  into :  — 

(a)  First   runnings,  consisting  of  some  alcohol,  with  aldehyde 
and  ethers. 

(b)  Cologne  spirit,  a  very  pure  distillate,  with  about  96  per  cent 
of  alcohol. 

(c)  Common  alcohol,  containing  about  80  to  95  per  cent  alcohol. 

(d)  Alcohol  No.  2,  a  weak  distillate. 

(e)  Fusel  oil. 

These  distillates  are  separated  by  the  revenue  officer,  who  turns 
the  flow  from  one  receiver  into  the  next,  according  to  the  densities 
shown  by  the  hydrometer  floating  in  a  glass  box  similar  to  that  de- 
scribed on  p.  407,  and  through  which  the  distillates  pass.  First 
runnings  are  usually  sold  to  chemical  works,  as  are  also  fusel  oils. 
Cologne  spirit  and  No.  1  alcohol,  which  generally  constitute  by  far 
the  largest  part  of  the  distillate,  are  sold  as  such  to  the  dealer. 
Alcohol  No.  2  may  be  redistilled,  but  is  usually  diluted  with  water 
to  bring  the  alcohol  to  about  50  per  cent,  and  is  then  stored  in  oak 
barrels  to  "  age,"  after  which  it  is  usually  sold  as  "  whiskey."  During 
the  aging  the  fusel  oil  in  the  liquor  is  broken  up  or  formed  into 
ethers,  thus  removing  the  nauseous  odor  and  taste  of  the  raw  spirit. 
The  longer  the  aging,  the  more  complete  the  removal  of  the  fusel  oil 
and  the  richer  the  flavor  of  the  liquor  becomes.  It  also  extracts 
some  coloring  matter  from  the  wood  of  the  barrel,  and  thus  in  time 


FERMENTATION  INDUSTRIES  409 

acquires  the  light  reddish-brown  shade  of  the  commercial  whiskey. 
But  this  color  is  now  very  generally  imitated  by  adding  some 
caramel. 

The  Coffey  still  and  others  on  the  same  principle  are  well 
adapted  to  the  production  of  pure  alcohol,  or,  as  it  is  generally 
called  in  England,  "  silent  spirit,"  since  it  has  no  special  odor  nor 
flavor  to  distinguish  its  origin,  as  is  the  case  when  pot  stills  are 
used. 

In  all  countries,  the  manufacture  of  strongly  alcoholic  liquors  is 
made  a  means  of  raising  revenue  by  the  government.  Consequently 
these  industries  are  subject  to  constant,  and  often  annoying,  inter- 
ferences by  the  revenue  officials,  and  many  burdensome  laws  are 
enacted,  presumably  to  prevent  fraud.  In  this  country,  both  the 
malt  and  the  grain  used  in  the  mash  are  weighed  by  the  revenue 
officer,  the  time  of  fermentation  is  limited  to  three  days,  and  the 
entire  process  of  distillation  is  conducted  under  the  direct  super- 
vision of  the  inspector.  The  amount  of  crude  spirit  produced  is 
gauged  by  the  officer,  and  also  the  quantities  of  the  several  grades 
of  rectified  alcohol  produced,  and  these  are  run  directly  from  the 
still  into  storage  tanks  in  the  government  storehouse.  From  these 
tanks  it  is  soon  drawn  into  barrels  (which  must  be  new),  and  each 
cask  is  at  once  gauged  by  the  officers,  and  the  number  of  gallons 
of  absolute  alcohol  contained  in  the  liquor,  and  upon  which  the  tax 
must  be  paid,  is  determined.  The  cask  is  then  put  into  the  bonded 
warehouse,  where  it  may  remain  eight  years  by  the  present  law,  but 
at  the  end  of  four  years  the  tax  must  be  paid.  The  present  tax  is 
$1.10  per  proof  gallon  of  50  per  cent  alcohol  (by  volume),  or  $2.07 
per  standard  gallon  (231  cubic  inches),  of  94  per  cent  alcohol.  The 
cost  of  making  a  gallon  of  cologne  spirit  is  less  than  20  cents.  This 
tax  is  a  heavy  burden  on  many  industries  which  use  alcohol  for 
manufacturing  purposes,  especially  in  varnish-making  and  the  coal- 
tar  dye  industries.  The  law  permitting  untaxed  alcohol  to  be  used 
in  the  arts  has  not  yet  been  put  into  operation. 

In  England  the  revenue  tax  is  much  higher  than  in  this  country, 
being  10s.  6d.  per  gallon  of  proof  spirit.*  But  the  law  permits  the 
preparation  of  "methylated  spirit,"  consisting  of  90  per  cent  alco- 
hol, to  which  10  per  cent  of  crude  methyl  alcohol  (wood  spirits, 
p.  259)  has  been  added.  This  is  free  of  tax,  since  the  liquor  is  pre- 
sumed to  be  undrinkable,  bat  serves  very  well  for  many  technical 

*  Proof  spirit  is  alcohol  of  such  strength  that  13  gallons  of  the  spirit  have  the 
same  weight  as  12  gallons  of  distilled  water  at  10°  C.  Proof  spirit  contains  49.24  per 
cent  of  absolute  alcohol,  by  weight. 


410  OUTLINES  OF   INDUSTRIAL  CHEMISTRY 

purposes,  and  for  burning  in  alcohol  lamps.  In  Germany  a  similar 
provision  exists,  but  in  addition  to  wood  spirits,  a  certain  amount  of 
pyridine  (bone  oil)  must  also  be  added.  This  gives  the  "denat- 
urated"  alcohol  a  very  offensive  odor,  bat  does  not  injure  it  for 
many  uses. 

The  fusel  oil  consists  mainly  of  amyl  alcohol,  with  some  butyl, 
propyl  and  allyl  alcohols.  It  is  always  present  in  crude  spirits,  and, 
to  a  small  extent,  in  the  rectified  alcohol  and  liquors.  It  is  gen- 
erally supposed  to  have  a  very  destructive  action  on  the  health,  and 
its  complete  removal  from  liquors  has  always  been  insisted  upon. 
But  recent  experiments*  tend  to  show  that,  aside  from  the  nauseous 
odor  and  flavor  which  it  imparts  to  the  liquor,  it  has  very  little,  if 
any,  injurious  effect  on  the  system.  The  results  ascribed  to  it  are 
probably  due  to  common  alcohol.  Fusel  oil  (amyl  alcohol)  is  used 
largely  in  the  preparation  of  the  so-called  "  fruit  essences,"  which 
are  organic  ethers,  and  which  are  used  in  ice  cream,  soda  water, 
sherbets,  etc. 

Alcohol  is  extensively  used  in  the  arts  as  a  solvent ;  in  per- 
fumery; for  making  various  essences,  tinctures,  and  extracts  in 
pharmacy ;  for  vinegar-making ;  and  in  chemical  manufacturing  for 
preparing  ether,  chloral,  chloroform,  ethyl  nitrite,  and  various  ethyl 
derivatives,  especially  for  use  in  the  coal-tar  dye  industry.  A  con- 
siderable amount  is  used  in  museums  for  preserving  anatomical  and 
other  specimens. 

Whiskey  is  a  distilled  liquor  made  from  fermented  grain  mash. 
The  malt  having  been  dried  over  an  open  fire,  retains  an  empy- 
reumatic  flavor,  which  reappears  in  the  product.  The  mash  is 
prepared  as  already  described  for  alcohol ;  after  fermentation  it  is 
distilled  from  a  pot  still  or  copper,  and  the  distillate  condensed 
in  a  worm,  without  any  attempt  at  dephlegmation.  A  little  soap  is 
often  put  into  the  still  to  prevent  frothing.  The  first  product, 
called  "  low-wines,"  is  redistilled,  and  yields  foreshots,  clean  spirit 
(whiskey),  and  feints,  while  spent  lees  are  left  in  the  still.  The 
foreshots  and  feints  are  redistilled  with  the  next  charge,  while  the 
clean  spirit  is  dilated  with  water  to  about  50  to  60  per  cent  of  alco- 
hol, and  then  put  in  bond  to  age  until  the  fusel  oil  flavor  disappears. 
As  a  rule  whiskeys  are  now  mixed  with  some  silent  spirit  made  with 
a  Coffey  still.  When  first  distilled,  whiskey  is  colorless ;  but  it  takes 
coloring  matter  from  the  wood  of  the  casks  while  aging. 

Much  artificial  whiskey  is  made  in  this  country  by  "  compound- 

*  J.  Soc.  Chem.  Ind.,  1891,  312.    A.  H.  Allen. 


FERMENTATION   INDUSTRIES  411 

ing."  Strong  alcohol  is  diluted  with  water  to  a  strength  of  50  to  55 
per  cent  by  volume,  colored  with  caramel,  and  a  very  small  quantity 
of  essential  oils  or  flavoring  substances  is  added  to  imitate  the  odor 
and  taste  of  the  natural  whiskey.  The  empyreumatic  flavor  is 
obtained  by  adding  a  few  drops  of  creosote  to  each  barrel. 

Gin  contains  about  40  per  cent  of  alcohol,  and  is  made  from  a 
fermented  grain  mash  in  much  the  same  way  as  alcohol,  but  the 
distilled  liquor  is  left  colorless,  and  is  flavored  by  distilling  in  pot 
stills  with  juniper  berries,  anise  seed,  coriander,  cardamon  seeds, 
calamus  root,  or  fennel.  The  best  gin  is  made  in  Holland,  at  Schie- 
dam, from  rye  mash,  and  is  distilled  only  in  pot  stills,  with  juniper 
berries. 

Brandy  is  made  by  distilling  wine,  or  the  fermented  juice  of  other 
fruit,  such  as  apples,  peaches,  cherries,  blackberries,  etc.  The  best 
brandy  (Cognac)  is  made  by  distilling  a  good  quality  of  white  wine, 
but  much  inferior  stuff  is  made  by  distilling  low  grades  of  red  wine. 
It  is  customary  to  leech  the  solid  residues  from  wine-pressing  with 
water,  and  to  ferment  the  liquid  so  obtained ;  this  is  then  distilled 
for  inferior  brandy.  Cheap  brandies  are  distilled  directly  from  the 
wine,  but  fine  grades  are  rectified  once  or  twice.  The  distillate  is 
colorless,  but  takes  color  from  the  casks.  It  is  also  customary  to 
add  caramel.  Brandy  contains  from  47  to  54  per  cent  of  alcohol,  by 
volume,  and  owes  its  peculiar  flavor  to  oenanthic  ether.  Pot  stills 
are  always  used  in  order  to  preserve  the  flavors.  Cherry  brandy  is 
extensively  made  in  southern  Germany,  where  it  is  called  Kirsch- 
wasser.  Some  of  the  pits  are  crushed  and  added  to  the  fermented 
juice,  thus  flavoring  the  product  with  bitter  almond  and  prussic  acid. 
Imitation  brandy  is  made  from  grain  alcohol  by  diluting  and  adding 
various  flavoring  matters  (oenanthic  ether,  bitter  almonds,  catechu, 
etc.),  and  coloring  with  caramel. 

Rum  is  made  from  fermented  molasses  or  megass  (macerated 
crushed  sugar  cane).  It  is  twice  distilled,  and  the  new  rum  is  color- 
less and  has  a  disagreeable  odor,  which  is  removed  by  treating  with 
charcoal  and  storing  for  a  long  time.  It  is  often  colored  with  burnt 
sugar.  It  contains  about  55  per  cent  of  alcohol,  and  its  flavor  is 
due  to  ethyl  acetate  and  butrate.  Jamaica  rum  is  said  to  be  flavored 
by  putting  sugar  cane  leaves  in  the  still.  Ethyl  butrate  is  made  on 
a  large  scale,  and  sold  as  "  rum  essence,"  to  be  used  in  making  imi- 
tation rum  from  grain  spirit. 

Liqueurs  and  cordials  are  usually  strong  alcoholic  beverages  com- 
pounded from  grain  alcohol,  with  various  flavoring  essences.  They 
are  usually  flavored  with  cane  sugar. 


412  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

Arrack  is  made  by  distilling  the  fermented  juice  of  the  cocoanut 
palrn.  It  is  sometimes  flavored  with  poppy  or  hemp  leaves,  or  stra- 
monium juice.  A  distilled  liquor  made  from  malted  rice  is  often 
sold  as  arrack. 

Absinthe  is  made  in  much  the  same  way  as  gin,  but  is  flavored 
with  wormwood. 

VINEGAR 

Next  to  the  alcoholic  fermentation  in  technical  importance  is  the 
acetic  fermentation,  which  is  caused  by  a  group  of  bacteria.  These 
micro-organisms  cause  the  oxidation  of  the  alcohol,  probably  into 
aldehyde,  and  ultimately  into  acetic  acid,  thus :  — 

2  C2H5OH  +  02  =  2  C2H40  +  2  H20. 
2C2H40  +  02  =  2C2H402- 

The  specific  acetic  ferment  is  Bacterium  aceti,  but  the  related 
species,  B.  Pasteur  ianum,  B.  xylinum,  and  B.  Kutzingianum,,  doubtless 
cause  more  or  less  oxidation  of  the  alcohol.  For  this  oxidation  the 
liquid  must  not  contain  more  than  10  per  cent  of  alcohol,  and  certain 
nitrogenous  matters  suitable  for  the  nourishment  of  the  ferment 
must  be  present. 

The  materials  used  for  fermented  vinegar  are  cider,  wines,  decoc- 
tions made  from  malt,  beer  which  has  not  been  boiled  with  hops, 
beet  sugar  solutions,  diluted  alcohol  mixed  with  malt  infusion,  and 
occasionally  glucose  or  molasses.  The  acetic  ferment  propagates 
very  rapidly  in  a  liquid  containing  from  2  to  3  per  cent  of  alcohol, 
nitrogenous  matter,  and  phosphate  of  potassium,  calcium,  or  ammo- 
nium, if  the  temperature  is  kept  between  20°  and  35°  C.  A  thick 
film,  or  skin,  forms  on  the  surface  of  the  liquid,  and  finally  sinks, 
owing  to  its  increasing  weight,  forming  the  "vinegar  mother";  then 
the  formation  of  acid  ceases.  If  the  fermentation  is  very  active 
after  the  alcohol  is  all  converted,  the  resulting  acetic  acid  may  itself 
be  attacked  and  decomposed  into  water  and  carbon  dioxide.  This, 
however,  does  not  take  place  if  a  fresh  supply  of  alcoholic  liquor  is 
added.  Under  the  most  favorable  conditions  the  ferment  cannot  live 
in  a  liquid  containing  much  more  than  13  per  cent  of  acetic  acid. 

In  the  Orleans  process  of  making  vinegar  from  wine,  oak  casks  of 
about  300  litres  capacity  are  used.  The  cask  is  filled  about  one-third 
full  of  strong  vinegar  containing  some  ferment,  and  about  10  litres 
of  wine  (previously  filtered  through  beechwood  shavings  until  clear) 
are  added,  and  the  whole  allowed  to  stand  at  a  temperature  of  from 
25°  to  30°  C.  After  about  eight  days  the  wine  has  soured,  and  another 
portion  of  10  litres  of  wine  is  added.  This  process  is  repeated  until 


FERMENTATION   INDUSTRIES 

the  cask  is  about  half  full,  when  about  one-third  of  the  vinegar  is 
drawn  off,  and  the  process  of  adding  fresh  wine  is  resumed.  This 
goes  on,  under  favorable  circumstances,  for  several  years,  until  the 
cask  becomes  too  full  of  sediment ;  then  it  is  emptied,  and  .thoroughly 
cleaned  by  washing  and  scalding  with  hot  vinegar.  The  casks  have 
openings  at  the  top  for  the  admission  of  air,  and  the  fermentation  is 
largely  spontaneous. 

The  action  of  the  ferment  may  be  checked  if  the  temperature 
falls  too  low ;  or  if  the  wine  added  is  very  low  in  alcohol,  it  may 
not  support  the  ferment,  and  the  vinegar  is  decomposed  into  water 
and  carbon  dioxide.  The  ferment  may  also  be  weakened  or  destroyed 
by  the  presence  of  vinegar  eels,  Angaittida  aceti,  a  species  of  micro- 
scopic worm,  which  deprives  the  ferment  of  the  oxygen  needed  for 
its  propagation. 

The  Orleans  process  is  slow,  but  the  resulting  vinegar  has  a  fine 
flavor  and  aroma. 

Pasteur  suggested  a  modification  of  the  above  process,  in  which 
the  ferment  is  cultivated  in  a  suitable  liquid,  and  the  alcoholic  liquid 
is  added  regularly  when  the  "mother"  is  well  started.  When  the 
acid  formation  becomes  slow,  the  "mother"  is  collected  and  washed, 
and  used  to  start  a  new  fermentation. 

The  "  quick  vinegar  process  "  is  now  generally  practised  for  fer- 
menting malt  decoctions,  diluted  alcohol,  or  the  extract  from  any 
fermented  mash.  The  liquid  should  be  clear,  and  free  from  any 
sediment  or  slime.  The  fermentation  is  carried  on  in  tall  vats,  or 
casks,  about  12  feet  high  by  5  feet  in  diameter.  These  have  perfo- 
rated false  bottoms,  on  which  rests  the  filling  of  beech  wood  shavings, 
reaching  nearly  to  the  top  of  each  cask.  Over  the  shavings,  a  few 
inches  below  the  cover  of  the  cask,  is  a  perforated  wooden  plate, 
through  the  holes  of  which  short  pieces  of  twine  are  drawn;  4  or  5 
glass  tubes  are  set  in  this  plate,  to  permit  the  upward  passage  of  the 
air.  The  beech  shavings  are  boiled  in  water,  and  then  soaked  in 
strong  vinegar,  before  filling  into  the  vat.  Their  purpose  is  to 
spread  the  liquid  into  very  thin  films,  so  that  the  oxidation  may  be 
rapid.  They  also  serve  as  points  of  attachment  for  the  ferment; 
The  liquid  to  be  fermented,  a  mixture  of  dilute  alcohol  and  vinegar, 
is  fed  in  a  slow  stream  on  to  the  top  of  the  cover,  through  which  it 
percolates,  dripping  from  the  ends  of  the  twine,  upon  the  shavings. 
It  comes  in  contact  with  the  ferment  on  the  shavings,  and  with  the 
current  of  air  passing  up  through  the  mass,  and  the  alcohol  is  rapidly 
oxidized  into  acetic  acid.  The  temperature  within  the  vat  rises, 
causing  the  air  to  rise  and  escape  through  the  openings  in  the  top, 


414  OUTLINES   OF  INDUSTRIAL   CHEMISTRY 

while  fresh  air  enters  through  holes  in  the  sides  of  the  vat,  just  on  a 
level  with  the  false  bottom,  thus  causing  a  continual  circulation  of 
fresh  air  within  the  vessel.  The  temperature  is  shown  by  a  ther- 
mometer, and  is  kept  as  near  30°  C.  as.  possible,  by  regulating  the 
temperature  of  the  air  admitted  into  the  cask.  If  allowed  to  go  too 
high,  much  alcohol  is  lost  by  evaporation,  and  the  vinegar  is  weak. 
Too  rapid  an  air  current  also  evaporates  much  alcohol. 

The  vinegar  formed  collects  under  the  false  bottom,  and  flows  out 
through  a  siphon. 

If  the  liquor  does  not  contain  more  than  4  per  cent  of  alcohol,  it 
may  all  be  converted  by  one  passage  through  the  vat,  but  the  result- 
ing vinegar  is  weak.  Hence  it  is  customary  to  add  more  alcohol, 
and  run  the  liquor  through  the  cask  again.  Or,  as  is  often  done,  it 
flows  through  a  series  of  vats. 

A  very  exact  regulation  of  the  strength  and  flow  of  alcoholic 
liquid,  and  of  the  amount  of  air  admitted,  is  essential  to  successful 
working.  Pure  air  and  good  ventilation  of  the  room  are  also  neces- 
sary. Considerable  alcohol  is  lost  by  evaporation,  amounting,  even 
in  good  work,  to  about  15  to  20  per  cent  of  that  in  the  original 
liquid.  The  air  leaving  the  converters  is  often  washed  with  water 
to  recover  the  vaporized  alcohol  and  acetic  acid.  On  an  average, 
the  vinegar  produced  contains  about  6  per  cent  acetic  acid,  which 
may  be  increased  to  10  or  12  per  cent  by  proper  regulation  of  the 
process ;  there  is,  however,  a  consequent  diminished  yield  of  vinegar. 
The  time  required  to  produce  finished  vinegar  is  from  8  to  12  days. 
The  amount  of  alcohol  added  must  be  so  regulated  that  the  liquid 
leaves  the  vat,  still  containing  a  very  small  percentage  of  unchanged 
alcohol,  for,  if  it  is  all  converted,  the  oxidation  extends  to  the  acetic 
acid,  and  some  may  be  lost  through  decomposition  into  water  and 
carbon  dioxide. 

Many  accidents  cause  the  process  to  go  wrong,  and  much  care  is 
necessary  to  secure  regularity  of  product  and  yield.  If  vinegar  eels 
appear,  it  is  customary  to  kill  them  by  adding  hot  vinegar  until  the 
temperature  of  the  vinegar  running  out  of  the  cask  has  risen  to  50°  C. 

The  vinegars  made  from  different  sources  vary  in  color,  taste, 
specific  gravity,  and  other  properties. 

Cider  vinegar  is  usually  made  by  spontaneous  fermentation  of 
cider  in  barrels  with  open  bungs.  Sometimes  "mother"  is  added 
to  hasten  the  action.  It  is  yellow  or  brown  in  color,  has  an  odor 
resembling  apples,  and  contains  malic  acid. 

Wine  vinegar  is  light  yellow  or  red,  according  as  it  is  made  from 
white  or  red  wine,  that  made  from  the  former  being  considered  the 


FERMENTATION   INDUSTRIES  415 

better.  It  contains  tartaric  acid,  and  some  acid  potassium  tartrate, 
with  other  matters  derived  from  the  wine,  some  of  which  influence 
the  flavor  of  the  product.  It  has  a  particularly  agreeable  aroma  and 
taste,  and  is  considered  the  finest  for  table  use. 

Malt  and  beer  vinegars  are  brown  in  color,  and  contain  dextrin 
and  protein,  and  other  extractive  matters,  together  with  acetic  ether, 
which  impart  peculiar  odors  and  flavor  to  them.  They  also  contain 
phosphates  and  other  mineral  matter. 

Spirit  vinegars,  made  from  diluted  alcohol,  are  nearly  colorless, 
and  since  they  contain  little  or  none  of  the  extractive  matter  present 
in  fruit  or  malt  vinegars,  they  lack  much  of  the  flavor  and  odor  of 
these.  Sometimes  they  are  colored  with  caramel,  and  are  often 
flavored  with  one  or  more  of  the  characteristic  ingredients  of  cider, 
wine,  or  malt  vinegars,  and  sold  under  these  names. 

Very  weak  vinegar  will  not  bear  much  agitation  nor  handling 
without  decomposition;  it  is  often  the  practice  to  add  a  certain 
amount  of  sulphuric  acid,  under  the  pretence  of  preserving  the 
vinegar  when  shipped.  Good  vinegar,  however,  is  never  treated 
in  this  way  by  reputable  makers. 

Imitation  vinegar  is  often  made  from  dilute  acetic  acid  derived 
from  wood  distillation.  This  is  colored  with  caramel,  and  gen- 
erally flavored  with  acetic  ether ;  '  but  usually  contains  no  phos- 
phates, tartrates,  nor  other  substances  characteristic  of  true  vinegar. 
Traces  of  empyreumatic  matter  are  often  present,  which  may  give 
it  a  disagreeable  flavor. 

Vinegar  is  chiefly  consumed  as  a  condiment,  or  used  for  making 
pickles. 

LACTIC   ACID 

A  fermentation  of  some  technical  importance  is  that  produced  by 
certain  bacteria,  especially  Bacterium  acidi  lactici,  by  which  sugars 
are  converted  into  lactic  acid :  — 

C6H12O6  =  2  C2H4(OH)COOH. 

These  ferments  are  generally  distributed  on  the  surface  of  grains, 
fruits,  and  malt,  thus  finding  access  to  mashes  and  worts ;  under  favor- 
able circumstances  they  grow  exceedingly  rapidly,  and  cause  souring 
of  the  liquid.  But  since  they  cease  to  propagate  after  the  liquid 
contains  about  1  per  cent  of  lactic  acid,  and  as  this  acid  is  a  good 
protection  against  the  development  of  other  bacteria,  while  it  has 
but  little  effect  upon  yeast,  it  is  often  customary  to  allow  the  lactic 
fermentation  to  take  place  in  connection  with  the  alcoholic,  especially 
in  grain  mashes  for  alcohol. 


416  OUTLINES   OF  INDUSTRIAL   CHEMISTRY 

Lactic  acid,  CH3  •  CH(OH)  -  COOH,  is  prepared  by  fermenting  a 
sugar  solution,  and  neutralizing  the  acid  as  soon  as  formed,  with 
calcium  carbonate.  The  solution  of  calcium  lactate  is  concentrated, 
and  the  salt  decomposed  with  sulphuric  acid. 

Lactic  acid  forms  a  syrupy  liquid  which  is  now  used  in  dyeing  and 
calico  printing  as  a  substitute  for  tartaric  and  citric  acids.  An- 
timony lactate  is  used  in  place  of  tartar  emetic  in  mordanting. 

REFERENCES 

The  Chemistry  of  Wine.    G.  J.  Mulder.    Translated  by  H.  Bence  Jones.     Lon- 
don, 1857.     (Churchill.) 

Lehrbuch  der  Gahrungs  Cheraie.     Adolf  Mayer,  Heidelberg,  1874.    (Winter.) 
On  Fermentation.     P.  Schutzenberger,  New  York,  1876.     (Appleton  &  Co.) 
Traite"  general  des  Vins  et  de  leurs  Falsifications.     Emile  Viard,  Paris,  1884. 

(Savy.) 

Die  Bereitung,  Pflege  und  Untersuchung  des  Weins.    J.  Nessler,  Stuttgart,  1889. 
The  Micro-organisms  of  Fermentation.     A.  Jorgenson.     Translated  by  H.  T. 

Brown.    London,  1889. 
Traite"  pratique  de  1'Art  de  Faire  le  Vin.     Frederic  Cazalis,  Paris,  1890.     (G. 

Masson. ) 

L1  Art  de  Faire  le  Vin  avec  les  Raisins  sees.    J.  F.  Audibert,  Paris,  1891. 
Etudes  sur  la  Biere.     M.  L.  Pasteur,  Paris,  1876.     (Gauthier-Villars. ) 
Lehrbuch  der  Bierbrauerei.     Carl  Lintner,  Braunschweig,  1878.     (Vieweg.) 
Gahrungs-Chemie  fur  Praktiker.     Josef  Bersch,  Berlin.     (Wiegandt,  Hempel, 

und  Parey.) 

Vol.  I.     Die  Hefe  und  die  Gahrungs  Erscheinungen.     1879. 

Vol.  II.     Fabrikation  von  Malz,  Malzextract  und  Dextrin.     1880. 

Vol.  III.     Die  Bierbrauerei.     1881. 
The  Brewer,  Distiller,  and  Wine  Manufacturer.     John  Gardner,  Philadelphia, 

1883.     (Blakiston,  Son  &  Co.) 
The  Theory  and  Practice  of  Modern  Brewing.      Frank  Faulkner.     3rd  Ed. 

London,  1888.     (F.  W.  Lyon.) 
Handbuch  der  Bierbrauerei.     Conrad  Schneider  u.  Gottlieb  Behrend,  Halle  a. 

S.,  1891.     (W.  Knapp.^ 

Chemistry  in  the  Brewing  Room.     Chas.  H.  Piesse,  London,  1891. 
Manual  of  Brewing.     E.  G.  Hooper.     4th  Ed.     London,  1891.     (Sheppard  & 

St.  John.) 

A  Textbook  of  the  Science  of  Brewing.     E.  R.  Moritz  and  G.  H.  Morris,  Lon- 
don, 1891.     (E.  &  F.  N.  Spon.) 
La  Biere.     L.  Lindet,  Paris,  1892  (?). 

Les  Distilleries.     M.  Desire"  Savalle,  Paris,  1881.     (G.  Masson.) 
A  Practical  Treatise  on  the  Raw  Materials  and  the  Distillation  and  Rectification 

of  Alcohol.     Wm.  T.  Brannt,  Philadelphia,  1885,     (H.  C.  Baird  &  Co.) 
L'Alcool.    Albert  Larbaletrier,  Paris,  1888.     (Bailliere  et  Fils.) 
A  Treatise  on  Alcohol,  with  Tables  of  Spirit-Gravities.     Thomas  Stevenson, 

London,  1888.     (Gurney  &  Jackson.) 
Traite"  de  la  Distillation.    J.  Fritsch  et  E.  Guillemin,  Paris,  1890.     (G.  Masson.) 


EXPLOSIVES  417 

La  Fabrication  des  Liqueurs  et  des  Conserves.    M.  Ch.  Girard,  Paris,  1890. 

(J.  B.  Bailliere.) 
Nouveau  Manuel  complet  de  la  Distillation  des  Grains  et  des  M  Classes.     Albert 

Larbaletrier  et  M.  F.  Malepeyre,  Paris,  1890. 
Les  Appareils  de  Distillation  et  de  Rectification.     Emile  Barbet,  Paris,  1890. 

(G.  Masson.) 
Traite"  de  la  Fabrication  des  Liqueurs  et  de  la  Distillation  des  Alcools.     P. 

Duplais,  2  vols.,  Paris,  1891.     (Gauthier-Villars.) 
Das  Flussaureverfahren  in  der  Spiritusfabrikation.     M.  Maercker,  Berlin,  1891. 

(P.  Pavey.) 

La  Rectification  de  PAlcool.     E.  Sorel,  Paris,  1894  (?).     (G.  Masson.) 
Cheinie  du  Distillateur.     M.  P.  Guichard,  Paris,  1895.     (Bailliere.) 
Industrie  de  la  Distillation,  Levures  et  Alcools.     M.  P.  Guichard,  Paris,  1897. 

(Bailliere.) 

Etudes  sur  le  Vinaigre.     M.  Pasteur,  Paris,  1868. 

Acetic  Acid  and  Vinegar,  etc.    John  Gardner,  London,  1885.     (Churchill.) 
Vinegar :  —  A  Treatise  on  the  Manufacture  of  Vinegar.     Win.  T.  Brannt,  Phila- 
delphia, 1890.     (Baird  &  Co.) 
Die  Essigfabrikation.    J.  Bersch.    4te  Auf.    Wien,  1895. 


EXPLOSIVES 

Explosives  are  chemical  compounds  or  mechanical  mixtures  which 
are  capable  of  very  rapid  decomposition  or  combustion,  upon  the 
application  of  a  shock,  or  of  a  small  amount  of  heat.  Through 
the  agency  of  chemical  action  they  suddenly  generate  large  volumes 
of  gas,  which  is  heated  to  a  high  temperature  at  the  moment  of 
liberation.  Explosives  comprise  gases,  liquids,  and  solids.  Explo- 
sive gas  mixtures  will  not  be  considered  here,  since  they  have  no 
technical  application,  though  often  introducing  very  dangerous  com- 
plications in  certain  technical  processes.  Liquid  explosives,  except- 
ing only  nitroglycerine,  which  is  seldom  used  in  the  liquid  condition, 
have  little  or  no  industrial  importance,  since,  being  extremely  sensi- 
tive to  shocks  and  heat,  they  are  too  dangerous  to  handle  or  transport; 
for  the  same  reasons  many  endothermic  bodies,  such  as  the  halogen 
compounds  of  nitrogen,  and  the  diazo-bodies  are  not  employed. 

When  the  combustion  takes  place  under  such  conditions  that  the 
gases  formed  cannot  readily  escape,  a  very  high  pressure  is  suddenly 
developed,  liberating  such  a  great  amount  of  heat  that  the  entire 
mass  is  instantly  decomposed  with  explosive  violence.  In  the  same 
way  if  an  explosive  is  subjected  to  a  sudden  and  extremely  high 
pressure  the  entire  mass  instantly  explodes.  This  latter  form  of 
decomposition  is  called  "detonation,"  and  is  usually  caused  by  ex- 

2E 


418  OUTLINES  OF   INDUSTRIAL   CHEMISTRY 

ploding  a  small  quantity  of  some  violent  explosive,  such  as  fulminate 
of  mercury,  or  silver,  in  contact  with  the  substance  to  be  detonated. 

The  energy  of  an  explosive  is  mainly  determined  by  the  amount 
of  gaseous  products  formed  by  its  decomposition,  the  rapidity  of 
their  evolution,  and  the  temperature  to  \vhich  these  gases  are  heated. 
It  has  been  calculated  that  the  explosion  of  one  cubic  kilogram  of 
dynamite,  measuring  9  cm.  on  the  side  of  the  cube,  occupies  ^^QU"  °^ 
a  second,  while  the  same  weight  of  ordinary  black  powder  requires 
y-J-^  of  a  second.  But  the  volume  of  gas  set  free  by  the  dynamite  is 
about  530  litres  when  reduced  to  0°  C.  and  at  760  mm.  pressure ; 
while  the  gas  from  gunpowder,  under  the  same  conditions  of  tem- 
perature and  pressure,  amounts  to  about  270  litres.  Moreover,  the 
temperature  of  the  gas  from  the  dynamite  is  very  much  higher  than 
is  that  from  gunpowder. 

Nearly  all  explosions  caused  by  chemical  action  are  merely  rapid 
oxidations  of  substances  containing  carbon,  hydrogen,  or  nitrogen. 
The  slower  the  oxidation  the  weaker  the  explosion,  while  for  the 
most  energetic  action  the  combustion  must  be  practically  instanta- 
neous. The  speed  of  the  oxidation  depends  largely  on  the  size  of 
the  particles  of  the  explosives,  and  also  upon  their  composition. 
Chemically  homogeneous  substances  are  usually  more  powerful  ex- 
plosives than  the  most  carefully  prepared  mixtures,  since  in  the 
former  the  combustion  is  propagated  from  molecule  to  molecule  more 
rapidly. 

Explosives  which  decompose  suddenly  cause  a  very  different 
result  than  those  which  are  slow  burning.  The  former,  even  when 
exploded  in  the  open  air,  have  a  shattering  action  upon  any  sub- 
stance with  which  they  are  in  contact.  They  are  used  in  hard  rock 
blasting,  especially  where  large  pieces  of  the  stone  are  not  desired, 
or  when  the  rock  is  full  of  cracks  or  seams ;  fewer  drill  holes  are 
needed,  and  the  rock  is  shattered  for  some  distance  away  from  the 
blast.  But  for  military  purposes,  for  quarrying  and  blasting  in  soft 
rock  or  coal,  slow  burning  powder  is  preferable  to  the  more  powerful 
dynamite. 

Gunpowder  is  a  mechanical  mixture,  and  is  the  oldest  and  a  very 
important  explosive.  Tradition  assigns  its  discovery  to  Berthold 
Schwartz,  a  monk  at  Frieburg,  Germany,  in  the  fourteenth  century, 
and  it  was  used  at  the  battle  of  Crecy  in  1346,  and  again  at  Augsburg 
in  1353.  It  was  probably  derived  from  the  formula  of  the  "  Greek 
fire  "  of  the  Orient.  Its  constituents  are  potassium  nitrate,  sulphur, 
and  charcoal.  Since  these  must  be  very  pure,  the  manufacturer 
generally  purifies  them.  Only  roll  brimstone  is  used,  and  this  is 


EXPLOSIVES  419 

sublimed  in  Dejardin's,  or  other  similar  apparatus.  The  flowers  of 
sulphur,  which  first  distill  over,  are  contaminated  with  sulphur 
dioxide,  and  are  redistilled  with  a  new  portion  of  sulphur.  The 
purified  brimstone  is  finely  ground  in  ball-mills,  disintegrators,  or 
under  edge-runners,  sometimes  with  the  addition  of  a  part  of  the 
charcoal.  Bronze  balls  are  used  in  the  mill ;  the  dust  is  carefully 
sifted. 

The  nitre  is  purified  from  chloride,  or  sodium  nitrate,  by  several 
recrystallizations  from  pure  water,  the  solution  being  stirred  while 
cooling  in  order  to  separate  fine  crystals.  These  are  washed  with 
water  while  in  the  centrifugal  machine,  or  on  a  draining  platform. 
They  are  not  usually  dried  before  mixing. 

Carbon  for  gunpowder  is  best  obtained  from  charcoal  prepared 
from  light,  soft  woods,  such  as  willow,  poplar,  alder,  or  blackthorn. 
Young  trees  cut  in  the  spring  when  full  of  sap  are  preferred.  The 
bark  is  removed,  and  the  wood  stored  for  about  two  years  until 
thoroughly  dried.  It  is  then  carbonized  in  sheet-iron  cases,  which 
are  heated  in  retorts,  from  which  the  products  of  distillation  may  be 
collected  or  not,  as  desired.  The  temperature  of  the  carbonization 
depends  upon  the  kind  of  powder  to  be  made.  For  black  powder 
it  ranges  from  350°  to  500°  C. ;  for  brown  powder  it  does  not  exceed 
280°  C.  When  the  carbonization  is  ended,  the  cases  are  removed  and 
allowed  to  cool  before  they  are  opened.  The  charcoal  is  then  sorted 
to  secure  uniformity  in  the  product,  and  is  stored  for  some  time 
before  grinding,  to  allow  it  to  absorb  all  the  oxygen  possible ;  other- 
wise spontaneous  combustion  of  the  powdered  charcoal  is  liable  to 
occur. 

Charcoal  for  black  powder  contains  about  80  to  90  per  cent  car- 
bon, 5  to  7,5  per  cent  of  oxygen,  and  2  to  3  per  cent  hydrogen.  That 
for  brown  powder  contains  about  70  to  75  per  cent  of  carbon,  20  to 
25  per  cent  oxygen,  and  4.5  to  5  per  cent  of  hydrogen.  The  residue, 
in  each  case,  is  ash. 

The  ground  materials  are  weighed,  due  allowance  being  ma$e  for 
the  moisture  in  the  nitre,  and  then  put  into  the  mixing  machine; 
this  consists  of  a  gun-metal  cylinder  revolving  around  a  horizontal 
shaft,  which  turns  in  a  direction  opposite  to  that  of  the  cylinder,  and 
carries  arms  which  stir  up  the  mass  as  they  revolve.  After  mixing, 
the  "green  charge"  is  sifted  again,  moistened  with  from  5  to  6  per 
cent  of  water,  and  spread  on  the  bed  of  the  incorporating  mill.  This 
is  an  edge-runner,  having  steel  rolls,  which  travel  on  a  bed  of  bronze 
or  stone.  The  rollers  are  usually  about  15  inches  wide,  and  weigh 
3  tons  each.  They  make  7  or  8  revolutions  per  minute,  and  the 


420  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

usual  time  of  grinding  a  charge  is  from  3  to  6  hours.  Travelling 
wooden  scrapers  push  the  charge  from  the  sides  of  the  bed  into  the 
path  of  the  rollers.  The  charge  is  kept  moist  during  the  incorpo- 
rating, but  explosions,  the  causes  of  which  are  not  easy  to  discover, 
occur  frequently.  Consequently,  the  mill  is  arranged  to  run  as 
nearly  automatically  as  possible,  and  the  workmen  leave  the  build- 
ing during  this  process. 

The  "mill-cake"  coming  from  the  incorporating  mill  is  lumpy,  and 
is  reduced  to  tine  powder  by  passing  through  the  "breaking  down 
machine."  This  consists  of  two  sets  of  gun-metal  rolls,  placed  one 
over  the  other,  the  upper  set  being  corrugated  and  the  lower  pair 
smooth.  These  rolls  are  set  in  movable  bearings,  which  allow  them 
to  separate  slightly,  in  case  of  any  excessive  pressure.  The  mill- 
cake  is  thus  reduced  to  a  fine  meal,  containing  from  1  to  4  per  cent 
of  moisture.  This  is  put  into  wood-lined  metal  fiames,  or  simply 
spread  between  ebonite  plates,  and  pressed  in  an  hydraulic  press  to 
the  desired  density,  usually  300  to  450  pounds  pressure  per  square 
inch  being  applied.  The  press-cake  so  formed  may  be  as  thick  as 
desired,  for  special  purposes,  but  is  usually  about  one-half  an  inch 
thick.  For  common  powder,  this  compact,  dense  press-cake  is  put 
through  the  granulator,  which  consists  of  two  or  three  pairs  of 
grooved  or  toothed  rolls  of  gun-metal;  between  them  are  inclined 
oscillating  sieves,  which  sift  the  material  from  one  pair  of  rolls  and 
deliver  the  coarse  particles  to  the  next  pair,  where  they  are  again 
crushed.  Under  the  whole  series  of  rolls  are  two  sieves,  the  upper 
having  a  No.  10  mesh  and  the  lower  having  a  No.  20  mesh.  These 
remove  the  coarse  particles,  and  the  fine  grains  are  run  over  several 
finer  meshed  sieves,  to  obtain  various  grades  of  sporting  powder,  and 
dust.  The  grains  thus  separated  are  glazed;  i.e.  the  powder  is  placed 
in  revolving  wooden  drums,  in  which,  by  rubbing  against  each  other, 
the  sharp  corners  and  edges  are  worn  off.  Powder  which  has  been 
heavily  pressed  is  hard  and  dense,  and  takes  considerable  polish. 
For  common  grades,  it  is  customary  to  add  about  one  ounce  of  graph- 
ite to  every  100  pounds  of  powder  in  the  glazing  drum.  This  coats 
the  grains  and  fills  the  pores,  thus  protecting  them  from  moisture 
and  atmospheric  influences. 

After  glazing,  the  dust  is  removed  by  sifting,  and  the  powder  is 
dried.  It  is  spread  in  wooden  frames  having  cloth  bottoms,  and 
these  are  placed  in  racks  in  a  room  through  which  a  current  of  warm 
air  is  circulating,  and  which  is  kept  at  a  constant  temperature  of  35° 
to  60°  C.,  according  to  the  nature  of  the  powder.  The  temperature  is 
raised  slowly,  and,  after  drying,  the  powder  is  cooled  slowly,  the  en- 


EXPLOSIVES  421 

tire  process  requiring  about  24  hours.  Sometimes  the  powvler  is  dried 
in  a  stream  of  cold  air  which  has  been  passed  over  calcium  chloride, 
sulphuric  acid,  or  quicklime,  to  dry  it  before  it  enters  the  dry-room. 
Many  schemes  have  been  devised  for  drying  powder  in  vacuum,  but 
they  have  not  proved  practical. 

After  drying,  the  powder  is  given  a  final  glazing,  and  is  sifted  to 
remove  the  dust,  and  is  then  ready  for  use. 

Special  forms  of  powder  are  used  for  particular  purposes.  The 
coarse  grains  are  used  for  blasting,  the  fine  grains  for  small  arms, 
while  the  fine  dust  is  not  desirable  for  any  purpose,  except  in  fire- 
works. Pebble  and  prismatic  powders  are  chiefly  used  for  ordnance. 
The  press-cakes  of  the  "  green  charge  "  are  cut  into  pebbles,  which 
are  glazed  and  dried  like  common  powder,  but  the  drying  must  be 
slow.  For  the  prismatic  powder,  the  green  charge  is  pressed  in 
hexagonal  moulds  to  form  short  prisms,  from  f  to  If  inches  in  diame- 
ter. With  the  solid  prism  the  burning  surface  continually  dimin- 
ishes as  the  combustion  progresses,  thus  decreasing  the  rapidity  of 
the  gas  evolution.  For  use  in  heavy  ordnance,  it  is  best  that  the 
evolution  of  gas  (t.  e.  the  combustion),  shall  be  slow  at  first,  until  the 
inertia  of  the  projectile  is  overcome,  and  then  an  increasing  evolu- 
tion of  gas  is  desired.  By  perforating  the  prism  with  one  or  more 
holes  the  combustion  extends  along  the  perforations  into  the  interior, 
hollowing  out  the  grain  and  continually  increasing  the  burning  sur- 
face, with  consequent  increased  evolution  of  gas.  Thus  less  strain 
is  exerted  on  the  gun,  and  greater  velocity  imparted  to  the  ball. 
Fine  grain  powders  burn  much  more  rapidly  than  do  coarse  grain, 
and  the  strain  on  the  gun  is  proportionately  greater. 

The  United  States  army  standard  black  powder  is  composed  of:  — 

Potassium  nitrate,  75  per  cent  by  weight. 

Carbon  (as  charcoal),  15  per  cent  by  weight. 

Sulphur,-  10  per  cent  by  weight. 

The  combustion  of  this  powder  in  an  unconfined  state  may  be 
represented  as  follows  :  — 

2  KN03  +  3  C  +  S  =  3  C02  +  N2  +  K2S  .* 

But  when  exploded  in  a  confined  space  under  pressure,  the  reac- 
tion becomes  very  complex,  and  many  other  substances  are  formed. 
According  to  Debus,  t  it  is  represented  by  the  following  equa- 
tion :  — 


8  KN03  +  9C  +  3S  =  2  K2C03  +  K2S04  +  K2S2  +  7  C02  +  4  N2 

*  C.  E.  Munroe,  Rec.  U.  S.  Naval  Institute,  4,  21. 
t  Annalen  der  Chemie  und  Pharmacie,  265,  312. 


422  OUTLINES  OF   INDUSTRIAL   CHEMISTRY 

According  to  Guttmann,*  some  fifteen  products  are  formed  by 
the  free  burning  of  jpowder,  of  which  the  chief  are  potassium  sul- 
phate, potassium  carbonate,  carbon  dioxide,  nitrogen,  and  carbon 
monoxide. 

The  products  of  the  combustion  consist  of  about  57  per  cent 
solids  and  43  per  cent  gases,  by  weight.  The  pressure  exerted  by 
the  explosion  of  powder  entirely  filling  a  closed  space  is  about  44 
tons,  or  nearly  6,400  atmospheres  per  square  inch. 

Brown  or  cocoa  powder  is  much  used  for  military  purposes,  espe- 
cially for  heavy  guns.  Its  combustion  is  slower  and  smoke  less 
dense  than  with  black  powder.  It  contains  about  the  following  in- 
gredients :  — 

Potassium  nitrate 79  percent. 

Sulphur 2  to  3    «       " 

Carbonaceous  matter 18    "       " 

Moisture 0  to  1    «       " 

The  carbonaceous  matter  is  partially  charred  rye  straw,  which, 
it  is  supposed,  is  carbonized  by  exposing  it  to  superheated  steam 
until  it  takes  on  a  light  brown  (chocolate)  color.  Owing  to  incom- 
plete carbonization  of  the  straw,  the  charcoal  is  readily  combustible, 
and  can  be  used  with  a  very  small  proportion  of  sulphur. 

Mining  powders  of  several  grades  are  made  by  varying  the  pro- 
portion of  nitre,  sulphur,  and  charcoal,  according  as  a  quick  or  slow 
burning  explosive  is  desired.  These  are  generally  coarse-grained, 
and  are  cheaper  than  the  finer,  rifle  powders.  Sometimes  they  are 
made  with  sodium  nitrate  instead  of  with  potassium  nitrate,  but  this 
salt  is  somewhat  hygroscopic  and  may  absorb  sufficient  moisture  to 
damage  the  powder.  Potassium  chlorate  has  been  used  instead  of 
nitre,  but  it  is  more  expensive  and  more  dangerous  in  mixing  and 
handling,  owing  to  its  sensitiveness  to  shocks.  A  white  gunpowder 
was  formerly  made  from  potassium  chlorate,  potassium  ferrocyanide, 
and  sugar.  It  possessed  no  special  advantages  over  common  black 
powder.  The  nitrates  of  barium  and  ammonium  have  been  used  to 
replace  the  potassium  salt,  but  find  no  general  use,  owing  to  their 
greater  cost.  A  so-called  "amide  powder"  is  made  in  Germany, 
which  contains  a  large  amount  of  ammonium  nitrate  mixed  with 
potassium  nitre.  It  is  claimed  to  form  very  little  smoke. 

Gunpowder  ignites  at  about  300°  C.,  and  the  rapidity  of  combus- 
tion increases  with  the  increase  of  pressure.  Hence  the  importance 
of  a  tamping  "  in  blasting. 

*  Industrie  der  Explosivstoffe,  p.  309. 


EXPLOSIVES  423 

Nitrocellulose  or  gun-cotton  is  cellulose  hexanitrate,  C12H1404(N03)6, 
when  pure  (assuming  the  simplest  possible  formula  for  cellulose, 
n(C6H10O5),  where  n  =  2),  but  the  commercial  grades  contain  some 
lower  nitrates.  It  is  a  true  chemical  compound,  but  is  very  unstable. 
It  is  easily  made  by  dipping  clean  cotton  fibre  into  a  mixture  of 
concentrated  nitric  and  concentrated  sulphuric  acids :  — 

(C6H1005)2  +  6  HN03  -  C12HU04(NO,).  +  6  H20  * 

It  was  formerly  considered  a  true  nitro-body  with  the  formula 
C6H705  •  (N02)3,  but  it  is  now  regarded  as  a. nitrate  of  cellulose.  Its 
decomposition  on  explosion  is  represented  by  the  following  equa- 
tion :  — 

C12H1404  -  (N03)6  =  7C02  +  5CO  +  6]Sr  +  8H+3  H2O. 

The  amount  of  gas  set  free  by  the  explosion  of  one  kilogram  of 
gun-cotton,  reduced  to  0°  C.  and  760  mm.,  calculating  the  water  as 
vapor,  is  859  litres,  which  is  a  greater  volume  than  that  from  any 
other  explosive.  Since  the  amount  of  heat  liberated  by  its  decom- 
position is  1074  calories, f  the  products  of  combustion  are  entirely 
gaseous  and  enormously  expanded. 

Gun-cotton  was  discovered  by  Schoenbein  in  1846,  and  attempts 
were  made  in  several  countries  to  use  it  for  military  purposes.  But 
several  spontaneous  explosions  of  magazines  occurred,  which  soon 
caused  it  to  be  given  up.  In  1865  Abel  showed  that  these  explo- 
sions were  caused  by  the  presence  of  acid  within  the  fibre.  Cotton 
fibre  is  a  long,  hollow  tube,  much  twisted  and  shrunken,  into  which 
the  acid  penetrates  and  is  only  removed  with  great  difficulty,  if  the 
fibre  is  not  cut  and  ground  to  a  fine  pulp.  Abel  improved  the  pro- 
cess of  manufacture,  and  now  gun-cotton,  when  properly  made,  is 
considered  one  of  the  safest  of  explosives.  Owing  to  the  cost  and 
difficulty  of  its  preparation,  its  use  is  mainly  confined  to  military 
purposes  and  the  production  of  high  grade  "  smokeless  powder." 

The  cotton  used  is  "  waste  "  from  cotton  spinning,  and  contains 
dirt  and  grease,  besides  natural  gums  and  oil.  To  clean  it,  it  is 
first  given  a  "  soda  boil."  About  200  pounds  of  cotton  are  boiled  for 
eight  hours  in  a  solution  of  35  pounds  of  caustic  soda  in  250  gallons 
of  water.  The  lye  is  drawn  off  and  the  cotton  boiled  for  eight 
hours  in  clean  water,  after  which  it  is  washed  in  a  centrifugal 
machine  with  hot  water,  until  free  from  alkali.  It  is  then  spread 
on  wire  netting  and  dried  in  a  room  kept  at  180°  F.  To  remove  the 
knots  and  to  loosen  up  the  fibre,  it  is  run  through  a  "  picker  ma- 

*  Guttmann,  Industrie  der  Explosivstoffe,  318. 
t  Berthelot. 


424  OUTLINES   OF  INDUSTRIAL  CHEMISTRY 

chine,"  after  which  it  is  again  dried  for  eight  hours  at  225°  F.,  while 
a  strong  draught  is  maintained  through  the  dry-room.  The  cotton 
is  then  nitrated  in  the  "  dipping  room "  in  cast-iron  tanks,  each 
about  one  foot  deep  by  10  by  16  inches  at  the  top,  and  surrounded 
by  a  water-jacket,  through  which  cold  water  flows.  The  great 
volume  of  fume  liberated  during  the  nitrating  is  carried  away 
through  a  hood  above  each  dipping  tank.  The  acid  used  is  a 
mixture  of  one  part  concentrated  nitric  (sp.  gr.  1.50),  with. three 
parts  of  concentrated  sulphuric  (sp.  gr.  1.85).  The  dry  cotton  is 
weighed  out  in  one  pound  bunches  and  about  one-third  of  a  pound 
is  thrown  into  the  dipping  tank  at  one  time,  and  quickly  submerged 
in  the  acid  by  means  of  a  steel  fork.  When  the  whole  pound  has 
been  added,  the  mass  is  allowed  to  stand  quietly  while  the  other 
tanks  are  similarly  charged.  In  about  ten  minutes  the  cotton  is 
raked  out  of  the  acid,  and  placed  on  an  iron  grating,  against  which  it 
is  pressed  by  means  of  a  lever  carrying  a  cast-iron  plate,  the  excess 
of  acid  flowing  back  into  the  tank.  The  cotton,  still  retaining 
about  11  times  its  weight  of  acid,  is  then  placed  in  an  earthenware 
crock,  which,  is  covered  and  set  in  a  trough  of  cold  water  for  24 
hours.  During  this  period  of  digestion,  the  acid  completes  the 
conversion  of  the  cotton  into  cellulose  nitrate.  The  acid  in  the 
dipping  trough  is  replenished  and  a  new  charge  of  cotton  is 
introduced. 

The  gun-cotton  is  transferred  from  the  crock  to  a  centrifugal 
machine,  where  as  much  as  possible  of  the  spent  acid  is  thrown  off, 
and  is  generally  returned  to  the  acid  makers.  The  gun-cotton  is 
then  quickly  plunged,  in  small  quantities  at  a  time,  into  a  large  vat 
full  of  cold  water.  The  contact  of  the  strong  acid  still  in  the  cotton, 
with  the  water,  is  liable  to  generate  much  heat,  and  to  avoid  danger 
only  small  quantities  of  cotton  are  introduced  at  a  time,  and  thor- 
oughly stirred  by  a  paddle  wheel,  to  dissipate  the  acid  through  the 
large  volume  of  cold,  water  and  thus  keep  down  the  temperature. 
After  washing  in  the  vat,  the  gun-cotton  is  again  placed  in  the  cen- 
trifugal machine  and  washed  with  fresh  water.  Then  it  is  boiled 
with  dilute  sodium  carbonate  solution  for  eight  hours;  or  sometimes 
it  is  boiled  with  water  only,  for  two  or  three  days.  The  boiling  is 
done  with  steam  coils,  which  are  surrounded  with  very  fine  wire 
gauze,  at  a  distance  of  two  or  three  inches,  to  prevent  the  gun-cotton 
coming  in  contact  with  the  hot  pipes.  The  gun-cotton  is  again 
washed  in  the  centrifugal  machine  and  then  boiled  in  clear  water 
for  eight  hours,  and  the  centrifugal  washing  repeated.  It  may  then 
be  dried  at  a  temperature  not  exceeding  40°  C.,  if  it  is  to  be  used  in 


^v 

EXPLOSIVES 


loose  form.  For  military  use  and  for  smokeless  powder,  it  is  not 
dried,  but  is  put  into  a  pulping  machine  or  "  hollander,"  similar  to 
those  used  for  paper  pulp,  p.  506,  in  which  it  is  cut  and  torn,  under 
water,  into  short,  loose  fibres.  The  pulp  is  then  transferred  to  the 
washing  machine,  or  "poacher,"  which  contains  a  paddle  wheel; 
here  it  is  washed  with  pure  water  until  it  is  free  from  all  traces  of 
acid.  It  is  then  tested  with  a  mixture  of  ether  and  alcohol,  for 
soluble  cellulose  nitrates,  which  must  not  be  present.  The  contents 
of  the  poacher  are  then  mixed  with  lime-water,  precipitated  calcium 
carbonate,  and  caustic  soda  in  small  quantities,  and  is  then  drawn 
directly  into  the  moulding  presses,  where  the  excess  water  is  pressed 
out,  and  the  gun-cotton  formed  into  cakes  sufficiently  hard  to  bear 
handling.  These  are  then  pressed  heavily  in  a  hydraulic  press  to 
form  very  compact  cakes  of  the  size  and  shape  desired.  For  most 
military  purposes,  the  press-cakes  contain  from  16  to  30  per  cent 
of  moisture ;  these  will  explode  with  the  same  energy  as  when  dry, 
and  are  considered  much  safer  to  transport  and  handle.  They  are 
exploded  by  detonation  with  a  fulminate  of  mercury  cap. 

Cellulose  hexanitrate  is  insoluble  in  water,  alcohol,  ether,  and 
chloroform.  It  is  somewhat  soluble  in  acetone  and  in  ethyl  acetate, 
and  swells  to  form  a  jelly-like  mass  with  nitrobenzene.  It  resembles 
the  original  cotton  in  appearance,  but  is  slightly  harsher  to  the 
touch.  It  is  not  exploded  readily  by  shocks,  but  explodes  with  great 
violence  when  detonated.  When  unconfined,  it  burns  rapidly  with 
a  large  flame.  When  not  washed  entirely  free  from  acid,  it  is  liable 
to  spontaneous  decomposition  and  explosion. 

Lower  cellulose  nitrates  are  prepared  for  making  collodion,  cellu- 
loid, and  smokeless  powder.  These  nitrates  are  called  pyroxyline, 
and  consist  of  the  di-,  tri-,  tetra-,  and  penta-nitrates.  They  are  solu- 
ble with  greater  or  less  readiness  in  ether  and  mixtures  of  alcohol 
and  ether.  The  degree  of  solubility  depends  upon  the  strength  of 
the  acid  used,  and  the  temperature  and  time  of  the  nitrating.  Some- 
times nitre,  instead  of  nitric  acid,  is  mixed  with  the  sulphuric  acid 
in  making  pyroxyline. 

Nitroglycerine,  C3H5(N03)3,  was  discovered  in  1847,  but  no  at- 
tempt to  make  practical  use  of  it  was  made  until  about  1864,  when 
Nobel  established  a  factory  and  began  its  production  on  a  large  scale. 
But  very  soon  a  number  of  explosions  occurred  when  handling  and 
transporting  the  liquid,  and  means  were  at  once  sought  to  render  it 
less  dangerous.  In  1866  Nobel  invented  dynamite,  by  absorbing  the 
liquid  nitroglycerine  in  diatomaceous  earth,  and  this  is  now  the  form 
in  which  most  nitroglycerine  is  utilized. 


426 


OUTLINES  OF  INDUSTRIAL  CHEMISTRY 


The  name  nitroglycerine  is  a  misnomer  which  was  given  under 
the  erroneous  supposition  that  it  contained  the  nitro  group  N02,  but 
its  true  constitution  was  later  shown  to  be  glyceryl  trinitrate.  It  is 
easily  made  by  the  action  of  concentrated  nitric  acid  on  glycerine  :  — 

C3H5(OH)3  +  3  HN08  =  3  H20  +  C3H5(N08)3. 

Since  the  nitric  acid  must  be  very  concentrated  for  this  reaction,  it 
is  customary  to  mix  it  with  concentrated  sulphuric  acid ;  this  ab- 
sorbs the  water  which  is  formed  during  the  nitration  and  which 
would  otherwise  dilute  the  acid  too  much.  The  glycerine  used  is 

the  very  concentrated  dynamite  glyc- 
erine (p.  333)  of  at  least  1.262  sp.  gr. 
The  proportions  of  acid  used  are  about 
3  parts  of  nitric  acid  (93  to  95  per  cent 
HN03)  and  5  parts  .of  sulphuric  acid 
(96  per  cent  Hj,S04),  the  mixture  being 
well  cooled  before  use.  The  glycerine 
must  be  run  into  the  acid,  in  order 
that  it  may  be  nitrated  rapidly.  It 
would  be  difficult  to  thoroughly  mix 
the  acid  into  the  glycerine,  owing  to 
the  viscosity  of  the  latter,  especially 
when  cold.  Mowbray,  who  prepared 
the  nitroglycerine  for  the  Hoosac  tun- 
nel in  1868,  was  the  first  to  use  cold 

compressed  air  to  stir  the  mixture.  His  apparatus  (Fig.  91)  con- 
sists of  a  circular  wooden  trough  full  of  cold  water,  in  which  are 
earthenware  pitchers,  each  containing  17  pounds  of  mixed  acid. 
Glycerine  was  dropped  into  the  acid  from  jars  placed  on  the  shelf 
above,  while  a  blast  of  cold  air  was  introduced  by  means  of  a  glass 
tube  dipping  into  the  pitcher.  Above  the  trough  was  a  hood  to 
carry  off  the  fumes.  Much  heat  was  set  free  during  the  nitrat- 
ing, and  was  carried  away  by  the  cold  water  in  the  trough,  and 
by  the  cold  air-blast.  The  best  temperature  is  about  20°  C. ;  if  it 
goes  much  above  20°  C.,  much  fume  of  nitrogen  peroxide  is  set  free  ; 
above  30°  C.  the  reaction  becomes  dangerous,  and  the  pitcher  was  at 
once  overturned  and  the  contents  "  drowned  "  in  the  large  quantity 
of  cold  water  in  the  trough.  About  2  pounds  of  glycerine  was  ni- 
trated in  each  pitcher  at  one  charge,  and  this  required  one  and  a 
half  hours  for  its  introduction  into  the  acid.  When  nitrated,  the 
contents  of  the  pitcher  was  poured  into  a  large  vat  of  cold  water ; 
the  nitroglycerine  sunk  to  the  bottom  and  the  acid  water  was  drawn 


FIG.  91. 


EXPLOSIVES  427 

off.  After  several  washings  with  water,  and  finally  with  a  sodium 
carbonate  solution,  the  explosive  was  ready  for  use. 

By  more  recent  methods,  the  entire  amount  of  acid  is  mixed  and 
placed  in  one  vat,  and  several  hundred  pounds  of  the  glycerine  is 
introduced  in  numerous  fine  streams  from  a  perforated  pipe,  or  as  a 
fine  spray  by  means  of  an  injector  with  a  blast  of  air.  A  coil  for' 
the  circulation  of  cold  water  is  placed  in  the  vat,  and  several  air 
pipes  are  provided,  through  which  cold  compressed  air  is  forced  into 
the  mixture.  The  vat  is  covered  and  a  pipe  carries  the  fumes  to  the 
chimney.  The  temperature  of  the  reaction  is  determined  by  a  ther- 
mometer, and  is  regulated  by  the  rate  of  inflow  of  the  acid  and  by 
the  use  of  the  compressed  air  agitators.  After  the  reaction  is  over, 
the  entire  mass  is  drawn  into  the  separator  tank ;  in  about  30 
minutes  the  nitroglycerine  has  risen  to  the  top,  if  pure  materials 
have  been  used,  and  is  drawn  off  by  a  special  cock  above  the  acid, 
and  is  run  at  once  into  a  tank  containing  water  at  15°  C. ;  colder 
water  might  cause  it  to  freeze.  The  temperature  is  watched  care- 
fully, and  must  not  rise  above  30°  C.  The  product  is  washed  several 
times  in  water  and  then  with  a  sodium  carbonate  solution,  to  remove 
all  traces  of  acid. 

In  order  to  have  a  better  control  of  the  nitration,  Boutmy  and 
Faucher  proposed  to  mix  the  glycerine  with  part  of  the  sulphuric 
acid,  and  to  cool  the  resulting  sulphoglyceric  acid,  C3H5(OH)2(HS04), 
or  CaH5(HS04)3.  Then  to  mix  the  nitric  with  the  remainder  of  the 
sulphuric  acid,  cool,  and  to  add  the  sulphoglyceric  acid ;  it  is  thus 
nitrated  to  form  the  nitroglycerine,  but  much  less  heat  is  evolved 
than  when  nitrating  the  glycerine  directly.  But  on  trial  of  the 
process,  several  serious  explosions  occurred  which  were  not  clearly 
explained,  and  it  has  been  generally  abandoned. 

On  explosion,  the  nitroglycerine  decomposes  about  as  follows :  — 

2  C3H5(N03)3  =  6  CO,  +  6  N  +  5  H,0  +  0. 

The  volume  of  gas  at  100°  C.  thus  produced  is  about  six  times  as 
great  as  from  gunpowder,  and  the  actual  temperature  of  the  explo- 
sion is  much  higher  than  that  of  gunpowder,- being  about  3000°  C.  as 
calculated  by  Wuic  (quoted  by  Guttmann).  The  volume  of  gas  pro- 
duced by  one  litre  of  nitroglycerine  is  about  1135  litres.  According 
to  Ost,*  the  temperature  of  the  explosion,  as  calculated  from  the 
observed  heat  of  the  explosion  and  the  specific  heat  of  the  products 
of  the  combustion,  is  6980°  C.  The  volume  of  gas  reduced  to  0°  and 
760  mm.  from  one  kilo  of  nitroglycerine  is  713  litres,  but  at  6980°  C. 

*  Lehrbuch  der  technischen  Chemie,  158. 


428  OUTLINES   OF  INDUSTRIAL  CHEMISTRY 


the  volume  is  18,966  litres  [713  x  (1  -f  -^W)]  and  tlie  pressure  is 
about  31,367  kilograms  per  square  centimeter. 

Nitroglycerine  is  a  heavy  oily  liquid  of  a  pale  yellow  color  and 
sweet  taste.  Its  specific  gravity  is  1.60.  It  is  insoluble  in  water,  but 
dissolves  in  ether,  benzene,  methyl  alcohol,  and  chloroform.  It  freezes 
at  about  8°  C.  and  thaws  at  about  12°  C  ,  though  there  is  some  varia- 
tion in  these  points  in  different  samples,  according  to  their  purity. 
It  explodes  when  heated  to  180°  C.,  but  burns  in  the  open  air  without 
explosion,  if  in  small  quantities.  It  is  very  sensitive  to  shocks  and 
may  readily  be  detonated  by  a  sharp  blow.  "When  pure,  it  keeps 
indefinitely  in  a  dark  place,  but  exposure  to  sunlight  increases  its 
sensitiveness  and  may  cause  spontaneous  explosion.  Taken  inter- 
nally, it  is  very  poisonous  and  is  a  powerful  medicinal  agent,  some- 
what resembling  strychnine  in  its  physiological  effects  ;  ten  grains 
are  said  to  be  a  fatal  dose,  while  smaller  quantities  cause  headache 
and  vertigo  ;  even  when  only  in  contact  with  the  skin,  it  is  said  to 
cause  violent  headache.  It  is  used  as  a  remedy  in  angina  pectoris, 
and  is  injected  into  the  blood  in  cases  of  poisoning  by  carbon  monox- 
ide, or  water-gas. 

As  an  explosive,  it  is  only  used  in  the  liquid  state  for  "  torpe- 
doing" oil  and  gas  wells  (p.  289).  When  frozen,  it  is  much  less 
sensitive  to  shocks,  and  may  be  transported  and  handled  with  safety. 
But  before  use,  it  should  be  thawed  by  standing  in  a  room  warmed 
to  about  20°  C.  It  is  one  of  the  ingredients  of  a  large  number  of 
high  explosives  which,  although  not  so  powerful  as  the  nitro- 
glycerine itself,  are  much  safer  and  more  convenient  to  handle. 
These  explosives  may  be  divided  into  two  classes:  (a)  those  in 
which  the  nitroglycerine  is  absorbed  in  some  inert,  non-explosive 
material,  and  (ft)  those  in  which  it  is  mixed  or  combined  with  sub- 
stances which  are  in  themselves  explosive.  The  most  important 
example  of  the  first  class  is  dynamite  ;  in  this  the  nitroglycerine  is 
absorbed  in  infusorial  earth,  white  clay,  pulverized  mica,  sawdust, 
or  powdered  charcoal.  The  chief  requisite  of  a  good  absorbent  or 
"  dope  "  is  that  it  shall  hold  the  nitroglycerine  without  any  oozing 
or  dripping,  otherwise  the  liquid  spreads  in  thin  films  over  the  out- 
side of  the  package,  and  becomes  extremely  sensitive  to  shocks,  and 
very  dangerous.  Infusorial  earth,  often  known  by  its  German 
name,  Kieselguhr.  is  generally  used  as  an  absorbent.  This  consists 
of  a  white  clay,  containing  a  large  amount  of  the  frustrates  of 
diatom  es,  which  are  chiefly  minute  tubes,  into  which  the  nitro- 
glycerine is  drawn  by  capillary  attraction,  and  permanently  held. 
The  kieselguhr  is  calcined  to  dry  it,  and  to  destroy  organic  matter, 


EXPLOSIVES  429 

and  is  then  mixed  by  hand  with  the  requisite  amount  of  nitro- 
glycerine and  a  little  calcined  soda,  to  destroy  any  acidity.  With 
three  parts  of  nitroglycerine  to  one  of  kieselguhr,  the  dynamite  is 
plastic,  and  contains  75  per  cent  of  its  weight  of  nitroglycerine. 
This  is  usually  called  dynamite  No.  1,  or  giant  powder.  It  is  packed 
into  tubes  of  paraffined  paper,  and  compressed  by  hand  to  form  car- 
tridges of  the  desired  weight.  It  is  not  very  sensitive  to  shocks,  but 
is  readily  detonated  by  an  explosive  cap.  In  cold  weather  the  nitro- 
glycerine congeals,  and  such  frozen  dynamite  does  not  yield  good 
results.  It  is  best  thawed  by  placing  in  a  warm  room  for  some 
time  before  use.  It  should  never  be  placed  near  a  stove  or  fire, 
since  it  is  almost  certain  to  explode  if  heated  to  180°  C.  Dynamite 
is  also  made  with  50,  30,  or  even  10  per  cent  of  nitroglycerine,  and 
used  where  the  No.  1  grade  would  cause  too  much  shattering. 

Mica  powder  consists  of  powdered  mica,  in  which  about  50  per 
cent  of  nitroglycerine  is  absorbed.  The  other  explosives  with  inert 
dope  are  not  now  important. 

A  great  number  of  explosives  with  an  active  dope  are  on  the 
market.  Most  of  them  consist  of  mixtures  of  sulphur,  sodium  or 
potassium  nitrate,  powdered  charcoal,  wood  fibre  or  other  carbo- 
naceous matter,  impregnated  with  nitroglycerine.  These  are  sold 
under  various  fancy  names,  such  as  Vulcan,  Hercules,  Judson,  Atlas, 
and  Hecla  powders,  and  lithofracteur  carbonite,  stonite,  vigorite,  etc. 
As  typical  examples  of  these  explosives,  the  following  will 
serve :  — 

ATLAS   POWDER 

GRADE  A.  GRADE  B. 

Sodium  nitrate 2  34 

Wood  fibre 21  14 

Magnesium  carbonate    .....  2  2 

Nitroglycerine 75  50 

JUDSON   POWDER 

Sodium  nitrate 64 

Sulphur 16 

Cannel  coal • 15 

Nitroglycerine 5 

FORCITE 

Potassium  nitrate 18 

Gelatinized  cotton 7 

Nitroglycerine 75 


430  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

Forcite  is  a  plastic  mass,  resembling  rubber,  impervious  to  water, 
and  safe  to  handle.  It  is  made  by  treating  finely  pulped  cotton 
with  high  pressure  steam  until  the  whole  mass  is  converted  into  a 
jelly,  which  is  then  mixed  with  nitroglycerine  at  a  temperature  of 
40°  C.,  and  powdered  nitre  is  then  added. 

Nitrogelatine  or  blasting  gelatine  is  made  by  dissolving  soluble 
nitrated  cellulose  (collodion)  in  nitroglycerine.  The  latter  is  warmed 
to  about  35°  C.,  and  the  collodion  slowly  stirred  in,  until  7  or  8  per 
cent  has  been  added.  After  a  time  the  mass  becomes  viscous,  and  is 
formed  into  cartridges.  It  is  not  very  sensitive  to  shocks,  and  may 
be  made  less  so  by  adding  3  or  4  per  cent  of  camphor.  It  is  not 
affected  by  water  and  hence  may  be  used  for  submarine  work.  It 
keeps  well  when  stored,  and  is  a  more  powerful  explosive  than 
dynamite. 

Gelatine  dynamite  consists  of  blasting  gelatine,  mixed  with  wood 
pulp  (4-J-  per  cent)  and  potassium  nitrate  (26  per  cent),  together 
with  a  little  sodium. carbonate. 

An  explosive  somewhat  similar  to  blasting  gelatine  is  cordite, 
a  "smokeless  powder,"  which  has  been  adopted  by  the  English  gov- 
ernment as  a  military  explosive.  This  was  patented  by  Abel  and 
Dewar,  and  consists  of:  — 

Nitroglycerine 58     parts. 

Gun-cotton 37         " 

Vaseline 5         " 

Acetone 19.2      « 

The  nitroglycerine  and  gun-cotton  are  mixed  by  hand,  the 
acetone  is  added,  and  the  paste  worked  in  a  kneading  machine 
for  3^-  hours.  The  vaseline  is  then  added,  and  the  whole  kneaded 
for  3  hours  more.  The  paste  is  then  forced  through  a  spaghetti 
machine  to  form  threads,  which  are  wound  on  drums  and  dried  at 
40°  C.  for  several  days  to  evaporate  off  the  acetone.  The  threads  are 
then  cut  into  convenient  lengths  for  use  in  cartridges. 

Smokeless  powders  are  now  very  important  for  military  and 
sporting  purposes.  They  are  probably  too  expensive  for  blasting 
and  mining.  The  base  of  these  powders  is  nitrated  cellulose,  which 
has  been  treated  in  various  ways  to  render  it  slower  in  burning  than 
gun-cotton,  and  also  less  sensitive  to  heat  and  shocks.  As  a  rule, 
they  are  less  inflammable  than  gun-cotton,  and  require  stronger  deto- 
nators. Since  metallic  salts  cause  smoke,  they  are  not  used  in  these 
powders.  There  are  three  general  classes  of  smokeless  powders  now 
in  use :  (a)  Those  consisting  of  mixtures  of  nitroglycerine  and 


EXPLOSIVES  431 

nitrated  cellulose,  which  have  been  converted  into  a  hard,  horn-like 
mass,  either  with  or  without  the  aid  of  a  solvent.  To  this  group 
belongs  ballistite,  containing  50  per  cent  nitroglycerine,  49  per  cent 
nitrated  cellulose  (collodion),  and  1  per  cent  diphenylamine ;  also, 
cordite  (see  above),  Leonard's  powder  and  amberite.  This  last  con- 
tains 40  parts  nitroglycerine  and  56  parts  nitrated  cellulose.  (6)  Those 
consisting  mainly  of  nitrated  cellulose  of  any  kind,  which  has  been 
rendered  hard  and  horny  by  treatment  with  some  solvent,  which  is 
afterwards  evaporated.  These  are  prepared  by  treating  nitrated 
cellulose  with  ether  or  benzene,  which  dissolves  the  collodion,  and 
when  evaporated  leaves  a  hard  film  of  collodion  on  the  surface  of 
each  grain.  Sometimes  a  little  camphor  is  added  to  the  solvent,  and, 
remaining  in  the  powder,  greatly  retards  its  combustion,  (c)  Those 
consisting  of  nitro-derivatives  of  the  aromatic  hydrocarbons,  either 
with  or  without  the  admixture  of  nitrated  cellulose ;  to  this  group 
belong  Dupont's  powder,  consisting  of  nitrated  cellulose  dissolved  in 
nitrobenzene  ;  indurite,  consisting  of  cellulose  hexanitrate  (freed  from 
collodion  by  extraction  with  methyl  alcohol)  made  into  a  paste  with 
nitrobenzene,  and  hardened  by  treatment  with  steam  until  the  excess 
of  nitrobenzene  is  removed ;  and  plastomenite,  consisting  of  dinitro- 
toluene  and  nitrated  wood  pulp. 

Another  class  of  explosives  which  are  not,  however,  employed  to 
any  extent,  are  the  picrates  and  picric  acid.  By  treating  phenol, 
C,jH5  •  OH,  with  concentrated  nitric  acid,  tri-nitrophenol  or  picric 
acid,  C6H2(OH)  -  (N0,)3,  is  formed.  The  alkaline  salts  of  this  body 
(called  picrates)  are  powerful  explosives.  Ammonium  picrate  mixed 
with  potassium  nitrate  has  been  proposed  as  a  military  explosive. 

Melinite  is  a  mixture  of  picric  acid  with  collodion,  or  in  one  form 
is  supposed  to  be  fused  picric  acid  alone,  which  has  been  melted  in  a 
carefully  regulated  oil-bath.  It  was  tested  in  France  for  a  military 
explosive  for  shells,  but  was  found  to  attack  the  metal  of  the  shell. 

The  salts  of  fulminic  acid,  C2H202N2,  called  fulminates,  are  ex- 
ceedingly dangerous,  being  very  easily  exploded  by  shocks  or  blows. 
The  silver  and  mercury  fulminates  are  the  most  important.  The 
former  is  too  dangerous  for  general  use,  but  the  latter  is  largely 
used  as  the  "  primer  "  in  percussion  caps.  It  is  made  by  mixing 
a  solution  of  mercuric  nitrate  and  nitric  acid  with  alcohol.  It  is  a 
very  dangerous  explosive  when  dry. 

In  order  to  avoid  danger  in  shipping  and  handling,  a  class  of 
explosives  has  come  into  use  in  which  the  ingredients,  in  themselves 
non-explosive,  are  mixed  immediately  before  use.  These  are  called 


432  OUTLINES  OF   INDUSTRIAL  CHEMISTRY 

Sprengel  explosives,  from  the  name  of  the  inventor ;  they  are  very 
powerful  in  many  cases,  and  some  of  them  are  extensively  used. 
Roburite  consists  of  dinitrochlorbenzene,  cr  possibly  dinitrobenzene 
alone,  mixed  with  ammonium  nitrate.  It  does  not  explode  by  fric- 
tion or  shock,  but  is  readily  detonated.  It  yields  hydrochloric  acid 
in  the  combustion  gases,  and  hence  is  disadvantageous  in  mining. 
Bellite  and  securite  are  somewhat  similar  to  roburite.  Romite  con- 
tains nitronaphthalene,  paraffine,  potassium  chlorate,  and  ammonium 
nitrate,  in  various  proportions.  Ammonite  contains  nitronaphthalenes 
and  ammonium  nitrate.  Rack-a-rock  is  made  from  potassium  chlo- 
rate soaked  in  nitro  benzene,  or  in  the  "  dead  oil "  from  tar.  It  is 
very  powerful,  and  moderate  in  price.  It  was  largely  used  in  the 
removal  of  Hell  Gate  in  New  York  Harbor.  Panclastite  is  a  liquid 
consisting  of  carbon  disulphide  with  liquid  nitrogen  peroxide. 
Hellhoffite  consists  of  nitro-  and  dinitro-benzenes  dissolved  in  nitric 
acid. 

In  coal  mines,  especially  where  "fire  damp"  is  prevalent,  lime 
cartridges  are  sometimes  used.  These  are  made  by  compressing 
quicklime  into  cylinders,  leaving  a  small  hole  down  the  middle. 
They  are  put  into  drill  holes,  and  tamped  with  sand.  Water  is 
poured  into  the  hole,  and,  passing  into  the  perforated  cylinder,  wets 
the  lime,  which  swells  greatly  on  slaking,  and  exerts  great  pressure. 
The  coal  is  broken  down  without  any  flame  or  concussion,  and  hence 
there  is  no  danger  from  the  gas. 


REFERENCES 

Tri-Nitroglycerine  as  applied  in  the  Hoosac  Tunnel.     Geo.  M.  Mowbray,  New 

York,  1874.     (Van  Nostrand.) 

Notes  on  Certain  Explosive  Agents.     Walter  N.  Hill,  Boston,  1875. 
Researches  in  Explosives.     Captain  Noble  and  E.  A.  Abel. 

Part  I.     Fired  Gunpowder.     London,  1875. 

Part  II.     Fired  Gunpowder.     London,  1880. 
Dynamite,  ihre  okonomische  Bedeutung  und  ihre  Gefahrlichkeit.    Isador  Trauzl, 

Wien,  1876. 

Coton-poudre,  nitroglycerine  et  dynamites.     M.  Pellet,  Paris,  1881. 
Zur  la  Force  des  Matieres  explosives  d'apres  la  Thermochimie.     M.  Berthelot. 

2  Vols.     Paris,  1883. 

Die  neuen  Sprengstoffe.     Isador  Trauzl,  Wien,  1885. 
Les  Explosifs  modern es.    Paul  F.  Chalons,  Paris,  1886. 
Manuel  du  Dynamiteur.     La  Dynamite  de  Guerre  et  le  Coton-poudre.    M. 

Dumas-Giulin,  Paris,  1887. 
A  Dictionary  of  Explosives.     J.  P.  Cundill,  London,  1889. 


TEXTILE  INDUSTRIES  433 

A   Handbook  on   Modern  Explosives.     M.    Eissler,  London,  1890.     (Crosby, 

Lockwood,  &  Son.) 

Die  gepresste  Schiesswolle.     Franz  Plach,  Pola,  1891.     (E.  Scharff.) 
Explosives  and  Ordnance  Material,  etc.     Stephen  H.  Emmons.     Keprint  from. 

Vol.  17,  Proc.  U.  S.  Naval  Institute,  Baltimore,  1891. 

The  Dangers  in  the  Manufacture  of  Explosives.    Oscar  Guttmann,  London,  1892. 
Blasting.     Oscar  Guttinan,  London,  1892. 

Les  Explosifs  industriels.     J.  Daniel,  Paris,  1^93.     (Bernard  et  Cie.) 
Index  to  the  Literature  of  Explosives.     Chas.  E.  Munroe,  Baltimore,  1893. 
Die  Industrie  der  Explosivstoffe.     Oscar  Guttmann,  Braunschweig,  1895.    (Vie- 

weg  u.  Sohn.) 

Die  Explosiven  Stoffe.    Franz  Boeckmann.    2"  Auf.    Wien,  1895.    (Hartleben.) 
Journal  of  the  Society  of  Chemical  Industry  :  — 

1890,  265.     Geo.  McRoberts.     Blasting  Gelatine. 

1890,  476.     Geo.  McRoberts.     Blasting  Gelatine. 


TEXTILE  INDUSTRIES 

FIBRES 

Textile  fibres  are  divided,  according  to  their  source,  into  vege- 
table, animal,  and  mineral.  Of  these  only  the  first  two  will  be 
considered  here,  since  mineral  fibres,  consisting  of  asbestos,  slag- 
wool,  glass-wool,  metallic  wires,  etc.,  are  never  subjected  to  any  of 
the  processes  of  bleaching,  dyeing,  or  chemical  treatment  which 
come  within  the  scope  of  this  book,  though  they  are  sometimes  used 
for  packing,  lagging,  or  filtering  purposes  in  chemical  works. 

Vegetable  fibres  are  plant  cells  of  rather  simple  structure,  usually 
forming  a  part  of  the  plant  itself.  They  are  capable  of  withstanding 
high  heat,  and  are  not  readily  attacked  by  dilute  alkalies  to  cause 
disintegration  or  weakening.  They  consist  essentially  of  cellulose 
(C6H1005)/;,  which  may  be  very  pure,  or  mixed  with  its  alteration 
products ;  in  a  few  instances,  the  fibre  as  actually  employed  consists 
entirely  of  cellulose  derivatives  obtained  by  chemical  means.  Con- 
centrated caustic  alkalies  form  alteration  products  with  vegetable 
fibre  ;  free  sulphuric,  or  hydrochloric  acid,  if  strong,  quickly  destroys 
the  fibre,  but  nitric  acid  forms  nitrates,  or  oxidized  derivatives. 

Animal  fibres  are  essentially  nitrogenous  substances  (protein 
matter)  often  containing  sulphur.  They  may  consist  of  complex 
cell  structures,  or  bundles  of  cells  enclosed  in  a  single  envelope,  or 
they  are  solid  filaments  formed  from  a  liquid  secreted  by  caterpillars, 
spiders,  or  certain  mollusks.  They  are  readily  destroyed  by  hot  alka- 
lies, but  withstand  the  action  of  mineral  acids  very  well.  They  are 
much  more  easily  injured  by  dry  heat  than  are  the  vegetable  fibres. 

2F 


434 


OUTLINES  OF  INDUSTRIAL   CHEMISTRY 


VEGETABLE  FIBRES 

Vegetable  fibres  are  divided  into  two  groups,  —  seed  hairs,  con- 
sisting of  single  cells,  and  bast  fibres,  consisting  of  bundles  of  fibre- 
cells  joined  together  to  form  filaments  of  greater  or  less  length. 
The  most  important  vegetable  fibres  are  cotton,  flax  (linen),  hemp, 
jute,  China  grass,  and  esparto. 

Cotton  fibre  consists  of  the  seed  hairs  of  several  species  of  Gos- 
sypium,  plants  belonging  to  the  Malvacece,  or  mallow  family.  The 
most  important  commercial  varieties  are  Gossypium  barbadense,  L. 
(Sea  Island  cotton),  G.  herbaceum,  L.,  or  G.  hirsutum,  L.  (upland 
cotton  of  the  southern  states),  G.  arboreum,  L.  (Indian  and  Egyptian), 
and  G.  Peruvianum,  Cav.  (Brazil,  Peru,  and  neighboring  countries). 
The  varieties  are  distinguished  by  difference  in  the  length  and  fine- 
ness of  the  fibre  or  staple.  The  following  table  *  shows  the  average 
length  and  diameter  in  inches  of  the  principal  commercial  grades  :  — 


Sea  Island  

LENGTH  OF  STAPLK. 

DIAMETER 
OF  STAPLE. 

Max. 

Min. 

Average. 

1.80 
1.60 
1.06 
1.52 
1.31 
1.02 

1.41 

.88 
.81 
1.30 
1.03 

.77 

1.61 

1.02 
.93 
1.41 
1.17 

.89 

.000640 
.000775 
.000763 
.000655 
.000790 
.000844 

Upland.                      

Egyptian       

Indian                   

Thus  it  will  be  seen  that  the  longest  fibres  have  the  least  diam- 
eter ;  they  are  also  silkier,  and  can  be  spun  into  the  finest  threads. 

The  fibres  are  attached  thickly  to  the  surface  of  the  seed,  and  as 
they  develop  a  mass  of  lint  is  formed  which  ultimately  bursts  the 
enclosing  pod  or  boll.  Each  fibre  consists  of  a  single  long  cell ;  but 
as  it  grows  the  cell  walls  become  thinner,  and  finally  collapse  to 
form  arfl'at  tube.  After  the  boll  bursts  the  liquid  cell  content  solidi- 
fies by  exposure  to  the  sun  and  air,  the  dissolved  matters  are  depos- 
ited somewhat  irregularly  on  the  different  parts  of  the  cell  wall, 
and,  consequently,  the  fibre  twists  into  a  spiral  shape.  Thus,  as  seen 
under  the  microscope,  cotton  fibre  appears  as  an  irregular,  twisted, 
and  flattened  tube,  tapering  to  a  point  at  one  end.  The  unripe  fibres 
are  comparatively  straight,  but  if  made  into  yarn  they  twist  and 

*  Walter  H.  Evans,  Bulletin  No.  33,  U.  S.  Dept.  of  Agriculture,  p.  77. 


TEXTILE  INDUSTRIES  435 

curl,  and  are  of  little  value ;  being  difficult  to  dye,  they  cause  specks 
in  the  dyed  goods. 

Cotton  fibre  consists  essentially  of  cellulose  enclosed  in  a  film  or 
outside  skin  of  modified  cellulose.  On  the  surface  is  a  deposit  of 
wax  and  oily  matter  which  protect  it  from  the  action  of  moisture, 
.and  which  is  removed  in  the  bleaching  process  before  dyeing  or 
printing  the  cotton  goods.  The  cellulose  of  the  fibre  is  scarcely 
affected  by  cold  dilute  mineral  acids,  but  if  allowed  to  dry  on  the 
fibre  the  acid  quickly  attacks  it.  Concentrated  sulphuric  acid  con- 
verts cotton  into  a  gelatinous  mass,  from  which  water  precipitates  a 
starch-like  body  called  amyloid.*  By  longer  action  of  the  strong 
acid,  cotton  is  converted  into  a  soluble  compound  (cellulose  sulphuric 
acid),  then  into  dextrin,  and  finally  into  dextrose. 

Boiling  in  dilute  alkalies  has  no  injurious  action  on  cotton  if  the 
air  is  excluded;  otherwise  there  may  be  more  or  less  formation  of 
oxycellulose  which  may  weaken  the  fibre.  When  treated  with 
caustic  soda  solution  at  50°  T\v.,  the  fibre  becomes  rounded,  swollen, 
and  semi-transparent,  and  the  interior  cavity  almost  disappears,  while 
a  marked  shrinkage  in  length  takes  place.  It  gains  in  weight  and 
in  strength,  while  its  affinity  for  coloring  matter  is  much  increased. 
The  fibre  probably  enters  into  combination  with  the  alkali  to  form  a 
compound  of  the  formula  C^H^O^  •  N%O,  which  decomposes  with 
water  to  form  hydrocellulose,  C^H^O^  •  H20.  This  action  was  dis- 
covered by  John  Mercer,  hence  the  name  "mercerized  cotton"  applied 
to  fibre  which  has  been  so  treated. f 

Flax  or  linen  is  the  bast  fibre  of  the  flax  plant,  Linum  usitatissi- 
mum,  L.  The  individual  fibres  are  long  cylindrical  cells,  pointed  at 
the  ends,  and  having  thick  walls  with  a  narrow  central  cavity.  Each 
fibre  is  marked  with  transverse  bands,  and  has  a  glistening  surface. 
The  average  length  is  from  2  to  4  cm. ;  the  individual  cells  are 
united  in  bundles,  firmly  glued  together,  consequently  linen  is  much 
less  elastic  than  cotton  fibre,  next  to  which  it  ranks  in  importance 
among  vegetable  fibres.  In  warm  countries  flax  is  raised  chiefly  for 
the  seed.  (See  Linseed  Oil,  p.  308.)  That  grown  in  temperate  cli- 
mates has  much  the  better  fibre.  It  is  pulled  up  by  the  roots  before 

*  Parchment  paper  is  produced  by  the  short  action  of  strong  acid  on  paper 
whereby  a  layer  of  amyloid  is  formed  on  the  surface. 

t  The  process  has  recently  been  further  developed  for  the  production  of  a  silky 
lustre  on  cotton  goods.  The  yarn  is  mercerized  while  tightly  stretched  on  a  frame,  and 
is  washed  and  dried  in  this  state  of  tension.  This  prevents,  to  a  great  measure,  the 
shrinkage  which  would  otherwise  occur,  and  gives  a  high  lustre  to  the  fibre,  especially 
noticeable  in  the  dyed  goods.  Such  mercerized  cottons  are  now  made  to  imitate  silks. 


436  OUTLINES   OF  INDUSTRIAL   CHEMISTRY 

the  seeds  ripen,  and  is  immediately  subjected  to  the  process  of 
"rippling,"  i.e.  it  is  drawn  through  the  teeth  of  a  coarse  comb  to 
detach  the  seeds.  To  separate  the  bast  fibre  from  the  rind,  woody 
tissue,  and  pith,  the  flax  is  "retted."  This  may  be  done  in  five 
different  ways :  — 

(a)  Eetting  in  stagnant  water  is  practised  in  Ireland  and  to  some 
extent  in  Russia.  The  flax  is  put  into  pools  of  soft  water  and  left 
until  fermentation  sets  in;  this  softens  and  partly  destroys  the 
gummy  and  resinous  matter  cementing  the  fibres  to  the  ligneous 
tissue.  Great  care  is  necessary  that  the  bast  fibres  themselves  are 
not  attacked.  The  fermentation  is  often  very  offensive.  When  it 
has  gone  far  enough,  the  flax  is  exposed  to  the  action  of  the  air  and 
sunlight  for  several  days  ("grassed"). 

(b)  Ketting  in  running  water  is  extensively  practised  in  France 
and  Belgium.     The  flax  is  put  into  crates  and  submerged  in  streams. 
The  fermentation  takes  place  as  above,  but  requires  a  longer  time. 
The  coloring  matter  is  washed  away,  and  a  lighter  colored  product 
is  obtained. 

(c)  Dew  retting  consists  in  exposing  the  damp  flax  to  the  weather 
for  several  weeks.     The  fermentation  takes  place  much  as  above. 

(d)  Eetting  in  water  at  30°  to  35°  C.   hastens  the  fermentation 
greatly,  so  that  it  is  generally  complete  in  about  three  days.     The 
flax  is  often  passed  between  squeeze  rolls,  to  assist  in  detaching  the 
woody  fibre.     By  treating  the   flax  with  water   and   steam   under 
pressure,  it  is  rapidly  retted,  and  the  fibre  has  a  silky  lustre. 

(e)  Mineral  acids  are  sometimes  used  in  stagnant  water  retting, 
to  prevent  the  offensive  odor.     By  digesting  the  flax  in  very  dilute 
hydrochloric  acid,  followed  by  a  weak  alkali  bath,  the  retting  is 
quickly  finished. 

Various  mechanical  processes  are  employed  to  detach  the  ligneous 
matter  from  the  fibre  after  retting.  Breaking  consists  in  crushing 
the  flax  with  grooved  rolls;  after  this  it  is  "scutched,"  i.e.  the 
crushed  mass  is  pounded  by  hand  in  a  machine,  to  remove  the  loos- 
ened matter.  Heckling  is  a  combing  process  to  draw  the  fibres 
parallel  and  make  them  suitable  for  spinning. 

Linen  fibre  is  not  so  pure  cellulose  as  cotton,  but,  in  general,  acts 
like  the  latter.  It  is  stronger,  has  more  natural  lustre,  is  more  diffi- 
cult to  bleach  and  dye,  and,  being  a  better  conductor  of  heat,  feels 
cold  to  the  touch. 

Hemp  is  the  bast  fibre  of  Cannabis  sativa,  L.,  which  is  largely 
cultivated  in  Eussia  and  Italy.  The  fibres  are  separated  from  the 


TEXTILE  INDUSTRIES  437 

wood  and  pith  of  the  stalks  in  the  same  general  way  as  flax.  They 
are  stronger  and  coarser  than  flax,  and,  being  more  deeply  colored, 
are  mainly  used  for  rope,  coarse  canvas,  and  bagging. 

Jute  is  the  bast  fibre  of  several  species  of  Corchorus,  of  which 
C.  capsularis,  L.,  is  the  most  important.  The  plants  are  indigenous 
to  India,  and  their  cultivation  is  mainly  confined  to  India  and  Cey- 
lon, though  some  has  been  raised  in  Louisiana  and  Mississippi.  The 
fibre  is  obtained  very  pure  by  simple  retting  in  water.  It  is  very 
long,  sometimes  reaching  two  meters,  but  the  fibre  cells  are  very 
short,  and  the  filaments  are  not  so  strong  as  those  of  flax  or  hemp. 
The  fibre  is  light  yellow,  and  has,  a  high  lustre.  It  is  quite  suscepti- 
ble to  the  action  of  acids  and  alkalies,  and  is  easily/destroyed  by  min- 
eral acids.  It  cannot  be  bleached  with  bleaching  powder,  since  the 
chlorine  combines  with  the  jute.  Sodium  hypochlorite  in  weak  solu- 
tion, or  potassium  permanganate,  followed  by  sulphurous  acid,  may 
be  used  to  bleach  it.  It  differs  in  its  chemical  composition  from 
cotton  and  flax.  Its  cellulose  is  all  combined  with  lignified  tissue, 
forming  bastose.  Jute  resembles  cotton  which  has  been  mordanted 
with  tannin,  and  can  be  dyed  directly  with  basic  dyes. 

China  grass,  or  ramie,  is  a  bast  fibre  derived  from  Boehmeria 
nivea,  Gaud.,  a  species  of  nettle  cultivated  in  China  and  Eastern 
Asia.  The  fibre  is  difficult  to  detach  from  the  ligneous  matter ;  ret- 
ting usually  divides  it  into  its  component  cells,  which  cannot  then 
be  separated  from  the  stem  and  bark.  It  is  customary  to  separate 
the  fibres  by  crushing  the  green  stalk  and  washing  away  the  woody 
matter  with  running  water,  but  this  method  is  expensive.  The  fibre 
has  a  brilliant  lustre  (which  dyeing  is  liable  to  injure),  and  is  easily 
bleached.  It  is  very  strong,  and  is  nearly  pure  cellulose. 

Esparto  is  a  grass  with  tough  fibre,  cultivated  in  Spain,  and  chiefly 
used  for  cordage  and  paper  making. 

Manilla  hemp  and  sisal  are  used  as  substitutes  for  hemp.  The 
former  is  obtained  in  the  Philippine  Islands,  from  the  leaves  of  a 
wild  plantain,  Musa  textilis,  Nee.,  and,  being  tough  and  light,  is  much 
used  for  cordage  and  ropes.  Sisal  is  obtained  from  an  agave  plant, 
Agave  rigida,  Mill.,  and  A.  Americana,  L.,  in  Central  America  and 
the  West  Indies.  It  is  chiefly  used  for  burlap  as  a  substitute  for 
jute. 

Other  vegetable  fibres  of  small  importance  are  eocoanut  fibre,  from 
the  husk  of  the  eocoanut,  used  for  brushes,  mats,  and  cordage;  New 
Zealand  flax,  a  long  fibre  prepared  from  a  New  Zealand  plant,  Phor- 
mium  tenax,  Forst.,  and  chiefly  used  for  ropes;  Sunn  hemp,  an  Indian 
plant,  furnishes  a  fibre  suitable  for  ropes  and  cordage. 


438  OUTLINES  OF   INDUSTRIAL   CHEMISTRY 


ANIMAL   FIBRES 

Of  animal  fibres,  only  silk  and  wool  are  of  much  technical  im- 
portance. Silk  fibre  forms  the  cocoon  of  the  silkworm,  Bombyx  mori. 
The  worm  has  two  glands,  situated  on  either  side  of  its  body,  each 
connected  by  a  duct  with  a  capillary  opening  (spinneret)  in  the  worm's 
head.  These  glands  each  appear  to  secrete  two  transparent  liquids ; 
the  one,  fibroine,  C15H23N506,  constituting  from  one-half  to  two-thirds 
of  the  whole  secretion,  forms  the  interior  and  larger  part  of  the  silk 
fibre;  the  other,  sericine,  C^H^lS^Os,  also  called  silk  glue,  is  yellowish 
in  color  and  is  readily  dissolved  in  boiling  water,  hot  soap  solutions, 
or  by  alkalies.  It  forms  the  outer  coating  of  the  fibre.  As  soon  as 
discharged  into  the  air,  the  fluids  from  the  spinnerets  solidify,  and 
coming  in  contact  with  each  other  at  the  moment  of  discharge,  are 
firmly  cemented  together  by  the  sericine ;  hence,  under  the  microscope 
the  fibre  shows  two  separate  structureless  filaments.  The  cocoon  is 
made  up  of  one  continuous  fibre,  from  350  to  1200  meters  long,  with 
an  average  diameter  of  .018  mm. 

Silkworms  are  raised  from  eggs  kept  in  an  incubator  from  twelve 
to  eighteen  days,  while  the  temperature  is  very  slowly  raised  from 
18°  to  25°  C.  The  caterpillars  have  a  prodigious  appetite,  and  are 
fed  regularly  on  mulberry  leaves  (Morus  alba,  L.,)  for  about  thirty 
days,  during  which  time  they  grow  rapidly,  casting  their  skins  every 
five  or  six  days,  and  attaining  a  length  of  about  8  cm.  Then  they 
cease  to  eat,  and  crawl  upon  twigs,  where  they  spin  their  cocoons. 
This  spinning  requires  about  three  days,  when  the  worms  are  killed 
by  heating  the  cocoons  in  an  oven  at  60°  to  70°  C.  for  three  hours,  or 
by  steaming  them  for  10  or  15  minutes.  After  sorting,  the  cocoons 
are  reeled.  This  is  an  entirely  mechanical  process  requiring  much 
skill.  The  cocoons  are  soaked  in  water  at  60°  C.,  until  the  silk  glue 
is  softened.  Then  the  operator  catches  the  loose  ends  of  several 
fibres  on  a  small  brush,  and  passes  them  through  the  agate  or  porce- 
lain guides  of  the  reel,  where  they  are  twisted  to  form  threads  of 
sufficient  size  for  weaving.  Two  threads  are  formed  simultaneously 
on  each  reel,  and  are  made  to  cross  and  rub  against  each  other  to 
remove  kinks  and  to  straighten  them,  and  also  to  rub  the  softened- 
silk-glue  coverings  together,  so  that  the  fibres  adhere  and  form 
solid,  uniform  threads,  — raw  silk.  There  is  considerable  waste,  con- 
sisting of  short  and  tangled  fibre  from  the  exterior  of  the  cocoons, 
and  from  those  which  have  been  opened  by  the  moth  in  escaping. 
This  is  worked  up  as  floss,  and  for  making  spun  silk. 

Raw  silk  is  exceedingly  hygroscopic,  and,  under  favorable  cir- 


TEXTILE   INDUSTRIES  439 

cum  stances,  will  absorb  as  much  as  30  per  cent  of  its  weight  of 
moisture,  and  still  seem  quite  dry.  It  is,  therefore,  customary  to 
determine  the  moisture  in  each  lot  at  the  time  of  sale.  This  is 
called  "conditioning,"  and  must  be  done  with  great  care,  usually  in 
official  laboratories.  A  sample  is  taken  from  each  bale,  and,  after 
careful  weighing,  is  dried  in  a  current  of  air  in  a  special  apparatus, 
at  a  temperature  of  110°  C.,  until  the  weight  becomes  constant. 
From  the  average  of  several  tests  the  absolute  amount  of  dry  silk  is 
determined,  to  which  the  legal  amount  of  moisture  permissible  (11 
per  cent)  is  added,  and  the  result  taken  as  the  weight  of  the  raw 
silk. 

Raw  silk  consists  of  about  25  per  cent  sericine,  the  remainder 
being  pure  fibroine,  and  has  a  very  harsh  feel  and  is  stiff  and  coarse. 
Before  it  is  made  into  yarn  or  cloth,  it  is  usually  subjected  to  vari- 
ous treatments  to  make  it  soft  and  glossy.  The  first  process  is 
called  discharging,  stripping,  or  ungumming,  and  its  purpose  is  to 
remove  more  or  less  of  the  silk  glue  (sericine)  from  the  fibre,  ac- 
cording to  the  kind  of  goods  desired.  The  hanks  of  silk  are  sus- 
pended on  wooden  sticks  in  a  vat  filled  with  soap  solution  at  95°  C. 
This  is  made  by  dissolving  Marseilles,  or  olein  soap  to  the  amount 
of  30  per  cent  of  the  weight  of  the  silk,  in  soft  water,  entirely  free 
from  lime.  The  hanks  are  turned  several  times  by  hand  in  this 
liquor,  during  a  period  of  from  one  to  one  and  a  half  hours ;  the 
fibres  swell,  become  sticky,  and  finally  the  sericine  dissolves,  leaving 
the  silk  glossy  and  soft.  The  soap  bath  is  not  boiled,  as  that  would 
tangle  the  fibres  and  cause  the  yellow  color  often  present  in  the 
sericine  to  become  fixed  on  them ;  also  long  boiling  weakens  silk. 
For  very  fine  work,  two  or  three  soap  baths  are  employed,  the  raw 
silk  being  first  put  into  that  which  has  been  longest  in  nse  and  which 
is  therefore  strongly  charged  with  dissolved  sericine ;  *  there  the 
glue  is  softened  and  partly  removed ;  the  hanks  are  transferred  to 
the  succeeding  baths  in  order,  finally  leaving  the  one.  most  recently 
prepared.  This  yields  very  soft,  white  silk,  which  is  rinsed  in  a 
warm  dilute  sodium  carbonate  solution  and  then  wrung.  That 
which  is  to  be  sold  as  white  silk  or  dyed  a  very  light  shade  is  then 
subjected  to  a  second  discharging  process,  in  which  the  hanks  are 
tied  in  several  places  with  tape,  enclosed  in  linen  bags,  and  boiled 
in  a  15  per  cent  soap  solution  from  one-half  to  three  hours,  to  remove 
all  the  glue.  This  product,  called  "  boiled-off  silk,"  has  lost  from  20 

*  The  soap  liquor  finally  becomes  heavily  charged  with  sericine  and  is  drawn 
from  the  tank  as  "  boiled-off  liquor."  It  is  used  in  making  up  the  dye  bath  for  silk 
dyeing,  pp.  481,  486,  and  489. 


440  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

to  30  per  cent  of  its  original  weight,  in  order  to  reduce  this  loss  of 
weight,  raw  silk  is  often  treated  in  a  weak  soap  bath  until  the  waxy 
matters  have  been  partly  removed,  and  is  then  washed  and  some- 
times bleached  by  exposure  to  sulphur  dioxide  vapors.  The  product, 
called  "  ecru  silk,"  is  harsh  to  the  touch,  but  has  lost  only  about 
from  2  to  4  per  cent  of  its  original  weight ;  it  is  chiefly  used  in  the 
warp  of  black  silk  and  for  the  back  of  velvet. 

Another  process  *  of  treating  raw  silk  for  dyeing,  while  leaving 
a  large  part  of  the  sericine  on  the  fibre,  is  employed  for  producing 
souple  silk.  The  hanks  are  first  scoured  in  a  10  per  cent  soap  solu- 
tion for  an  hour  or  two  at  25°  to  35°  C.  to  soften  and  swell  the  fibres. 
They  are  then  bleached  by  working  for  10  or  15  minutes  in  very  di- 
lute aqua  regia  or  in  a  dilute  solution  of  nitrous  acid  in  concentrated 
sulphuric  acid.  The  bleached  silk  is  then  exposed  to  sulphur  fumes 
for  several  hours,  until  sufficiently  white.  It  is  then  soupled,  i.e. 
worked  for  an  hour  and  a  half  in  a  solution  of  cream  of  tartar  or 
magnesium  sulphate,  3  or  4  grams  to  the  liter.  This  swells  and 
softens  the  fibre,  which  was  left  harsh  by  the  bleaching  process. 
Soupled  silk  has  lost  only  6  or  8  per  cent  of  its  original  weight,  but 
is  weaker  than  boiled-off  silk. 

Concentrated  mineral  acids,  especially  hydrochloric,  dissolve  silk 
completely.  Very  dilute  acids  are  absorbed  by  it,  thus  increasing 
the  lustre  and  imparting  a  peculiar  feel  to  the  fibre,  which  when 
compressed  emits  a  curious  rasping  sound  called  "scroop."  The 
property  of  scroop  may  be  given  by  treating  the  silk  in  a  bath  of  di- 
lute sulphuric,  acetic,  or  better,  tartaric  acid,  and  drying  without 
washing.  Caustic  alkalies  in  strong  solution  rapidly  destroy  silk  if 
heated ;  but  in  cold  solution,  caustic  soda  of  50°  Tw.  has  very  little 
action  on  the  fibre  and  may  be  used  to  produce  the  crinkled  appear- 
ance on  mixed  cotton  and  silk  goods  similar  to  seersuckers.  Ammo- 
nia has  little  or  no  action  on  the  fibroine  but  dissolves  the  sericine. 
Alkaline  carbonates  are  less  destructive  than  caustic,  but  attack  the 
fibre  slowly.  Borax  dissolves  sericine  without  material  injury  to  the 
fibroine,  but  is  not  so  good  as  soap  for  ungumming  raw  silk.  Lime 
water  swells  the  fibre,  makes  it  brittle,  and  dulls  the  lustre.  Chlo- 
rine destroys  silk  as  do  other  oxidizing  agents  unless  used  very  dilute 
and  with  much  care.  When  soaked  in  solutions  containing  metallic 
salts,  especially  iron,  aluminum,  tin,  lead,  or  copper,  silk  absorbs 
some  of  the  salt  and  a  precipitation  of  basic  salt  within  and  upon  the 
fibre  occurs.  On  this  fact  depends  the  weighting  of  silks  (p.  461). 

Besides  the  cultivated  silks,  certain  kinds  of  wild  silks  are  of 
*  Chemische  Technologie,  Wagner. 


TEXTILE  INDUSTRIES  441 

some  commercial  importance.  The  most  important  is  tussur  silk, 
obtained  from  the  cocoons  of  Indian  and  Chinese  moths,  Antliercea 
mylitta  and  A.  pernyi.  The  fibre  is  double  and  somewhat  flat,  each 
filament  being  composed  of  a  number  of  fibrillse.  It  is  brown  in 
color,  is  stift'er  and  coarser  than  ordinary  silk,  and  differs  in  its  chemi- 
cal composition,  containing  less  carbon  and  nitrogen  and  more  oxy- 
gen. It  is  more  resistant  to  the  action  of  alkalies  and  acids  and  to 
bleaching  agents.  It  is  difficult  to  bleach  and  dye,  and  is  chiefly  em- 
ployed in  making  pile  fabrics,  such  as  velvets,  plush,  and  imitation 
sealskin.  Other  wild  silks  are  nmga  silk  from  Anther cea  Assama, 
and  eria  silk  from  Attacus  ricini,  both  found  in  India :  yamamai  silk, 
from  Anthercea  yamamai  of  Japan ;  sea-silk  or  byssus,  produced  by 
a  mollusk,  Pinna  nobilis,  found  in  the  Mediterranean  Sea.  The 
fibre  of  sea-silk  is  brown  and  very  soft,  and  is  not  easily  affected  by 
acids  or  alkalies. 

The  following  analyses  from  HummePs  Dyeing  of  Textile  Fab- 
rics, are  of  interest. 

Composition  of  the  cocoons  :  — 

Moisture 68.2 

Silk 14.3 

Floss 0.7 

Chrysalis       16.8 

Composition  of  raw  silk :  — 

YELLOW  ITALIAN  SILK.         WHITE  LEVANT  SILK. 

Fibroine 53.37 54.04 

Gelatine 20.66 19.08 

Albumin 24.43 25.47 

Wax 1.39  .....  1.11 

Coloring  matter       ....        0.05 0.00 

Resinous  and  fatty  matter   .        0.10 0.30 

100.00  100.00 

The  ultimate  analysis  of  silk  fibroine  is  shown  in  the  following 
table:*  — 

Tcsstra  FIBROINB.  MULBERRY  FIBROINE. 

(Calculated  for  Cu^n^M 

Carbon   ....      47.18 47.78 

Hydrogen    .    .    .        6.30 6.23 

Nitrogen     .     .     .      16.85 18.90 

Oxygen  ....      29.67 26.04 

100.00  98.95 

*  Manual  of  Dyeing,  Knecht,  Rawson,  and  Loewenthal,  p,  56. 


442  OUTLINES  OF  INDUSTRIAL   CHEMISTRY 

Artificial  silk  is  made  from  certain  soluble  cellulose  nitrates  by 
Lehner's  process.  Ordinary  collodion,  containing  from  10  to  12  per 
cent  pyroxyline  in  solution,  is  treated  with  dilute  sulphuric  acid, 
which  causes  a  molecular  change,  making  the  substance  more  fluid. 
The  solution  is  filtered  and  made  to  flow  through  very  fine  glass  tubes, 
into  water,  which  at  once  coagulates  the  collodion.  The  transparent 
filament  formed  closely  resembles  the  natural  silk  fibre  in  appear- 
ance, and  several  of  them  are  twisted  together  into  a  thread  of  the 
desired  size,  which  is  wound  on  a  reel.  By  dehydrating,  the  thread 
becomes  white  and  highly  lustrous,  like  "boiled-off"  silk.  It  is 
still  very  inflammable,  and  is  next  "  denitrated  "  by  treating  it  with 
a  cold  solution  of  ammonium  sulphide,  which  destroys  the  cellulose 
nitrate  and  leaves  the  pure  cellulose  with  a  high  silky  lustre,  but  110 
more  inflammable  than  ordinary  cotton. 

Wool  is  the  hair  of  the  sheep,  but  that  of  certain  goats,  such  as 
the  alpaca,  cashmere,  and  mohair,  as  well  as  that  of  the  camel,  are 
also  classed  with  wools.  Wool  differs  from  true  hair  only  in  its 
physical  structure,  being  covered  with  minute  overlapping  scales  and 
having  a  twisted  or  curled  fibre.  The  character  of  wool  varies  with 
the  breed,  food,  and  care  of  the  sheep,  and  the  climate  and  nature  of 
the  soil  on  which  the  food  is  grown.  The  fibre  varies  from  short, 
fine,  and  wavy,  to  long,  coarse,  and  straight  in  different  breeds.  The 
length  ranges  from  1  inch  to  10  inches  in  different  varieties,  even 
reaching  16  inches  in  the  case  of  certain  cashmeres  and  mohairs. 
The  wool  cut  from  one  animal  is  called  a  fleece,  and  the  different 
grades  in  each  fleece  are  separated  by  hand,  that  from  the  neck,  back, 
and  shoulders  being  the  longest  and  best  quality.  The  long  staple 
wools  have  a  silky  appearance  and  are  often  called  lustre  wools. 
They  are  generally  used  for  worsted  goods,  while  the  short,  fine  wools 
are  made  into  woollen  goods.  Mohair,  obtained  from  the  Angora 
goat,  has  a  very  high  lustre  and  is  soft  and  fine,  as  are  also  the  al- 
paca, vicuna,  and  llama  wools  derived  from  South  American  goats. 

Sheep  pelts  are  often  soaked  in  "  milk  of  lime,"  or  sodium  sul- 
phide to  loosen  the  wool  before  making  leather  from  the  skin.  Such 
wool  is  known  as  "pulled  wool,"  and  is  of  poor  quality. 

Wool  is  very  hygroscopic,  and  may  contain  from  8  to  12  per  cent 
of  moisture  in  hot,  dry  weather,  up  to  50  per  cent  in  very  damp  air. 
On  an  average,  it  contains  about  18.25  per  cent,  and  this  is  the  legal 
limit  in  most  European  countries,  and  is  generally  determined  in 
"  conditioning  laboratories,"  as  in  the  case  of  silk.  The  temperature 
of  drying  is  kept  between  105°  and  110°  C.,  since  above  this  temper- 


TEXTILE   INDUSTRIES  443 

ature  there  is  danger  of  injuring  the  fibre.  At  100°  C.  wool  becomes 
plastic,  and  after  cooling  retains  the  shape  into  which  it  may  have 
been  formed  while  hot. 

Each  wool  fibre  is  covered  with  a  layer  of  broad  scales,  projecting 
in  the  same  direction  and  overlapping  much  like  shingles  on  a  roof, 
the  outer  edges  being  more  or  less  free.  When  the  approximately 
parallel  fibres  are  moved  upon  each  other  by  rubbing  or  "  milling," 
the  scales  interlock  and  cause  "felting."  The  interior  substance  of 
the  fibre  is  composed  of  narrow  cells  tapering  towards  each  end. 
Some  wools  also  have  a  central  or  medullary  part,  made  up  of  cells 
of  different  shape,  and  which  usually  contain  the  coloring  matter  of 
the  fibre.  Such  wools  are  stiff  and  brittle,  and  resemble  hair  in  their 
properties ;  the  best  wools  are  free  from  such  medullary  cells. 

The  internal  cells  appear  to  have  more  attraction  for  dyes  than 
do  the  outer  horny  scales,  and  much  of  the  effect  of  acids  and  other 
additions  to  the  dye-bath  is  supposed  to  be  due  to  the  raising  of 
these  scales  by  their  action,  thus  permitting  the  access  of  the  dye  to 
the  interior  substance.  Diseased  and  dead  fibres,  known  as  "kemp," 
do  not  color  well,  since  they  have  a  very  impenetrable  layer  of  these 
scales ;  moreover,  they  do  not  felt  properly,  and  are  dull  in  lustre. 

Pure  wool  fibre,  consisting  for  the  most  part  of  keratine,  the 
characteristic  constituent  of  horn,  feathers,  etc.,  is  not  of  constant 
chemical  composition,  varying  in  different  qualities  and  kinds.  The 
approximate  composition  of  keratine  from  wool  is :  — 

Carbon .  49.25* 

Nitrogen 15.86 

Hydrogen 7.57 

Sulphur 3.66 

Oxygen 23.66 

The  presence  of  sulphur  is  characteristic  of  wool,  and  often 
causes  difficulties  in  mordanting  and  dyeing.  The  ash  of  the  fibre 
averages  less  than  1  per  cent  of  the  weight  of  the  wool.  When 
heated  to  130°  C.,  with  water  under  pressure,  and  dried,  wool  is 
rendered  very  brittle.  Dilute  acids  have  no  apparent  action  on  it, 
but  a  small  percentage  is  absorbed  and  cannot  be  readily  removed 
by  washing ;  very  concentrated  mineral  acids  destroy  the  fibre.  By 
treating  mixed  cotton  and  wool  goods  with  a  dilute  sulphuric  or 
hydrochloric  acid,  and  drying  at  110°  C.,  the  cotton  is  "  carbonized  " 
(p.  435),  and  when  heated  crumbles  to  dust  and  falls  away  from  the 
unchanged  wool.  The  same  result  is  obtained  by  treating  the  goods 

*  Hummel,  Dyeing  of  Textile  Fabrics. 


444  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

with  hot,  dry  hydrochloric  acid  gas.  Alkalies  attack  wool  energeti- 
cally, the  caustic  alkalies  and  lime  being  most  destructive,  especially 
in  boiling  solution,  by  which  the  fibre  is  completely  destroyed. 
Alkaline  carbonates  are  much  less  injurious,  and  are  used  in  dilute 
solution  for  scouring  wool.  Ammonia  and  ammonium  carbonate 
have  very  little  tendering  effect  on  it,  and  are  best  for  washing, 
for  which  soap,  borax,  and  sodium  phosphate  are  also  used.  When 
strong  and  allowed  to  act  for  some  time,  oxidizing  agents  cause  the 
fibre  to  become  tender.  Very  dilute  solution  of  potassium  bichro- 
mate is  largely  used  in  mordanting  wool,  but  care  is  necessary  to 
prevent  "over  chroming."  When  moist,  chlorine  is  taken  up  by 
wool,  and  the  fibre  made  very  tender,  but  a  very  slight  treatment 
with  it  makes  the  wool  more  susceptible  to  certain  dyes ;  dry  chlo- 
rine is  said  to  have  no  action.  Wool  is  colored  yellow  by  hypo- 
chlorous  acid,  hence  bleaching  powder  is  not  used  to  bleach  the 
fibre.  When  boiled  in  solutions  of  various  metallic  salts,  it  absorbs 
a  considerable  amount  of  them,  and  it  is  often  so  treated  when  mor- 
danting before  dyeing.  The  nature  of  the  reactions  occurring  is  not 
clear,  but  apparently  there  is  a  direct  union  between  the  fibre  or 
some  of  its  constituents  and  the  salt.  Wool  has  great  affinity  for 
many  dyes,  and  the  colors  produced  are  generally  faster  than  when 
dyed  on  cotton  or  silk. 

Before  it  can  be  subjected  to  any  manufacturing  process,  raw 
wool  must  be  washed  and  scoured  to  remove  impurities,  which  are 
present  to  the  extent  of  from  30  to  80  per  cent  of  the  total  weight, 
These  consist  of:  (a)  yolk  or  wool  grease,  and  (6)  suint,  which 
exude  from  the  body  of  the  animal  with  the  perspiration ;  and  (c) 
dirt  mechanically  mixed  with  them  or  entangled  among  the  fibres. 

The  wool  grease  is  soluble  in  ether,  benzene,  or  carbon  disulphide, 
and  is  made  up  of  fatty  or  wax-like  bodies,  consisting  largely  of 
solid  alcohols,  especially  cholesterine  and  isocholesterine,  together 
with  the  oleic,  palmitic,  and  stearic  acid  esters  of  those  alcohols. 
These  substances  are  not  easily  saponified  with  alkali,  but  can  be 
emulsified  with  soap  solution,  and  thus  easily  removed  from  the 
fibre. 

Suint  is  soluble  in  water,  and  consists  mainly  of  potassium  salts 
of  oleic,  stearic,  valeric,  and  acetic  acids,  together  with  sulphates, 
chlorides,  and  phosphates,  and  nitrogenous  bodies. 

These  are  generally  removed  by  washing  in  a  solution  of  soap. 
A  soft  soap,  made  from  Gallipoli  oil  (p.  313),  is  preferred  for  the 
best  qualities  of  wool,  but  usually  a  cheaper  soap,  containing  some 
sodium  carbonate,  is  employed.  The  washing  is  done  in  machines, 


TEXTILE   INDUSTRIES  445 

and  care  is  taken  not  to  entangle  the  fibre  any  more  than  need  be. 
There  are  usually  three  tanks,  placed  en  cascade,  and  so  arranged 
that  the  wool  may  be  automatically  passed -from  one  to  the  next, 
while  the  liquor  is  drawn  from  one  to  the  other  in  a  direction  oppo- 
site to  the  movement  of  the  wool.  The  raw  wool  is  introduced  into 
the  soap  liquor  containing  more  or  less  impurity  from  its  previous 
use  in  the  other  tanks.  The  temperature  should  be  from  35°  to 
40°  C.,  but  is  generally  higher.  The  wool  is  submerged  and  pushed 
forward  a  short  distance  by  prongs  or  gratings  which  work  auto- 
matically. At  each  stroke,  a  portion  of  the  wool  is  caught  and 
pushed  between  squeeze-rolls,  which  expel  the  liquor ;  it  then  passes 
into  the  next  tank,  where  it  is  washed  in  the  same  way  with  cleaner 
soap  liquor,  and  then  goes  through  squeeze-rolls  into  the  last  tank, 
containing  clear  water  or  fresh  soap  liquor.  The  wash  liquor,  aided 
by  the  free  alkali  added  and  the  potassium  oleate,  etc.,  in  the  suint, 
emulsifies  and  dissolves  the  wool  grease  and  suint,.  loosening  the 
mechanical  impurities,  which  sink  to  the  bottom.  After  wash- 
ing in  clean  water,  the  wool  is  dried  on  wire  netting  by  a  current 
of  warm  air.  The  foul-smelling,  dirty  brown  liquor  from  the  first 
tank  is  drawn  off,  and  may  be  evaporated  directly  and  calcined  to 
recover  the  potash,  which  amounts  to  from  1  to  8  per  cent  of  the 
weight  of  the  wool.  Or  it  may  be  treated  to  recover  the  wool 
grease,  sometimes  called  Yorkshire  grease;  it  is  settled  to  remove 
coarse  dirt,  and  then  sulphuric  acid  is  added  in  slight  excess,  to 
decompose  the  soaps  and  set  free  the  fatty  acids,  which  rise  to  the 
surface,  carrying  the  wool  grease  with  them.  The  water  is  drawn 
off  from  the  magma,  which  is  pressed,  hot,  in  canvas  bags.  The 
grease  is  kept  in  a  liquid  condition  until  all  sediment  deposits,  when 
it  is  drawn  into  casks,  where  it  solidifies  on  cooling.  It  is  used  as  a 
lubricator,  and  in  leather  dressing. 

By  passing  the  clarified  wash  liquor  through  a  machine  similar 
to  a  cream  separator,  the  grease  is  very  neatly  separated  from  it. 
For  the  preparation  of  lanolin  from  this  grease,  see  p.  320. 

Wool  is  often  treated  by  methods  intended  to  recover  the  yolk 
and  suint  separately.  This  is  usually  done  by  extracting  first  with  a 
volatile  solvent  (carbon  disulphide  or  petroleum  spirit)  to  remove  the 
wool  grease,  and  then  washing  the  wool  in  water  to  remove  the  suint. 

The  washed  wool  is  harsh  and  brittle,  and  before  being  manu- 
factured must  be  softened  by  oiling.  Pure  olive  oil  is  best  for  this, 
but  lard,  colza,  hemp  and  mineral  oils,  and  sometimes  "red  oil" 
(oleic  acid)  are  also  used.  This  in  turn  must  be  removed  by  scour- 
ing before  dyeing. 


446  OUTLINES  OF  INDUSTRIAL   CHEMISTRY 

Wool  was  formerly  scoured  by  treatment  with  stale  urine,  called 
"lant,"  its  efficiency  being  due  to  the  ammonium  carbonate  in  it.  But 
this  method  has  been  generally  abandoned  in  favor  of  soap-scouring. 
The  addition  of  a  little  ammonium  carbonate  to  the  soap  bath  would 
improve  its  action,  but  the  salt  is  too  expensive  for  general  use. 


BLEACHING 

Natural  fibres,  whether  vegetable  or  animal,  always  contain  cer- 
tain coloring  matters,  which,  even  though  present  in  very  small  quan- 
tities, impair  the  purity  of  the  white,  desirable  in  most  uncolored 
fabrics.  Moreover,  there  are  always  certain  gums,  waxes,  resins, 
and  oily  matters  on  the  fibre,  either  natural  to  it,  or  added  to  facili- 
tate the  spinning  and  weaving  operations.  In  woven  goods  there 
is  more  or  less  sizing  material,  consisting  of  starch,  china  clay, 
metallic  salts,  and  oxides,  etc.,  put  upon  the  fibre  to  assist  in  the 
weaving  or  to  improve  the  appearance  or  weight  of  the  cloth.  If 
left  upon  the  goods,  these  substances  will  prevent  the  proper  action 
of  mordants  and  dyes,  while  some  of  them  detract  from  the  appear- 
ance of  those  fabrics  which  are  to  be  sold  uncolored.  It  is  the  work 
of  the  bleacher  to  remove  all  these  foreign  substances  and  decolorize 
the  fibre. 

In  general,  the  bleaching  process  is  divided  into  two  stages, 
the  washing  or  scouring,  and  the  bleaching  proper  or  chemical 
treatment.  The  method  of  treatment  and  the  material  used  vary 
with  the  different  kinds  of  fibre. 

COTTON   BLEACHING 

Cotton  is  commonly  bleached  in  the  yarn  or  woven  piece,  since 
there  is  no  special  demand  for  bleached  cotton-wool. 

Yarn  bleaching.  —  If  the  cotton  is  to  be  dyed  in  dark  colors,  it  is 
customary  to  give  it  a  thorough  boiling  in  water  alone,  or  with  the 
addition  of  some  soda-ash,  to  remove  the  grease,  wax,  and  resinous 
matters.  After  washing,  it  is  at  once  dyed.  But  for  white  yarn, 
or  that  to  be  dyed  any  light  shade,  the  bleaching  process  is  more 
complicated.  The  hanks  of  yarn  are  linked  together  to  form  a 
chain,  and  then  loosely  packed  into  a  closed  iron  vessel,  called 
a  "  kier,"  where  they  are  boiled  for  several  hours  with  caustic  soda  or 
soda-ash,  under  a  low  pressure  (5  pounds  per  square  inch),  or  even 
in  open  vessels.  The  kier  has  a  false  bottom,  upon  which  the  yarn 
rests.  A  vertical  pipe  passes  up  through  the  centre  of  the  kier,  to 


TEXTILE  INDUSTRIES  447 

within  a  few  inches  of  the  top.  Across  the  upper  end  of  this  pipe 
is  a  dome-shaped  bonnet,  and  at  the  lower  end  is  a  steam  injector 
which  forces  the  liquor  collected  under  the  false  bottom  up  through 
the  pipe  against  the  bonnet,  which  distributes  it  over  the  yarn, 
through  which  it  percolates,  collecting  under  the  false  bottom. 
Thus  a  constant  circulation  of  the  liquor  is  maintained  in  the  kier. 
On  an  average  about  4  per  cent  (of  the  weight  of  the  goods)  of  soda- 
ash  is  used  in  the  lye. 

The  yarn  is  then  washed  with  clean  water  and  is  treated  with  a 
cold  dilute  bleaching  powder  solution,  called  the  "  chemick."  This 
is  about  2°  Tw.,  and  is  pumped  over  the  yarn  as  it  lies  in  a  wooden 
tank  having  a  false  bottom.  After  5  or  6  hours  the  yarn  is  re- 
moved, squeezed,  and  washed  in  water  for  a  few  minutes.  It  is  then 
"  soured "  by  plunging  into  a  tank  containing  a  dilute  sulphuric  or 
hydrochloric  acid  of  about  1°  Tw.  Chlorine  is  thus  liberated  from  the 
bleach  absorbed  in  the  fibre,  and  sets  free  oxygen  from  the  water, 
which  at  once  attacks  and  destroys  the  coloring  matters,  the  yarn 
becoming  pure  white.  This  process  requires  about  15  to  20  minutes ; 
then  the  yarn  is  thoroughly  washed  in  water  and  passed  into  a  hot 
soap  solution,  to  which  a  little  bluing  (ultramarine)  has  been  added, 
if  the  yarn  is  to  be  sold  uncolored.  The  soap  is  worked  into  the 
yarn  by  squeeze-rolls,  until  the  fibres  are  uniformly  blued ;  then  the 
excess  of  soapy  water  is  removed  in  a  centrifugal  machine,  and 
the  yarn  is  dried. 

One  of  the  best  machines  for  yarn  washing  is  the  Haubold  ma- 
chine. This  consists  of  a  circular  tub  containing  a  rotating  central 
shaft  from  which  square  bobbins  radiate.  OH  these  the  hanks  are 
hung,  and  as  they  are  carried  slowly  forward,  a  suitable  gearing 
imparts  to  the  bobbins  an  intermittent  forward  and  backward  rota- 
tion on  their  own  axes.  The  tank  is  divided  by  a  radial  partition, 
on  one  side  of  which  fresh  water  enters,  while  on  the  other  the  dirty 
water  flows  out.  The  hanks  are  moved  against  the  current  of  water, 
and  are  taken  out  when  they  come  to  the  partition  on  the  side  where 
the  clean  water  enters. 

In  other  washing  machines,  the  yarn  is  pounded  by  heavy 
wooden  hammers  driven  by  power.  Or,  as  shown  in  Fig.  92,  the 
hanks  tied  together  to  form  a  chain  are  washed  by  passing  through 
squeeze-rolls  (A,  A)  and  under  a  stretching  roller  (B),  placed  in  the 
bottom  of  the  wash  tank.  The  yarn  thus  passes  down  and  up  under 
the  rollers  and  between  the  squeeze-rolls  several  times. 

Improved  apparatus  is  now  employed,  in  which  the  lye-boiling, 
chemicking,  souring,  and  washing  are  all  carried  on  in  one  wooden 


448 


OUTLINES  OF  INDUSTRIAL   CHEMISTRY 


vessel.  The  yarn  is  not  moved  during  the  process,  and  the  various 
liquors  are  pumped  through  the  apparatus  in  their  order,  and  the 
labor  is  thus  much  reduced. 

The  most  important  branch  of  cotton  bleaching  is  the  bleaching 
of  cloth.  It  is  done  by  one  of  three  methods :  the  market  bleach  for 
goods  to  be  sold  as  white  muslin;  the  Turkey-red  bleach,  for  goods 
to  be  dyed  red  with  alizarin ;  the  madder  bleach  designed  for  cloth 
which  is  to  be  printed  with  various  mordants  and  then  dyed  in  a 
bath  of  madder  or  alizarin.  It  is  the  most  thorough,  and  leaves 
the  cotton  white  and  almost  pure  cellulose.  It  is  necessary  to  re- 
move every  impurity  which  can  attract  the  dye  or  prevent  its  taking 


FIG.  92. 

the  fibre.  If  the  cotton  is  not  chemically  clean  before  printing,  the 
pattern  will  not  be  clear  and  sharp,  nor  the  background  a  pure 
white. 

The  madder  bleach  is  carried  out  as  follows :  The  separate 
pieces  of  goods  are  marked  on  the  ends  for  future  identification, 
and  then  stitched  together,  end  to  end,  to  form  a  continuous  web, 
which  is  first  "singed"  to  remove  the  lint,  floss,  and  loose  hairs, 
as  these  would  prevent  the  printing  of  sharp  designs.  This  may  be 
done  by  passing  the  cloth,  opened  to  its  full  width,  over  one  or  two 
red-hot  copper  plates,  slightly  curved  and  set  in  the  roof  of  a  fur- 
nace ;  it  is  difficult  to  keep  these  evenly  heated,  owing  to  the  cooling 
effect  of  the  rapidly  moving  cloth,  and  the  singeing  is  liable  to  be 
imperfect  in  places.  Consequently  a  revolving  hollow  roll  is  some- 
times used,  which  is  kept  red  hot  by  passing  the  flames  of  the  fur- 
nace through  it  on  their  way  to  the  chimney.  Or  the  cloth  may  be 
passed  over  a  row  of  Bunsen  gas  flames.  Directly  over  these  is  a 


TEXTILE  INDUSTRIES 


449 


small  roller,  under  which  the  cloth  passes  at  sufficient  tension  to 
cause  the  "nap"  to  stand  out  well  as  it  comes  into  the  flame.  As 
soon  as  the  cloth  passes  the  hot  plate  or  flame  it  is  plunged  into  a 
trough  of  water,  to  extinguish  any  sparks. 

The  goods  are  then  thoroughly  wet  in  water  (the  "gray-wash"), 
and  much  of  the  sizing  and  dirt  is  removed.  The  cloth  is  then 
usually  piled  in  a  heap  and  left  over  night,  to  thoroughly  soften 
the  gums  and  starchy  matters  left  in  it.  It  is  then  given  the  "  lime- 
boil,"  with  milk  of  lime  under  pressure  preferably  in  the  injector 
kier.  The  cloth  is  passed  through  a  trough  of  milk  of  lime,  of 
which  it  absorbs  about  4  or  5  per  cent  of  its  own  weight.  Without 
wringing,  it  is  passed  into  the  kier, 
which  is  filled  nearly  full,  and  packed 
by  boys,  who  tread  the  cloth  down 
evenly,  so  that  the  liquor  will  be 
forced  to  pass  through  it,  and  not 
through  channels  between  the  folds. 
Water  is  introduced,  and  then  steam 
is  blown  in  until  the  air  is  expelled 
and  the  kier  is  hot,  when  the  cover  is 
screwed  down  and  the  boiling  con- 
tinued under  from  10  to  70  pounds 
pressure,  for  several  hours.  The  kier 
(Fig.  93  *)  is  made  of  boiler  plate,  and 
is  from  6  to  10  feet  high  by  4  to  6 
feet  in  diameter;  it  will  hold  from 
600  to  3500  pounds  of  cloth.  Steam 
is  admitted  through  (A),  and  passing 

the  injector  (G),  draws  the  lime  water  through  (B)  and  delivers 
it  through  (C)  to  the  nozzle  (N),  which  sprays  it  over  the  goods. 
The  pressure  in  the  upper  part  of  the  kier  forces  the  liquor  through 
the  goods,  and  it  collects  among  quartz  pebbles  in  the  bottom,  whence 
it  is  drawn  through  (B)  to  the  top  of  the  kier.  If  needed,  water  is 
admitted  through  (D)  and  milk  of  lime  through  (E).  At  the  end  of 
the  operation  the  waste  liquor  is  drawn  off  through  (F). 

The  object  of  this  lime-boil,  or  "lime-bowk,"  as  it  is  sometimes 
called,  is  to  convert  the  fatty  matters  into  lime  soap,  to  dissolve  the 
remaining  starch  and  other  soluble  substances,  and  to  so  change  the 
natural  impurities  chemically,  that  they,  together  with  the  lime  soap 
formed,  are  readily  removed  in  succeeding  operations. 

The  cloth  is  usually  darker  after  this  treatment  than  before.     It 
*  After,  Knecht,  Rawson  and  Loewenthal,  Manual  of  Dyeing. 

2G 


450  OUTLINES  OF   INDUSTRIAL   CHEMISTRY 

is  next  washed  in  machines  similar  to  that  shown  in  Fig.  92,  to  re- 
move excess  lime,  soluble  matters,  and  loose  dirt.  The  rope  of  cloth 
is  thus  passed  through  the  water  and  between  the  rolls  (A,  A)  several 
times,  while  it  is  sprayed  by  a  heavy  stream  of  water  from  the  pipe 
(C)  as  it  comes  up  to  the  squeeze-rolls. 

It  now  passes  to  the  first-sour,  or  gray-sour,  where  it  is  treated 
with  dilute  sulphuric  or  hydrochloric  acid  at  1°  or  2°Tw.;  this  de- 
composes the  lime  soap,  and  removes  any  iron  stains  and  other 
metallic  oxides.  The  goods  are  then  passed  through  squeeze-rolls, 
to  remove  the  excess  of  acid,  and  are  thoroughly  washed  to  prevent 
the  acid  from  rotting  the  fibre,  as  it  would  on  long  exposure  to  the 
air. 

The  lye-boils,  of  which  there  are  two  or  three,  are  also  carried  on 
in  the  injector  kier.  In  the  first  boiling  the  goods  are  treated  with 
1  per  cent  soda-ash*  for  about  3  hours;  in  the  second  about  3.6  per 
cent  soda-ash,  0.8  per  cent  caustic  soda,  and  1.6  per  cent  of  rosin  are 
used,  and  the  whole  boiled  for  12  hours ;  the  third  lye-boil  is  with 
soda-ash  alone,  and  continues  for  3  hours.  These  boilings  remove 
the  remaining  fats  and  oils  from  the  lime  soaps,  and  extract  much 
of  the  brown  coloring  matter.  The  addition  of  rosin  is  a  character- 
istic of  the  madder  bleach,  and  is  supposed  to  remove  certain  sub- 
stances from  the  cotton  which  readily  attract  the  dye. 

After  a  thorough  washing,  the  next  process  is  the  "  chemicking," 
or  treatment  with  bleaching  powder,  which  is  done  in  a  machine 
similar  to  the  squeeze-rolls  used  in  the  souring.  The  cloth  while 
still  wet  is  passed  through  a  clear,  cold  solution  of  bleaching  powder 
at  y  to  2°  Tw.  It  is  then  piled  in  a  heap  and  left  for  some  hours. 
The  bleach  is  partly  decomposed  by  the  carbon  dioxide  of  the  air, 
and  hypochlorous  acid  is  set  free ;  this  decomposes  in  the  presence 
of  organic  coloring  matter,  liberating  oxygen,  which  destroys  the 
color.  If  the  bleach  liquor  is  too  strong  the  cotton  is  attacked  and 
oxy cellulose  formed,  which  is  objectionable. 

After  the  chemick,  the  cloth  is  piled  for  a  few  hours ;  then  it  is 
next  subjected  to  the  "  white-sour."  It  is  treated  with  dilute  min- 
eral acid,  to  complete  the  liberation  of  chlorine  from  the  bleach 
remaining  in  the  fibre.  Hydrochloric  acid  is  the  best  for  this,  since 
it  renders  the  lime  more  soluble.  The  cotton  is  completely  decolor- 
ized, and  after  about  three  hours  is  thoroughly  washed.  It  is  passed 
through  squeeze-rolls,  and  then  opened  out  smooth  and  passed  over 
large  copper  drums,  heated  by  steam,  to  dry  it  thoroughly.  The 
whole  time  necessary  for  the  madder  bleach  is  about  five  days. 
*  These  percentages  are  calculated  on  the  weight  of  the  goods. 


TEXTILE   INDUSTRIES  451 

For  24,000  kilos  of  cloth  the  following  scheme  is  given  by  Hum- 
mel :  *  — 

1.  Wash  after  singeing. 

2.  Lime-boil:  1000  kilos  lime ;  boil  12  hours;  wash. 

3.  Lime-sour :  hydrochloric  acid,  2°  Tw. ;  wash. 

4.  Lye-boils :  — 

1st :  340  kilos  soda-ash  (li  per  cent  ash) :  boil  3  hours. 


2d:    860  kilos  soda-ash  (  =  3.6  per  cent). 
380  kilos  rosin  (=  1.6  per  cent). 
190  kilos  solid  caustic  soda  (=  0.8  percent). 


Boil 

12 

hours. 


3d:    380  kilos  soda-ash   (=1.6   per   cent);    boil   3   hours; 

wash. 

5.  Chemicking :  bleaching  powder  solution,  y  to  y  Tw. ;  wash. 

6.  White-sour :  hydrochloric  acid,  2°  Tw. ;  pile  1  to  3  hours. 

7.  Wash,  squeeze,  and  dry. 

The  Turkey-red  bleach  is  employed  for  cotton  which  is  to  be 
dyed  a  full  color  with  alizarin  red.  It  is  essential  that  the  fibre 
shall  not  be  singed  nor  exposed  to  chlorine,f  since  the  development 
of  a  brilliant  red  would  be  thus  prevented.  The  process  is  there- 
fore simpler,  the  outline  for  2000  kilos  of  cloth  being  as  follows  :  $  — 

1.  Wash. 

2.  Boil  2  hours  in  water ;  wash. 

3.  Lye-boils :  — 

1st:  90  liters  of  caustic  soda  solution,  70° Tw.  (=  4-j-  per 
cent  of  weight  of  goods)  ;  boil  10  hours ;  wash. 

2d:  70  liters  of  caustic  soda  solution,  70°  Tw.  (=  3J  per 
cent  of  weight  of  goods)  ;  boil  10  hours  ;  wash. 

4.  Sour :  sulphuric  acid,  2°  Tw. ;  steep  2  hours. 

5.  Wash  well,  and  dry. 

The  market  bleach  differs  from  the  madder  bleach  chiefly  in  that 
the  singeing  and  rosin-boil  are  omitted  and  the  cloth  is  starched  and 
blued  slightly  before  drying.  An  outline  of  the  process  is  about  as 
follows :  — 

1.  Gray-wash. 

2.  Lime-boil :  8  to  12  hours ;  wash. 

*  Dyeing  of  Textile  Fabrics,  p.  77. 

t  The  injurious  action  of  the  chlorine  is  supposed  to  be  due  to  the  formation  of 
oxycellulose.    J.  Soc.  Dyers  and  Colorists,  1886,  29. 
J  Hummel,  Dyeing  of  Textile  Fabrics,  p.  85. 


452  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

3.  Lime-sour:    hydrochloric  acid,  2°  Tw. ;    steep  2   to  4  hours; 

wasli  well. 

4.  Lye-boils :  — 

1st.    1^-  to  3  per  cent  soda-ash ;  boil  3  to  12  hours. 
2d.    1  ^  to  3  per  cent  soda-ash ;  boil  3  to  12  hours ;  wash 
well. 

5.  Chemick :  bleaching  powder  solution,  -J-0  to  -J-0  Tw. ;  pile  6  to 

12  hours. 

6.  White-sour :  hydrochloric  acid,  2°  Tw. ;  pile  3  hours ;  wash. 

7.  Starched  and  blued. 

8.  Calendered. 

9.  Tentered  and  folded. 

Much  care  is  taken  in  the  finishing  operations.  The  bluing  is 
generally  mixed  with  the  boiled  starch,  and  after  passing  through 
squeeze-rolls,  the  lightly  starched  cloth  goes  to  the  calender  ma- 
chine. Here  it  is  heavily  pressed  between  hot,  polished  steel  rolls 
to  give  it  a  smooth  and  glossy  surface.  Next  it  goes  to  the  tenter- 
ing  machine,  which  consists  of  a  travelling  frame  with  parallel 
sides,  carrying  clips  or  hooks,  to  which  the  cloth  is  fastened  by  the 
selvedges.  The  side  rods  of  the  frame  have  an  intermittent  back- 
ward and  forward  movement  which  stretches  and  draws  the  cloth 
in  the  direction  of  its  width.  Beneath  are  a  number  of  flat  steam- 
boxes,  the  heat  from  which  rapidly  dries  the  cloth.  Finally,  it  goes 
to  a  folding  machine,  by  which  the  cloth  is  laid  in  folds  one  yard  in 
lengbh ;  the  number  of  yards  required  for  a  bolt  is  then  cut  off. 

Various  modified  bleaching  processes  have  been  devised,  chiefly 
with  the  view  of  saving  time,  labor,  and  wear  on  the  goods.  That 
of  Horace  Koechlin  has  been  introduced  in  some  works.  The  lime- 
boil  is  abolished,  and  a  single  caustic  soda  and  rosin-boil  is  substi- 
tuted for  the  lye-boils.  A  special  horizontal  kier  is  used,  into  which 
cars  packed  with  the  cloth  can  be  run.  The  boiling  here  is  not 
essentially  different  from  that  in  the  ordinary  form,  but  the  cars 
are  run  out  and  others  immediately  run  in,  without  material  cooling 
of  the  kier ;  thus  much  time  is  saved.  The  chemicking,  souring, 
and  washing  are  carried  on  in  the  usual  way. 

In  the  Mather-Thompson  process*  the  same  kier  is  used  as  in 
the  Koechlin  process,  but  a  special  apparatus  is  employed  for  the 
subsequent  chemicking,  followed  by  a  soda-boil  and  a  second  chem- 
icking. After  passing  through  the  bleaching  powder  solution  the 

*  For  details  of  this  process,  see  Thorpe's  Dictionary  of  Applied  Chemistry, 
Vol.  I,  321. 


TEXTILE   INDUSTRIES 

cloth  is  exposed  to  the  action  of  carbon  dioxide  gas  to  set  free  the 
hypochlorous  acid ;  this  hastens  the  bleaching. 

The  Hermite  bleaching  process*  depends  upon  the  electrolytic 
decomposition  of  magnesium  or  aluminum  chloride,  to  form  bleach 
liquors  consisting  of  hypochlorites  of  these  metals ;  the  liquors  are 
employed  instead  of  bleaching  powder  for  chemicking. 

Peroxide  of  hydrogen  used  in  conjunction  with  soap,  magnesia, 
and  caustic  soda  in  a  boiling  bath  gives  an  excellent  bleach  on 
cotton.  But  its  cost  is  yet  too  great  to  allow  of  its  general  use  for 
this  purpose. 

Permanganate  of  potassium,  in  slightly  acid  solution,  gives  a 
very  good  bleach  on  cotton  which  has  been  boiled  in  caustic  soda 
to  remove  gums  and  oily  matters.  Alkaline  permanganate  must  be 
avoided,  as  it  forms  oxy cellulose.  When  removed  from  the  perman- 
ganate bath,  the  goods  are  colored  a  deep  brown,  but  a  pure  white 
is  produced  by  passing  them  into  a  bath  of  sodium  bisulphite  or 
sulphurous  acid.  The  process  is  worked  cold  and  the  goods  must 
be  thoroughly  washed  after  bleaching. 

LINEN   BLEACHING 

Linen  contains  more  than  25  per  cent  coloring  matter  and  other 
impurities  (chiefly  pectic  acid,  so-called),  and  the  bleaching  process 
is  more,  difficult  and  tedious,  although  essentially  similar  to  that 
used  for  cotton.  Linen  is  more  readily  attacked  by  alkalies,  acids, 
or  chlorine,  and  more  care  and  time  (from  3  to  6  weeks)  are  needed 
to  prevent  injury  to  the  fibre.  The  liquors  are  much  weaker  and 
the  processes  are  usually  repeated  several  times.  It  is  also  cus- 
tomary to  "  grass  "  linen  for  a  week ;  i.e.  to  expose  it  to  the  sun  and 
dew  by  spreading  it  on  the  grass.  It  is  frequently  moistened  to 
assist  in  the  bleaching.  It  is  supposed  that  the  ozone  in  the  air  is 
here  the  active  agent. 

Linen  is  bleached  in  the  form  of  thread,  yarn,  or  cloth.  Accord- 
ing to  the  degree  of  whiteness,  it  is  said  to  be  quarter,  half,  or  three- 
quarters  bleached,  but  the  strength  of  the  fibre  diminishes  as  the 
purity  of  the  white  increases.  The  following  outline  of  the  Irish 
process  for  yarn  bleaching  is  according  to  Hummel  | :  — 

1.  Lye-boil :  10  per  cent  soda-ash  in  solution,  boil  3  to  4  hours, 

wash  and  squeeze. 

2.  Chemick:  reel  one  hour  in  bleaching  powder  solution  at  i° 

Tw. ;  wash. 

*  Hurter,  J.  Soc.  Chem.  Ind.,  1887,  337. 
t  Hummel,  Dyeing  of  Textile  Fabrics,  p.  88. 


454  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

3.  Sour :  steep  one  hour  in  sulphuric  acid  at  1°  Tw. ;  wash. 

4.  Lye-boil  (scald.) :  boil  one  hour  with  2  to  5  per  cent  soda-ash 

in  solution ;  wash. 

5.  Chemick :  reel  again  as  in  (2)  ;  wash. 

6.  Sour,  as  in  (3)  ;  wash  well  and  dry. 

This  gives  a  half  bleach ;  for  three-quarters  bleach,  repeat  Nos. 
4,  5,  and  6,  but  after  the  lye-boil  (4),  grass  for  a  week;  and  in 
(5),  instead  of  reeling  the  yarn,  allow  it  to  steep  in  the  bleach 
liquor  for  10  to  12  hours. 

Linen  piece  goods  *  are  bleached  similarly  to  cotton  cloth,  but 
the  details  vary.  There  are  the  same  lime-boil,  sour,  and  several 
lye-boils  with  caustic  soda,  then  a  grassing  for  several  days,  followed 
by  a  chemick,  sour,  and  third  soda-boil,  another  grassing,  and  a 
second  chemick.  If  not  white,  the  goods  are  rubbed  between  rub- 
bing boards  with  a  strong  soap  solution,  to  remove  mechanically  the 
fine  black  specks  called  "sprits'7  adhering  to  the  fibre.  This  is 
followed  by  a  third  grassing,  chemick,  sour,  and  washing. 

Potassium  permanganate  has  been  recommended  for  linen  bleach- 
ing in  conjunction  with  sulphurous  acid  or  hydrogen  peroxide. 
These  substances  are  said  to  act  rapidly  and  to  reduce  the  time  of 
bleaching  to  a  few  days. 

Jute  is  bleached  by  simple  treatment  with  bleaching  powder 
solution,  followed  by  a  sour  and  a  thorough  washing.  The  bleach 
liquor  is  very  strong,  and  the  temperature  rather  high,  37°  to  48°  C. 
For  a  full  bleach,  three  baths  of  bleach  liquor  are  used,  varying  in 
strength  from  20  per  cent  down  to  5  per  cent  of  bleaching  powder, 
the  yarn  being  hung  in  each  tank  for  about  three-quarters  of  an 
hour.  Unless  this  is  carefully  done,  the  fibre  is  weakened.  The  use 
of  weak  hypochlorite  of  sodium  is  advocated  in  place  of  bleaching 
powder,  the  soda,  it  is  claimed,  preventing  the  formation  of  chlo- 
rinated derivatives  of  the  jute.  (In  the  presence  of  water,  chlorine 
combines  with  the  jute,  forming  yellow  chlorination  products.) 

Hemp  is  not  often  bleached,  since  its  chief  use  is  for  cordage  and 
twine,  where  the  color  is  of  no  consequence.  It  is  sometimes  par- 
tially bleached  by  boiling  in  sodium  silicate,  washing  and  treating 
with  bleaching  powder  solution  for  some  hours,  then  souring  in 
dilute  acid  and  washing  thoroughly. 

*  Herzfeld,  Handbuch  der  Farberei,  p.  376.    Also  see  Hummel. 


TEXTILE   INDUSTRIES  455 

'WOOL   BLEACHING 

The  preliminary  operations  of  washing  and  scouring  the  loose 
wool  have  already  been  described  on  p.  444.  After  spinning,  the 
yarn  is  left  greasy,  and  a  second  scouring  is  necessary  before  bleach- 
ing or  dyeing. 

Wool  yarn,  especially  when  tightly  twisted,  shows  a  decided  ten- 
dency to  curl  and  shrink  when  wet  in  warm  water.  As  this  would 
cause  tangles  and  felting  in  the  scouring  and  dyeing,  the  yarn  is 
stretched  on  a  strong  frame  carrying  a  number  of  projecting  arms. 
A  hank  of  yarn  is  hung  over  two  of  these  arms,  and  is  stretched 
tight  by  means  of  screws  which  separate  the  arms.  When  filled, 
the  frame  is  submerged  in  boiling  water  for  half  an  hour.  It  is  then 
taken  out,  and  the  yarn  allowed  to  cool  while  stretched.  The  hanks 
are  then  shifted  so  that  the  portion  that  was  in  contact  with  the 
arms  now  comes  between  them,  and  the  entire  process  repeated.  This 
removes  all  the  "  curl,"  and  the  yarn  is  ready  for  scouring,  which 
may  be  done  by  hand  or  in  machines.  In  the  first  method,  the 
hanks  are  suspended  from  wooden  rods  in  the  tank  containing  the 
hot  scouring  liquor  (soap  solution),  and  are  swung  to  and  fro,  with 
frequent  turning  of  the  rod,  to  wet  all  parts  of  the  hank.  They  are 
then  washed  by  swinging  them  in  a  tank  of  water.  An  effective 
scouring  machine  for  yarn  consists  of  a  pair  of  squeeze-rolls  placed 
over  a  tank  filled  with  soap  liquor,  and  containing  several  rollers, 
under  and  over  which  the  hanks,  tied  together  in  a  chain,  are  passed. 
Woollen  cloth  may  be  scoured  in  a  scouring  machine  called 
a  "  dolly " ;  the  cloth  is  passed  as  a  rope,  through  the  soap  liquor, 
and  then  between  squeeze-rolls.  But  "goods  which  are  liable  to 
crease  must  be  scoured  in  the  open-width  scouring  machine. 
The  cloth  is  then  sprayed  with  clean  water,  returned  to  the  soap 
bath,  and  again  put  through  the  squeeze-rolls.  The  dirty  soap 
liquor  expressed  is  caught  in  a  special  trough,  and  is  run  off.  The 
cloth  is  finally  washed  with  water  to  remove  all  the  soap. 

Mixed  goods,  called  "  unions,"  composed  of  cotton  warp  and  wool 
weft,  or  goods  made  of  two  kinds  of  wool,  will  "  cockle  "  or  wrinkle 
when  wet,  owing  to  unequal  shrinkage.  They  are  consequently 
"  crabbed,"  to  take  the  stretch  out  of  the  fibre.  The  cloth  is  passed 
through  a  bath  of  boiling  water,  and  at  once  rolled  tight  and  smooth 
on  a  roller  or  beam.  After  cooling  on  the  roll,  it  is  again  passed 
through  hot  water,  and  rewound  on  a  second  beam.  The  process 
is  repeated  a  third  time,  using  cold  water,  and  rolling  the  cloth  under 
heavy  pressure,  obtained  by  a  weighted  roller  resting  on  top  of  the 


456  OUTLINES  OF   INDUSTRIAL   CHEMISTRY 

beam.  In  order  to  stretch  the  goods  under  higher  temperatures 
than  they  will  be  subjected  to  in  the  subsequent  dyeing,  they  are 
next  steamed  by  rolling  them  on  a  perforated  iron  cylinder,  into 
which  steam  at  40  pounds  pressure  is  admitted  and  forced  through 
the  whole  thickness  of  the  cloth.  After  cooling,  it  is  rewound  on 
another  perforated  roll,  and  steamed  again.  This  rewinding  brings 
those  portions  of  the  cloth  which  were  on  the  outside  of  the  roll, 
into  the  centre  and  nearer  the  steam  entrance,  so  that  the  effect  of 
the  high  temperature  is  made  more  even  throughout  the  piece.  The 
goods  may  now  be  scoured  and  dyed  without  shrinkage,  provided 
that  the  temperature  in  these  processes  does  not  exceed  that  obtained 
in  the  crabbing  and  steaming. 

Wool  cannot  be  bleached  by  any  process  similar  to  that  used  for 
vegetable  fibre,  since  it  would  be  dissolved  by  the  lye-boils,  while 
chlorine  would  combine  with  the  fibre  without  destroying  the  natural 
yellow  color.  The  bleaching  agent  most  generally  used  is  sulphur 
dioxide,  or  its  solution  in  water  as  sulphurous  acid.  It  is  almost 
always  used  as  gas,  and  the  operation  is  called  "  stoving,"  sulphur- 
ing, or  gas  bleaching.  It  is  carried  on  in  a  closed  brick  chamber,  or 
"  stove,"  about  6x10x6  feet,  the  wooden  lining  of  which  is  made 
fast  by  wooden  pegs,  so  that  all  metal  (especially  iron)  is  excluded. 
The  washed  and  scoured  hanks  are  hung  on  wooden  rods,  for  6  or  8 
hours,  in  contact  with  the  sulphur  fumes  produced  by  burning 
sulphur  in  a  pot  in  the  bottom  of  the  stove.  Thin  cloth  is  stoved  by 
passing  it,  in  the  open  width,  in  a  zigzag  course  up  and  down  many 
times  over  rollers  at  the  top  and  bottom  of  the  chamber,  which  it 
finally  leaves  through  the  same  narrow  slit  at  which  it  enters.  It 
may  be  pass  3d  through  the  chamber  several  times,  until  sufficiently 
bleached. 

Sometimes  the  goods  are  soaked  for  24  hours  in  a  solution  of 
sulphurous  acid,  or  sodium  bisulphite  with  mineral  acid,  and  then 
wrung  and  washed. 

The  action  of  sulphur  compounds  in  bleaching  wool  is  not  entirely 
clear.  By  some  authorities,  the  sulphur  is  supposed  to  decompose 
the  water  present,  liberating  hydrogen,  which,  in  turn,  unites  with 
the  color  to  form  a  colorless  body.  By  others  it  is  thought  that  the 
sulphur  enters  into  combination  with  the  coloring  matter  to  form 
a  colorless  sulphite  compound.  But  whatever  the  actual  reaction, 
the  bleach  is  not  permanent,  and  after  some  time  the  yellow  color 
gradually  returns,  especially  if  the  goods  are  washed  with  soap 
or  alkalies. 

Hydrogen  peroxide  is  an  effective  but  expensive  bleaching  agent 


TEXTILE  INDUSTRIES  457 

for  wool.  Since  it  affords  a  permanent  bleach,  the  coloring  matter 
is  probably  oxidized  and  destroyed.  The  goods  are  soaked  at  15°  C. 
for  24  hours  in  a  3  per  cent  solution  of  hydrogen  peroxide,  contain- 
ing 2  per  cent  of  ammonia  (sp.  gr.  0.910).  Increasing  the  temper- 
ature hastens  the  process.  Hydrogen  peroxide  is  also  used  for 
bleaching  hair,  furs,  and  feathers. 

SILK   BLEACHING 

The  boiling  off  and  discharging  of  raw  silk  has  already  been 
considered  (p.  439).  It  is  often  subjected  to  various  mechanical 
treatments  to  increase  its  lustre,  e.g.  "  stretching,"  in  which  the 
hanks  are  given  a  series  of  violent  jerks  while  suspended  from  a 
fixed  peg ;  "  glossing,"  in  which  they  are  twisted  very  tight ;  or 
"lustring,"  by  steaming  them  while  in  a  state  of  great  tension. 

Silk  is  bleached  with  sulphur  dioxide,  or  with  hydrogen  peroxide, 
or  with  potassium  permanganate  and  sulphurous  acid.  The  stoving 
process,  similar  to  that  used  for  wool  bleaching,  is  repeated  several 
times,  the  silk  being  washed  between  each  operation.  It  is  then 
tinted  with  a  trace  of  some  blue  or  other  coal-tar  dye  to  make  it 
appear  a  clearer  white. 

Tussur  silk  is  hard  to  bleach,  and  cannot  be  decolorized  by  stov- 
ing. A  bath  of  barium  peroxide  in  water,  followed  by  dilute  hydro- 
chloric acid,  is  recommended  by  Tessie  du  Motay.  Ammoniacal 
hydrogen  peroxide  may  also  act  on  silk  as  on  wool.  But  at  best, 
tussur  silk  can  only  be  bleached  a  light  cream  color. 

MORDANTS 

A  mordant  is  a  substance  used  in  textile  dyeing  and  printing, 
either  to  fix  or  to  develop  the  color  on  the  fibre.  In  the  first  case,  it 
combines  with  the  fibre,  and  forms  a  body  having  affinity  for  color- 
ing matter ;  in  the  second,  it  becomes  an  essential  constituent  of  the 
color  when  deposited  on  the  fibre.  Metallic  mordants  are  abstracted 
from  aqueous  solution,  wholly  or  in  part,  by  the  fibre,  upon  which 
they  generally  deposit  metallic  hydroxides  or  basic  salts,  which  form 
color  lakes  in  the  dyeing  process. 

Mordants  are  either  of  mineral  or  of  organic  origin.  The  former 
comprise  the  common  mineral  acids,  and  salts  of  aluminum,  chro- 
mium, iron,  copper,  antimony,  and  tin,  and  to  a  lesser  degree  those  of 
manganese,  cobalt,  nickel,  uranium,  vanadium,  and  tungsten.  The 
organic  mordants  are  certain  organic  acids,  especially  acetic,  oxalic, 
tartaric,  citric,  lactic,  the  sulphated  ricinoleic  and  oleic  acids  forming 


458  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

Turkey-red  oil,  and  tannin  substances,  mainly  derivatives  of  gallic 
or  protocatechuic  acids.  Only  the  most  important  of  these  mordants 
can  be  mentioned  here. 

Aluminum  mordants  are  chiefly  the  acetate  or  "red  liquor" 
(p.  262),  sulphate  (p.  240),  and  the  alums  (p.  244).  The  chlorides 
and  nitrates  are  rarely  used.  Aluminum  salts  are  used  for  mor- 
danting cotton,  linen,  and  wool,  but  very  seldom  for  silk.  Alum 
and  normal  sulphate  do  not  readily  yield  alumina  to  cotton.  Basic 
sulphates  are  generally  used,  and  deposit  over  50  per  cent  of  their 
alumina  on  the  fibre,  when  it  is  steeped  in  them,  and  then  dried  and 
aged  in  a  warm  atmosphere.  Sometimes  the  fibre  is  first  soaked  in 
some  such  substance  as  tannic  acid,  Turkey-red  oil,  or  stannate  of 
soda,  which  forms  insoluble  compounds  with  the  alumina  of  the  basic 
sulphate,  or  precipitates  it  as  such  in  an  insoluble  form.  The  acetate 
is  only  used  for  Turkey-red,  and  the  alumina  is  fixed  by  the  evapora- 
tion of  acetic  acid  during  the  aging. 

Alum  and  neutral  sulphate  are  much  used  for  wool,  the  fibre 
decomposing  these  solutions  when  boiled  in  them,  and  retaining  the 
alumina  in  an  insoluble  form.  The  wool  fibre  is  both  acid  and  basic 
in  character,  dissociating  these  salts,  and  combining  with  both  the 
acid  and  the  base  of  the  salt.  This  reaction  is  most  complete  at  a 
boiling  temperature ;  but  for  the  best  results  the  salts  must  not  be 
decomposed  until  they  have  had  time  to  penetrate  into  the  fibre. 
Decomposition  is  retarded  by  using  tartrates  or  oxalates  in  con- 
junction writh  the  aluminum  sulphate;  these  probably  form  alu- 
minum tartrate  or  oxalate  by  double  decomposition,  and  the 
aluminum  is  slowly  given  up  to  the  fibre.  Acid  potassium  tartrate 
(cream  of  tartar)  has  the  best  effect,  but  free  sulphuric,  hydrochloric, 
or  oxalic  acids  also  retard  the  decomposition. 

Silk  is  very  seldom  mordanted  in  this  way,  as  the  lustre  would 
be  injured. 

Chromium  salts,  which  react  similarly  to  the  aluminum  salts,  are 
used  for  cotton,  linen,  and  wool.  With  these  are  included  the 
chromates  and  bichromates,  but  in  all  cases  chromic  oxide,  Cr2O3,  is 
fixed  on  the  fibre.  Chromic  acid  and  its  salts  act  here  as  oxidiz- 
ing agents,  and  are  themselves  reduced  to  chromic  oxide  before 
deposition. 

Cotton  and  linen  are  difficult  to  impregnate  with  chromium  salts. 
The  sulphates,  nitrates,  and  acetates  are  much  used  in  calico  print- 
ing, while  bichromates  and  alkaline  solutions  of  chromium  hydroxide 
are  used  in  dyeing  and  printing.  The  most  successful  method  of  mor- 
danting cotton  with  chromium  salts  is  that  proposed  by  H.  Koechlin. 


TEXTILE  INDUSTRIES  459 

The  cotton  is  soaked  in  the  solution  of  chromium  salt  (preferably 
basic  salt),  dried  and  passed  through  boiling  soda  solution ;  the  pro- 
cess is  repeated  until  the  goods  are  sufficiently  mordanted. 

Another  process  is  to  prepare  the  goods  with  tannin,  or  with 
Turkey-red  oil,  and  then  soak  them  in  the  chromium  solution ;  the 
fixing  is  done  in  cold  lime-water.  A  solution  of  basic  chromium 
acetate  is  used  for  cotton;  after  steeping  some  hours,  it  is  dried 
and  steamed  in  a  closed  chamber,  to  fix  the  chromium  oxide  on  the 
fibre. 

Wool  is  mordanted  with  chromium  fluoride,  chrome  alum,  or 
bichromate  (chromic  acid).  Chrome  alum  yields  the  largest  quan- 
tity of  chromium  to  the  fibre,  but  in  dyeing,  the  result  is  less  satis- 
factory than  with  bichromates.  The  addition  of  cream  of  tartar  to 
chrome  alum  is  an  improvement.  Chromium  fluoride  mordants  wool 
very  well,  being  easily  but  slowly  decomposed,  without  the  use  of 
tartrates.  A  little  oxalic  acid  is  generally  added.  The  chromic  acid 
thus  deposited  on  the  fibre  does  not  effect  the  feel  or  spinning  quali- 
ties of  the  wool,  while  the  hydrofluoric  acid  set  free  appears  to  have 
no  injurious  action  on  the  dye  or  goods. 

Potassium  bichromate  is  the  most  generally  useful  mordant  for 
wool,  yielding  fast  and  brilliant  colors  on  dyeing.  The  mordant  bath 
contains  potassium  bichromate  to  the  amount  of  2  to  4  per  cent  of 
the  weight  of  the  wool,  dissolved  in  water  equal  to  50  to  100  times 
the  weight  of  the  wool.  The  goods  are  boiled  in  this  for  one  or  one 
and  a  half  hours,  and  washed,  and  are  then  ready  for  dyeing. 
Sulphuric  acid  is  sometimes  added  to  the  mordant  bath  in  small 
amounts,  but  better  results  are  obtained  with  oxalic  acid  or  cream  of 
tartar,  which  reduce  part  of  the  bichromate  to  chromium  hydroxide 
on  the  fibre ;  by  treating  the  chromed  wool  in  a  bath  of  sodium 
bisulphite  the  reduction  is  more  complete.  An  excess  of  chromic 
acid  in  the  fibre  oxidizes  the  color,  deadening  it  when  dyed,  and  also 
weakens  the  fibre.  Such  "overchromed"  wool  is  said  to  be  greatly 
improved  by  reduction  of  the  bichromate  in  the  fibre  before  dyeing. 

The  nature  of  the  changes  which  take  place  in  mordanting  wool 
with  bichromate  has  been  much  studied,  but  is  not  yet  clearly 
proved.  The  work  of  Knecht,*  and  of  Kay  and  Bastow,  t  indicate 
that  the  potassium  bichromate  is  partly  dissociated  into  neutral 
chromate  and  chromic  acid:  — 

K2Cr2O7  =  K2Cr04  +  Cr03 , 

*  Journal  of  the  Society  of  Dyers  and  Colorists,  1888,  104;  and  1889,  186. 
Mbid.,  1887,  118. 


460  OUTLINES   OF  INDUSTRIAL   CHEMISTRY 

the  latter  being  absorbed  by  the  fibre,  while  the  neutral  chromate 
remains  in  the  bath.  This  chromic  acid  is  subsequently  reduced 
during  the  dyeing. 

Silk  is  sometimes  mordanted  with  basic  chromium  salts,  and 
potassium  bichromate  is  occasionally  used  as  an  oxidizing  agent  in 
dyeing  catechu  browns  and  logwood  blacks. 

Iron  salts  are  largely  used,  both  in  dyeing  and  printing,  and  on 
all  fibres.  Both  ferrous  and  ferric  salts  are  employed,  the  most  im- 
portant being  sulphates,  basic  sulphates  (nitrate  of  iron),  acetates, 
and  nitrates.  They  are  not  only  applied  as  mordants,  but  also  as 
oxidizing  and  weighting  materials  to  modify  the  shades  of  color,  or  to 
increase  the  stiffness  and  density  of  the  goods.  With  most  dyes,  iron 
salts  tend  to  "  sadden  "  or  darken  the  shade,  and  are  therefore  chiefly 
used  for  dark  colors,  especially  browns  and  blacks.  In  mordanting, 
the  iron  is  usually  fixed  on  the  fibre  as  hydroxide  or  tannate. 

Cotton  is  treated  with  ferrous  sulphate  (copperas,  p.  237),  after 
having  been  previously  steeped  in  tannin,  thus  precipitating  tan- 
nate of  iron  on  the  fibre.  Ferrous  acetate  (pyrolignite  of  iron, 
p.  263)  is  used  by  impregnating  the  fibre  with  the  solution,  drying, 
and  aging,  or  the  goods  may  be  passed  through  lime-water.  It  is 
also  used  with  tannin-prepared  cotton.  Nitrate  of  iron  (basic  sul- 
phate, p.  123)  is  generally  used  for  cotton,  which  is  merely  saturated 
in  the  solution,  and  then  passed  into  lime-water  or  sodium  carbonate 
solution,  the  process  being  repeated  until  sufficient  hydroxide  has 
been  deposited  on  the  fibre.  Iron  buff  is  produced  in  this  way. 
Sometimes  the  goods  are  prepared  with  tannin,  passed  through  the 
lime-water  to  form  calcium  tannate,  and  then  into  the  iron  solution. 
This  produces  ferric  tannate,  varying  in  color  from  brown  to  black. 

Wool  is  sometimes  mordanted  by  boiling  with  oxalic  acid  and 
copperas,  the  latter  chiefly  to  sadden  the  color ;  but  other  iron  salts 
are  not  used. 

Silks  are  extensively  treated  with  iron  salts  in  dyeing  blacks. 
The  pyrolignite  of  iron  is  chiefly  used  on  raw  silks  which  have  been 
previously  prepared  with  tannin,  preferably  chestnut  extract.  The 
silk  is  worked  in  a  warm  (60°  C.)  pyrolignite  of  iron  solution,  ex- 
posed to  the  air  for  a  short  time,  and  then  washed.  By  sufficient 
repetition  of  this  treatment  the  weight  can  be  increased  from  200  to 
300  per  cent  of  the  original  weight  of  the  silk.  Hard  water  greatly 
assists  this  process.  The  color  produced  is  a  bluish  black ;  the  lus- 
tre is  dulled,  but  is  restored  by  a  bath  of  very  dilute  hydrochloric 
acid,  to  which  a  little  olive  oil  has  been  added. 

Boiled-off  silk  is  weighted  and  dyed  by  the  use  of  nitrate  of  iron, 


TEXTILE  INDUSTRIES  461 

the  silk  being  worked  in  the  iron  liquor,  washed,  and  put  into  a  boil- 
ing soap  solution  composed  of  "boiled-off  liquor"  (p.  439),  olein 
soap,  and  a  little  soda  crystals.  This  precipitates  the  ferric  hydrox- 
ide. The  silk  is  then  washed  with  hard  water  (which  helps  fix  the 
iron),  and  the  whole  process  repeated  until  sufficient  iron  has  been 
deposited  on  the  fibre.  With  each  operation,  the  weight  of  the  silk 
is  increased  about  4  per  cent,  and  the  color  becomes  dark  brown, 
though  the  lustre  is  preserved.  This  weighted  and  mordanted  silk 
is  then  dyed  black. 

Eaw  silk  is  also  weighted  with  nitrate  of  iron  and  has  greater 
affinity  for  the  iron  salt  than  has  boiled-off  silk. 

Copper  salts  are  chiefly  used  as  oxidizing  materials  in  mordant- 
ing, acting  as  carriers  of  oxygen.  Copper  sulphate  (blue  vitriol, 
p.  239)  and  acetate  (verdigris,  p.  204)  are  most  used. 

Copper  sulphate  is  used  in  producing  logwood  blacks  and  cutch 
browns  on  cotton.  On  wool,  it  is  used  together  with  aluminum  sul- 
phate and  copperas  for  logwood  blues  and  blacks,  and  also  with 
potassium  bichromate.  Copper  salts  act  as  saddeners  for  logwood 
blacks  on  silk. 

Antimony  salts  used  as  mordants  are  tartar  emetic  (potassium 
antimony  tartrate),  double  oxalates  of  potassium  and  antimony,  and 
fluorides  of  antimony  and  sodium.  They  are  always  used  after  tan- 
nin mordanting  on  vegetable  fibre,  where  they  form  antimony 
tannates.  They  are  not  used  for  silk  or  wool.  Tartar  emetic  is 
generally  employed,  and  its  application  is  very  simple ;  the  tannin- 
mordanted  cotton  is  passed  at  once  into  a  cold  bath  of  the  salt,  and 
then  thoroughly  washed  before  drying. 

Tin  salts  are  valuable  mordants,  yielding  especially  brilliant 
shades.  The  salts  chiefly  used  are  stannous  chloride  (tin  crystals, 
SnCl2  •  2  H20),  stannic  chloride,  SnCl4,  sodium  stannate  ("  preparing 
salt,"  Na^SnOg),  and  stannous  nitrate,  Sn(N03)2  (known  only  in  solu- 
tion). "  Tin  sjjirits  "  is  a  general  name  for  a  number  of  tin  solutions 
of  various  composition,  made  with  nitric,  sulphuric,  or  oxalic  acid. 
By  dissolving  granulated  tin  in  concentrated  hydrochloric  acid,  a  so- 
lution of  stannous  chloride  is  formed,  which  is  sold  as  "muriate  of 
tin" ;  or  tin  crystals  are  separated  from  it,  and  the  mother-liquors, 
containing  a  large  amount  of  tin  chloride,  are  often  sold  as  muriate 
of  tin,  single  or  double,  according  to  the  strength.  "Pink  salt"  is  a 
double  stannic-ammonium  chloride,  SnCl4  -f  2  NH4C1,  formerly  much 
used  as  a  mordant.  Various  solutions  of  stannic  salts  were  much 
used  under  such  names  as  Cotton  Spirits,  Pink  Cutting  Liquor,  Oxy- 
muriate  of  Tin,  Solution  of  Tin,  etc. 


'\  B  R  A 


462  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

Cotton  and  linen  are  not  often  mordanted  with  stannous  salts, 
but  being  powerful  reducing  agents,  they  (especially  tin  crystals)  are 
used  by  the  calico  printer  in  "  discharges,"  or  "  resists."  Stannous 
chloride  reduces  iron  salts  and  is  used  to  neutralize  the  effect  of  iron 
impurities  in  calico  printing.  Stannic  salts  are  much  used  as  mor- 
dants on  cotton  and  linen,  when  these  are  dyed  with  natural  dye- 
stuffs,  such  as  camwood,  barwood,  fustic,  etc.,  and  for  some  of  the 
aniline  dyes.  Tannic  acid  is  used  before  the  tin,  and  stannic  oxide 
or  stannic  tannate  is  fixed  on  the  fibre.  Stannate  of  soda  is  also 
used  to  mordant  cotton  and  to  prepare  it  for  printing ;  the  goods  are 
steeped  in  the  solution  and  then  passed  into  a  bath  of  dilate  mineral 
acid  or  aluminum  sulphate,  which  precipitates  stannic  hydroxide  on 
the  fibre. 

Wool  is  often  mordanted  with  stannous  chloride  by  entering  it  in 
a  cold  bath  of  about  4  per  cent  tin  crystals  (calculated  on  the  weight 
of  the  wool)  and  2  per  cent  oxalic  acid  or  cream  of  tartar.  This  is 
then  slowly  heated  to  boiling.  Too  much  tin  salt  makes  the  wool 
harsh  and  prevents  proper  felting  in  the  milling  process.  Stannic 
chloride  is  not  a  suitable  mordant  for  wool,  but  impure  mixtures  of 
stannic  and  stannous  salts  are  often  used  as  mordants  for  cochineal 
scarlets  on  wool.  Wool  is  sometimes  prepared  with  sodium  stannate 
for  printing,  followed  by  treatment  with  dilute  sulphuric  acid. 

Black  silks  are  weighted  with  stannous  chloride  together  with 
catechu,  on  fibre  which  has  already  been  weighted  with  iron.  For 
weighting  light-colored  silks,  stannic  chloride  (tin  spirits)  is  often 
used.  The  raw  fibre  is  steeped  in  a  solution  of  tin  salt  until  im- 
pregnated, and  the  tin  hydroxide  is  fixed  by  treatment  with  cold  di- 
lute soda  solution,  or  by  merely  washing  in  water.  The  silk  is  then 
"  boiled-off  "  in  soap  liquor  to  remove  the  harsh  feel.  The  weight  is 
increased  about  25  per  cent  by  this  process.  But  stannic  chloride 
has  an  injurious  action  on  the  fibre  if  too  strong  (over  50°  Tw.)  and 
shrinks  it  very  much,  besides  destroying  certain  dyes  which  may  be 
afterwards  used. 

Acetic  acid  (p.  261)  is  largely  used  in  dyeing  and  printing,  but 
more  as  an  assistant  than  a  mordant.  It  neutralizes  many  bases 
without  affecting  the  dyeing  process,  and  it  does  not  attack  vegeta- 
ble fibre  under  any  conditions.  Crude  pyroligneous  acid  contains 
reducing  substances,  and  because  of  this  is  used  where  oxidation  is 
to  be  prevented. 

Oxalic  acid,  H2C204  •  2  H20,  forms  crystals  readily  soluble  in 
water.  It  is  largely  used  in  dyeing,  mainly  as  an  addition  to  the 
dye-bath  to  retard  the  deposition  of  the  color,  and  for  a  fixing  agent 


TEXTILE   INDUSTRIES  463 

in  mordanting  wool  with  bichromate,  aluminum  sulphate,  or  cop- 
peras. 

Tartaric  acid,  C2H2(OH)2(COOH)2,  is  often  used  as  an  addition  to 
the  mordant  bath  for  wool,  and  to  the  d}^e-bath  to  retard  the  dyeing, 
and  in  clearing  and  brightening  the  color  on  silk  after  dyeing ;  also 
as  a  "  resist "  and  "  discharge  "  in  calico  printing.  The  most  im- 
portant tartrates  are  cream  of  tartar,  C4H404(OH)  •  (OK),  and  tartar 
emetic,  C4H406K  -  (SbO)  +  £  H20. 

Citric  acid,  C3H4(OH)(COOH)3,  and  lactic  acid,  C2H4(OH)COOH, 
(p.  415),  are  used  somewhat  in  place  of  tartaric  acid,  but  more 
especially  as  resists,  etc.,  in  calico  printing. 

Turkey-red  oil  (p.  312),  or  soluble  oil,  is  used  as  a  mordant  on 
cotton  for  dyeing  with  basic  dyes  and  Turkey-reds,  and  for  preparing 
cloth  for  calico  printing. 

TANNINS 

Tannins,  many  of  which  are  used  in  tanning,  are  also  very  impor- 
tant mordants,  their  value  here  depending  upon  the  fact  that  they 
are  readily  absorbed  by  cotton,  linen,  and  silk,  while  they  retain  their 
property  of  precipitating  insoluble  metallic  compounds  in  the  fibre, 
and  also  of  uniting  with  the  basic  dyes.  They  may  be  divided  into 
two  classes :  (a),  those  related  to  gallic  acid  (trioxyberizoic  acid), 
and  (6),  those  related  to  protocatechuic  acid  (dioxybenzoic  acid). 
When  heated,  the  former  yield  pyrogallol,  and  the  latter,  pyrocate- 
chin  (orthodioxy benzene).  Tannic  acid  is  the  most  important  of  the 
tannins.  It  is  a  digallic  acid,  C6H2  (OH),  •  CO2  -  C6H2  (OH)3 .  C02H. 
It  is  soluble  in  six  parts  cold  water,  and  is  obtained  by  extracting 
powdered  gall-nuts  with  water,  alcohol,  and  ether.  On  evaporation 
the  aqueous  solution  yields  the  tannin  as  a  colorless,  or  light  yellow, 
amorphous,  scaly,  or  vitreous  mass.  Tannic  acid  is  precipitated  from 
aqueous  solution  by  dilute  sulphuric,  or  hydrochloric  acid,  by  alka- 
lies, chlorides,  etc.,  but  not  by  nitric  acid,  or  Glauber's  salt.  Gela- 
tine or  untanned  hide  removes  it  completely  from  solution.  It  is  a 
weak  acid,  but  will  decompose  alkali  carbonates.  It  is  easily  oxid- 
ized, and  reduces  many  metallic  salts,  Fehling's  solution,  and  per- 
manganates. It  forms  a  blue-black  precipitate  with  ferric  salts,  and 
belongs  to  group  (a),  above  mentioned. 

The  tannins  occur  in  numerous  plants,  being  found  in  the  roots, 
bark,  wood,  leaves,  flowers,  fruit,  seed-pods,  or  in  excrescences  on  the 
plant.  The  chief  commercial  sources  are  gall-nuts,  sumach,  oak  and 
hemlock  bark,  mimosa  bark,  chestnut  wood,  cutch  (catechu),  gambier, 
myrabolans,  valonia,  divi-divi,  kino,  quebracho,  and  canaigre. 


464  OUTLINES  OF   INDUSTRIAL  CHEMISTRY 

Galls,  or  nut-galls,  are  excrescences  on  various  kinds  of  oak  trees, 
produced  by  the  sting  of  the  female  gall  wasp,  Cynips  gallon  tinctorice, 
Oliv.,  and  in  which  the  eggs  are  deposited.  Young  nut-galls,  from 
which  the  insect  has  not  yet  escaped,  are  greenish  or  bluish  in  color, 
and  are  very  rich  in  tannin;  afterwards  they  become  yellow,  and 
the  percentage  of  tannin  is  very  much  decreased.  The  best  qualities 
come  from  Persia,  but  the  Levant  galls,  from  Smyrna  and  Tripoli, 
contain  from  55  to  60  per  cent  tannic  acid  and  some  gallic  acid. 
Poorer  grades  come  from  Italy,  France,  Germany,  and  Austria. 

Japanese  and  Chinese  galls  are  caused  by  the  sting  of  an  insect 
(plant  louse)  on  the  leaves  of  plants  (Rlius  semialata,  Murr.)  of  the 
sumach  family.  These  galls  are  very  irregular  in  shape,  and  are 
light  and  hollow,  but  contain  70  per  cent  tannin,  or  even  more. 

Sumach  of  commerce  consists  of  the  leaves  and  young  twigs  from 
various  plants  of  the  Hhus  family,  especially  Rlius  Coriaria,  L. ; 
poorer  grades  are  derived  from  R.  Cotinus,  L.  These  shrubs  are 
found  in  many  countries,  but  Italy,  Spain,  Greece,  and  Virginia  fur- 
nish the  better  grades.  Sumach  is  largely  used  in  mordanting,  since 
it  contains  very  little  coloring  matter  to  stain  the  goods.  Good  sam- 
ples contain  from  15  to  20  per  cent  of  tannin,  and  are  sold  as  a  fine 
powder,  or  as  leaves,  mixed  with  twigs  and  stems.  Much  is  now  sold 
as  "  extract,"  a  thick  brown  liquid  obtained  by  evaporating  the  aque- 
ous solution,  usually  in  vacuum. 

Catechu,  or  cutch  (terra  japonica),  is  obtained  from  the  wood  and 
pods  of  Acacia  Catechu,  Willd.,  and  from  the  betel  nut,  the  fruit 
of  the  Areca  Catechu,  L.,  a  species  of  palm-tree.  Both  plants  are 
natives  of  India.  Cutch  appears  in  commerce  as  dark  brown,  irregu- 
lar lumps,  which  dissolve  in  water,  forming  a  dark  brown  solution. 
It  contains  a  tannin  called  catechu-tannic  acid,  and  another  body, 
catechin.  It  is  extensively  used  as  a  brown  dye  on  cotton,  for  calico 
printing,  and  also  in  the  weighting  of  black  silks.  It  is  a  good  mor- 
dant for  certain  basic  coal-tar  dyes,  when  employed  in  dyeing  com- 
pound shades.  On  cotton,  copper  salts  should  always  be  used  in 
conjunction  with  cutch. 

Gambler  is  extracted  from  the  leaves  of  an  Indian  shrub,  Uncaria 
dasyoneura,  Korth.  It  has  a  yellow  color,  and  is  used  somewhat  as 
a  pigment  and  as  a  yellow  dye.  It  is  slightly  soluble  in  cold  water, 
and  very  readily  so  in  hot  water.  In  commerce  it  appears  as  small 
cubical  blocks,  containing  about  40  per  cent  tannin,  chiefly  as  cate- 
chu-tannic acid.  Gambier  is  used  in  silk  and  cotton  dyeing,  much 
in  the  same  way  as  catechu.  It  is  extensively  used  in  tanning  Mo- 
rocco leather. 


TEXTILE  INDUSTRIES  465 

Myrabolans  are  the  dried  fruit  of  certain  Indian  and  Chinese 
trees,  Myrobolanus  Chebula,  Gsert.  They  appear  in  commerce  as 
dried  and  shrivelled  nuts  about  an  inch  long,  containing  about  30 
per  cent  tannin  (ellagitannic  acid),  and  also  a  brownish  coloring 
matter.  They  are  used  in  place  of  tannic  acid,  for  some  purposes  in 
mordanting  cloth,  and  also  in  weighting  black  silks. 

Valonia  is  the  acorn  cups  of  an  oak,  Quercus  ^Egilops,  L.,  native 
of  Greece,  Asia  Minor,  and  France.  The  cups  are  very  large,  and  cov- 
ered with  coarse  hair,  or  "  beard,"  which  is  especially  rich  in  tannin. 
They  are  drab  in  color,  and  contain  a  yellow  coloring  matter.  Good 
valonia  contains  about  30  per  cent  of  true  tannic  acid. 

Divi-divi  is  the  fruit  of  a  West  Indian  tree,  Ccesalpinia  coriaria, 
"Willd.  It  forms  very  thin  pods  about  three  inches  long,  and  often 
folded  and  twisted,  and  containing  about  30  per  cent  of  ellagitannic 
acid,  with  some  gallic  acid.  The  color  of  the  pods  varies  from  light 
brown  to  black,  and  considerable  coloring  matter  is  present,  which 
stains  the  goods.  It  is  used  for  mordanting  blacks  on  cotton  and  silk. 

Chestnut,  Castanea  saliva,  Mill.,  furnishes  a  tannin  extract,  the 
composition  of  whose  tannin  is  unknown.  The  extract  is  a  black 
solid,  or  a  brown  syrup,  forming  turbid  solutions  with  water.  It  is 
very  extensively  used  in  weighting  black  silk. 

Kino  is  the  dried  sap  of  certain  trees,  Pterocarpus  Marsupiurrij 
Roxb.,  Butea  frondosa,  Roxb.,  and  Eucalyptus  rostrata,  Schlecht.  It 
forms  small  garnet-red  angular  grains,  slightly  soluble  in  water,  and 
contains  a  large  quantity  of  kinotannic  acid,  a  substance  of  unknown 
composition.  The  chief  supplies  come  from  India,  Africa,  and 
Australia.  It  is  chiefly  used  in  medicine,  and  resembles  catechu. 

Oak  and  hemlock  bark  are  rich  in  tannins,  containing  about  15 
per  cent,  but  they  are  contaminated  with  certain  anhydride  substances 
which  are  slightly  soluble  in  water,  and  color  the  goods  a  deep  brown 
or  red,  and  hence  are  unsuitable  for  mordants.  These  anhydrides 
are  called  phlobaphenes,  and  are  much  like  the  tannins  in  their  action, 
combining  with  fibre  and  precipitating  gelatine,  ferric  salts,  etc. 
These  barks  are  extensively  used  for  making  leather,  especially 
the  heavy  and  strong  kinds. 

Mimosa  bark  is  obtained  from  several  species  of  Acacia  in  Aus- 
tralia. It  contains  about  24  per  cent  tannins,  which  are  derivatives 
of  protocatechuic  acid. 

Quebracho  is  an  extract  made  from  hardwood  trees,  Aspidosperma 
Quebracho,  Schlecht,  and  Quebrachia  Lorentzii,  Griseb.,  natives  of 
South  America.  It  contains  about  25  per  cent  of  tannins,  contami- 
nated with  red  coloring  matter. 


466  OUTLINES  OF  INDUSTRIAL   CHEMISTRY 

Canaigre  is  obtained  from  the  roots  of  a  species  of  dock,  Mumex 
hymenosepjtlus,  Torr.,  a  native  of  Arizona  and  New  Mexico.  It  is 
now  extensively  cultivated  in  the  southwestern  part  of  the  United 
States.  It  contains  about  30  per  cent  of  tannin,  together  with  a 
bright  yellow  coloring  matter,  much  resembling  gambier.  It  is 
always  sold  as  extract. 

Extracts  are  now  prepared  from  nearly  all  of  the  above  tannin 
substances,  by  treating  them  with  water  and  evaporating  the  tannin 
solution  to  a  thick  syrup,  or  even  to  dryness,  generally  by  the  aid  of 
vacuum.  These  extracts  are  much  more  economical  to  ship,  and 
more  convenient  to  use,  but  are  frequently  adulterated  with  glucose 
or  other  matter. 

COLORING    MATTERS 

NATURAL   DYESTUFFS 

Natural  dyestuffs  have  been  employed  for  textile  coloring  since 
prehistoric  times.  They  are  soluble  in  water  and  have  more  or  less 
tendency  to  combine  directly  with  the  fibres.  Many  of  them  are 
not  in  themselves  dyes,  but  form  color  lakes  by  combination  with 
mordants.  In  recent  years  they  have  been  very  generally  replaced 
by  the  more  brilliant  and  readily  applied  artificial  colors. 

Indigo  is  one  of  the  oldest  known  dyes,  and  probably  originated 
in  India.  It  exists  in  the  indigo  plant,  Indigofera  tinctoria,  L.,  and 
in  woad,  Isatis  tinctoria.,  L.,  in  the  form  of  a  glucoside,  indican, 
C26HS1N017,  which  is  decomposed  by  acids  to  form  the  coloring  prin- 
ciple indigotine,  C16H10N202,  and  a  sugar.  To  isolate  the  coloring 
matter,  the  stems  and  leaves  of  the  plant  are  put  into  a  cemented 
cistern  and  covered  with  water.  A  fermentation  soon  begins,  caus- 
ing a  rise  in  the  temperature,  while  the  indican  is  decomposed  and 
the  sugary  matter  destroyed ;  at  the  same  time,  the  indigo  is  reduced 
to  indigo  white,  C16H12N202.  This  dissolves  to  form  a  greenish- 
yellow  liquid,  which  is  drawn  off  into  vats  and  violently  stirred  and 
splashed  by  the  workmen  for  several  hours,  in  order  to  thoroughly 
aerate  and  oxidize  the  indigo  white.  The  blue  pigment  precipitates, 
and  after  settling,  the  liquor  is  drained  off.  The  magma  is  re- 
peatedly washed  and  finally  boiled,  to  prevent  any  further  fermenta- 
tion, and  is  filtered,  drained  in  cloth-lined  frames,  and  finally  pressed 
into  cakes ;  these  are  carefully  dried,  away  from  the  sunlight.  The 
yield  is  about  0.2  to  0.3  per  cent  of  the  weight  of  the  plant. 

The  indigo  of  commerce  forms  dark  blue  cubical  cakes  having 
a  matt,  earthy  appearance  on  the  fractured  surface.  Its  content 


TEXTILE  INDUSTRIES  407 

of  pure  indigo  varies  from  20  to  90  per  cent  and  averages  about 
45  per  cent.  It  contains  indigo  red  and  indigo  brown,  which  affect 
the  shade  of  the  blue;  also  moisture  and  mineral  and  glutinous 
substances.  Indigo  is  tasteless,  odorless,  insoluble  in  water,  alcohol, 
ether,  dilute  acids  or  alkalies.  By  careful  heating  it  sublimes.  If 
very  finely  powdered,  concentrated  and  fuming  sulphuric  acid  dissolve 
it  to  form  mono-  and  disulphonic  acids,  the  latter  being  soluble  in 
water.  The  sodium  salts  of  these  indigo  sulphonic  acids  constitute 
the  indigo  extract,  soluble  indigo,  or  indigo  carmine  of  commerce.* 
These  are  obtained  by  neutralizing  the  sulphuric  acid  solution  of 
indigo  with  sodium  carbonate,  and  precipitating  the  indigo  carmine 
by  adding  common  salt.  True  indigo  carmine  is  the  sodium  salt  of 
the  disulphonic  acid,  and  is  dyed  on  animal  fibres  as  an  acid  dye, 
p.  484;  when  sold  as  a  dry  powder  it  is  called  "indigotine." 

For  methods  of  indigo  dyeing,  see  p.  489. 

Logwood  is  the  heart  wood  of  a  tropical  tree,  Hcematoxylon 
Campecliianum,  L.,  native  in  Central  America.  It  is  brought  in 
commerce  in  the  form  of  logs,  chips,  and  extract.  The  chromogen 
(p.  479)  in  the  wood  is  hcematoxylin,  C16H1406,  which  forms  nearly 
colorless  crystals  when  pure;  it  exists  in  the  wood  as  a  glucoside 
and  partly  in  the  free  state.  It  is  readily  oxidized,  especially  in  the 
presence  of  an  alkali,  to  form  haematein,  C16H1206,  which  is  the  real 
dyestuff.  This  forms  colored  lakes  with  metallic  bases,  yielding 
violets,  blues,  and  blacks  with  the  various  mordants. 

The  logs  are  chipped  or  rasped  to  form  a  coarse  powder,  which 
does  not  contain  much  haematein  when  fresh,  the  dyestuff  being 
formed  by  "curing"  or  oxidizing.  The  rasped  wood  is  fermented 
by  moistening  with  water  and  exposing  in  heaps  to  the  air.  To 
control  the  temperature  and  give  better  exposure,  the  heap  is 
shovelled  over  and  sprinkled  with  water  at  frequent  intervals,  until 
the  chips  assume  a  deep,  reddish-brown  color,  or  even  develop  a 
bronze  shade.  Alkalies,  potassium  nitrate,  chalk,  or  ammonium 
chlorate  are  sometimes  added  to  hasten  the  process.  The  cured 
chips  yield  a  decoction  which  is  rapidly  taken  up  by  the  fibre  in 
dyeing  operations.  The  amount  of  water  in  cured  ,chips  is  nearly 
double  that  contained  in  the  fresh  wood. 

Most  "  extract "  of  logwood  is  now  made  from  chips  which  are 
not  cured.  They  are  put  into  an  extractor,  an  iron  vessel  provided 

*  Artificial  indigo  is  made  from  orthonitrophenylpropiolic  acid,  by  heating  with 
caustic  soda  solution  in  the  presence  of  a  reducing  substance,  such  as  glucose.  This 
method  is  only  used  in  certain  forms  of  calico  printing,  the  blue  being  thus  developed 
directly  on  the  fibre.  But  the  cost  of  natural  indigo  is  still  less  than  that  of  the 
artificial  product. 


468  OUTLINES  OF  INDUSTRIAL   CHEMISTRY 

with  a  false  bottom  and  a  perforated  steam  coil.  The  extractors 
are  often  set  in  batteries,  so  arranged  that  the  liquor  from  one  flows 
into  the  next  more  recently  filled  vessel,  finally  leaving  that  con- 
taining the  freshest  wood.  Pressure  extraction  is  often  used,  but  an 
increase  of  over  15  pounds  is  liable  to  cause  decrease  in  the  coloring 
power  of  the  product.  After  settling  to  separate  wood  fibre  and 
resin,  the  liquid  from  the  extractors  is  evaporated  in.  vacuum  pans, 
the  Yaryan  being  often  used  for  the  dilute  liquors.  When  it  becomes 
thick,  the  evaporation  is  continued  in  a  common  vacuum  pan 
(strike  pan)  until  a  density  of  about  50°  Tw.  is  reached  for  liquid 
extract ;  or  it  may  be  continued  until  a  solid  extract  is  obtained  011 
cooling.  Throughout  the  process,  precautions  are  taken  to  prevent 
access  of  air  and  consequent  oxidation  of  the  product.  The  use  of 
chemicals  to  develop  the  color  in  the  extract  itself  is  of  doubtful 
value,  as  this  development  should  only  take  place  in  the  dye-bath. 
The  yield  of  solid  extract  is  about  20  per  cent  with  pressure,  and 
without  pressure  about  16  per  cent. 

Logwood  extract  is  frequently  adulterated  with  glucose,  molasses, 
and  chestnut,  hemlock,  and  quercitron  extracts.  Logwood  is  chiefly 
used  with  a  chrome  or  iron  mordant  for  blacks  on  wool  and  cotton. 

Red  woods  of  commerce  are  Brazil  wood,  Ccesalpmia  Bmsiliensis, 
L.,  and  Pernambuco  wood  (C.  Crista,  L.),  from  Brazil,  West  Indies, 
and  Bahama ;  sappan  wood,  C,  Sappan,  L.,  from  China,  Japan,  and 
Siam;  Lima  wood,  C.  bijuga,  Sw.,  from  Central  America;  and  peach 
wood,  (7.  ecliinata,  Lam.  These  contain  the  chromogen  bmsilin, 
C16H14O5,  which  is  chemically  related  to  hsematoxylin.  Brasilin  is 
colorless,  but  dissolves  in  alkalies,  forming  a  red  solution  which 
oxidizes  on  exposure  to  the  air,  forming  brasilein,  CwH^Oa;  this 
combines  with  alumina  to  form  red  lake  similar  to  alizarin  red,  but 
more  fugitive. 

Another  class  of  red  woods  contains  santalin  (C15H1405).  These 
resemble  Brazil  woods  in  color,  but  are  heavier  and  of  harder  text- 
ure. The  more  common  ones  are  sandal  wood,  Pterocarpus  santa- 
linus,  L.,  from  Madagascar  and  the  East  Indies ;  bar  wood,  Baphia 
nitida,  Lodd.,  and  camwood. 

Madder  is  the  pulverized  root  of  Rubia  tinctorum,  L.,  a  plant 
formerly  largely  cultivated  in  Europe  and  Asia  Minor.  It  contains 
glucosides  which  are  decomposed  by  fermentation,  forming  alizarin, 
C14H602(OH)2,  and  purpurin,  C14H502(OH)3,  which  are  identical  with 
di-  and  trioxyanthrachinon.  Madder  extract  is  prepared  by  fer- 
mentation and  evaporation  of  the  filtered  solution,  yielding  "gar- 
ancine  "  and  "  madder  flowers." 


TEXTILE   INDUSTRIES  469 

Madder  has  been  used  for  ages  in  dyeing  Turkey-red  on  cotton, 
affording  one  of  the  brightest  and  fastest  colors.  But  in  1868, 
Grsebe  and  Liebermann  made  artificial  alizarin  from  anthracene 
derived  from  coal-tar.  In  consequence  of  this  discovery,  the  madder 
industry  has  nearly  disappeared. 

Archil  or  orseille  (cudbear)  is  an  important  dyestuff  derived 
from  certain  lichens,  Roccella  tinctoria,  D.  C.,  E.  fuciformis  (L.)  D.  C., 
indigenous  in  Madagascar,  Zanzibar,  Azores,  Ceylon,  and  France,  and 
Lecanora  tartarea,  Achar.,  from  Sweden.  They  contain  mixtures  of 
phenols  and  phenol  acids,  which,  when  treated  with  ammonia  and 
exposed  to  the  air,  yield  orcein,  a  violet  powder  sold  as  "cudbear." 
It  is  either  a  paste  or  powder  prepared  by  evaporating  the  aqueous 
extract  to  dryness  in  vacuum.  The  powder  dissolves  in  alkalies 
and  forms  colored  lakes  with  heavy  metals  and  lime.  It  was  for- 
merly much  used  in  wool  dyeing,  yielding  violet  and  red  shades. 

Litmus  is  obtained  by  treating  the  above  mentioned  lichens  with 
ammonia  and  potash,  and  fermenting  the  mass.  The  dyestuff  forms 
a  red  color-acid,  whose  alkali  salts  are  blue.  The  commercial  article 
consists  of  calcium  carbonate,  or  sulphate,  which  is  mixed  with  the 
coloring  matter  and  formed  into  small  cubes.  It  is  not  used  as  a 
dye,  but  is  interesting  because  of  its  use  as  an  indicator. 

Cochineal  consists  of  the  dried  bodies  of  the  female  insects, 
Coccus  cacti.  These  insects  live  on  certain  cactus  plants  in  Mexico, 
Central  America,  Algeria,  and  the  East  Indies ;  they  are  collected, 
and  killed  by  placing  them  in  ovens  or  in  hot  water,  or  by  steaming 
them.  When  killed  by  dry  heat,  the  cochineal  is  coated  with  a 
silvery  gray  powder,  consisting  of  a  wax,  coccerin;  but  if  boiled  or 
steamed,  the  cochineal  is  "  black,"  and  of  less  tinctorial  power.  The 
silver  gray  is  often  imitated  by  dusting  the  black  cochineal  with 
powdered  stearic  acid  or  talc.  The  coloring  principle  is  carminic 
acid,  C17H180IO,  a  glucoside,  soluble  with  a  deep  red  color  in  water, 
and  forming  scarlet  lakes  with  alumina  and  tin  salts.  Cochineal 
contains  about  10  per  cent  carminic  acid.  The  dye  is  chiefly  used 
on  wool.  Cochineal  yields  the  pigment  carmine  (p.  212). 

Lac  dye  is  also  obtained  from   an   insect,    Coccus  lacca,  which 

exudes  the  lac  resin  (p.  344).     The  collection  and  preparation  of  the 

resin  involves  the  preparation  of  the  dye.     The  latter  is  very  similar 

to  carminic  acid,  and  is  prepared  by  extracting  the  gum  with  sodium 

'  carbonate. 

Kermes  is  similar  to  cochineal,  and  consists  of  dried  insects, 
Coccus  ilicis,  from  northern  Africa  and  Spain.  It  is  seldom  used  in 
dyeing  at  the  present  time. 


470  OUTLINES   OF  INDUSTRIAL   CHEMISTRY 

Fustic  is  the  heart  wood  of  Chlorophora  tinctoria,  Gaud.,  or 
Madura  tinctoria  native  in  West  Indies  and  tropical  South  America. 
It  yields  a  coloring  principle,  morin,  C12H805,  which  forms  lemon 
yellow  lakes  with  alumina.  It  is  sold  as  chips,  and  as  an  extract, 
and  is  chiefly  used  for  wool  dyeing,  especially  for  modifying  the 
shade  of  logwood,  and  other  dyes. 

Young  fustic  is  the  heart  wood  of  a  sumach,  Rlius  CQtinus,  L., 
native  in  Spain,  Italy,  Hungary,  and  the  Levant.  It  yields  an 
orange-colored  lake  with  alumina  and  tin.  The  color  principle  is  a 
glucoside,  fustin. 

Quercitron  is  the  powdered  bark  of  the  North  American  tree, 
Quercus  coccinea,  var.  tinctoria,  Gray.  It  contains  a  dyestutf,  quer- 
citrin,  C^M^Oso,  which  is  converted  by  dilute  acid  into  quercetin, 
C^H^On,  and  isodulcit,  C6H1406.  Quercetin  dissolves  in  alkali  with 
a  yellow  color,  and  forms  yellow  lakes  with  alumina  and  tin.  By 
extracting  the  bark  with  alkali,  and  neutralizing  the  extract  with 
sulphuric  acid,  a  mixture  of  quercitrin,  quercitin  and  isodulcit  is 
obtained,  which  appears  in  commerce  as  "flavine."  Both  the  bark 
and  the  extract  are  used  in  wool  dyeing  and  calico  printing. 

Persian  berries  are  the  dried  fruit  (berries)  of  certain  buckthorn 
(Rhamnus)  species,  growing  throughout  southern  Europe.  The  col- 
oring principle  is  a  glucoside,  which  is  decomposed  by  acids  into 
isodulcit  and  rhamnetin,  Ci2H1005 ,  the  latter  being  the  dyestuif .  It 
forms  yellow  and  orange  shades  with  alumina  and  tin,  arid  is 
mainly  used  in  calico  printing. 

Curcuma,  or  turmeric,  is  the  dried  root  of  various  species  of 
Curcuma  of  Central  Asia.  The  dyestuif  is  curcumin,  C14H1404,  which 
yields  a  tolerably  fast  yellow  on  cotton.  It  is  also  used  to  color 
oils,  and  wax. 

Annatto  (arnotto)  is  obtained  from  the  fruit  of  the  West  Indian 
and  South  American  trees,  Bixa  Orellana,  L.  It  contains  the  orange 
dye,  bixin,  C28H3405 ,  and  comes  in  commerce  as  a  thick  paste,  or  dry 
cakes.  It  is  mainly  used  for  coloring  butter  and  cheese. 

dutch  is  described  on  p.  464. 

ARTIFICIAL   DYESTUFFS 

The  artificial  organic  dyestuff  industry  originated  in  England 
with  the  discovery  of  the  lilac  color,  mauve,  by  Perk  in,  in  1856. 
This  was  obtained  by  direct  oxidation  of  aniline  containing  toluidine. 
In  1859  Verguin  made  magenta,  or  fuchsine,  and  each  following 
year  other  colors  were  discovered,  until  at  the  present  time  there  are 
several  thousand  dyes  on  the  market,  and  a  stupendous  industry  has 


TEXTILE  INDUSTRIES  471 

arisen  in  their  manufacture.  Because  the  first  dyes  were  prepared 
from  aniline,  the  colors  were  known  as  "aniline  dyes/'  a  name 
still  applied  to  them  as  a  class,  but  they  are  more  generally  called 
"coal-tar  dyestuifs."  They  are  derived  from  various  substances, 
most  of  which  are  derivatives  of  aromatic  bodies,  especially  those 
of  benzene,  naphthalene,  and  certain  pyridine  bases,  particularly 
quinoline. 

The  limits  of  this  book  will  not  permit  a  full  consideration  of 
the  individual  dyestuffs,  and  recourse  must  be  had  to  the  numerous 
handbooks  mentioned  in  the  references. 

The  coal-tar  colors  may  be  divided  into  the  following  groups  * :  — 

I.  Aniline,  or  Amine  dyes. 

(a)   Eosaniline  derivatives. 
(6)    Safranines  and  Indulines. 

(c)  Oxazines. 

(d)  Thionines  (sulphur  compounds). 

(e)  Aniline  black. 

II.  Phenol  dyes. 

(a)   Nitro  bodies. 
(6)   Nitroso  bodies. 

(c)  Phthaleins  and  Indophenols. 

(d)  Rosolic  acid. 

III.  Azo  dyes. 

IV.  Quinoline  and  acridine  derivatives. 
V.   Anthracene  dyes. 

VI.   Artificial  Indigo. 

I.  The  aniline  or  amine  dyes  include  all  those  which  contain 
derivatives  of  nitrogenous  bases,  excepting  only  the  azo  colors. 

(a)  The  rosaniline  group  contains  derivatives  of  amido-triphenyl 
methane,  in  which  three  benzene  rings  are  attached  to  the  same  car- 
bon atom.  The  hydrogen  of  the  amido  groups  may  be  replaced  by 
other  radicals,  and  thus  the  structure  of  the  individual  dyes  becomes 
very  complex.  These  substances  are  made  from  aniline  or  its  homo- 
logues. 

The  most  important  dyes  of  this  group  are  the  following :  — 

Magenta,  or  fuclisine,  consists  of  rosaniline  and  para-rosaniline 
hydrochlorides,  and  is  made  by  oxidizing  aniline  containing  toluidine 
with  nitrobenzene ;  formerly  arsenic  acid  or  mercuric  chloride  was 
used  as  the  oxidizing  agent. 

*  After  Beuedikt-Knecht,  Chemistry  of  Coal-Tar  Colors. 


472  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

Add  magenta,  or  fachsine  S,  is  an  alkali  salt  of  tlie  trisulphonic 
acid  of  ordinary  magenta. 

Methyl  violet,  or  Paris  violet,  is  a  salt  of  pentamethyl-para-rosani- 
line,  made  by  oxidizing  dimethyl-aniline  with  copper  chloride. 

Methyl  green  is  formed  from  methyl  violet  by  the  action  of  methyl 
chloride. 

Alkali  blue,  or  Nicholson's  blue,  is  the  sodium  salt  of  the  mono- 
sulphonic  acid  of  triphenyl-rosaniline  blue,  which  latter  is  formed  by 
the  action  of  aniline  upon  para-rosaniline,  in  the  presence  of  oxalic 
or  benzoic  acids. 

Benzaldehyde  green,  or  malachite  green,  is  made  by  heating  dimethyl- 
aniline  with  benzaldehyde  in  the  presence  of  fused  zinc  chloride. 

Acid  green,  or  Helvetia  green,  is  the  sodium  salt  of  the  monosul- 
phonic  acid  of  benzaldehyde  green. 

Auramine  is  a  yellow  dye  made  by  treating  dimethyl-aniline  with 
phosgene  (COC12),  and  heating  the  product  to  150°  C.  with  ammonium 
chloride  and  zinc  chloride. 

(6)  The  safranines,  indulines,  and  nigrosines  are  basic  dyes  which 
are  not  of  similar  composition,  but  are  derived  from  the  same  sub- 
stances. 

Safranine  is  made  by  oxidizing  a  mixture  of  one  molecule  of  a 
diarnine  (e.g.  para-phenylenediamine,  C6H4(NH2)2)  and  two  molecules 


/  /3  x 

of  a  monamine  (  e.g.   toluidine,   C6H4^  .     The  dye  comes  in 

NNH,' 
commerce  as  the  chlorhydrate  of  the  color  base. 

Magdala  red  (naphthalene  red)  is  made  by  heating  amidoazonaph- 

C10H7N 
thalene,  II  ,  with  the   hydrochloride   of   a-naphthylamiue, 


C10H7NH2  •  HC1.     It  is  chiefly  used  in  silk  dyeing. 

Mauvein  (mauve)  is  made  by  oxidizing  aniline  containing  tolui- 
dine, with  chromic  acid.  It  is  the  first  aniline  color  that  was  made. 

Induline  (indigo  substitute,  fast  blue)  is  made  by  heating  amido- 
azobenzene  with  aniline.  The  product  is  rendered  soluble  by  con- 
version into  a  sulphonate. 

Nigrosine  is  a  bluish-gray  dye  made  by  heating  aniline-chlor- 
hydrate  with  nitrophenol. 

(c)  Oxazines  are  represented  by  cotton  blue,  prepared  by  treating 
/?-naphthol  with  nitrosodimethyl-aniline  hydrochloride  ;  gallocyanine, 
made  by  treating  gallic  or  tannic  acid  with  nitrosodimethyl-aniline 
hydrochloride;  Nile  blue,  made  by  the  action  of  nitrosodimethyl- 
meta-amidophenol  on  a-naphthylamine. 


TEXTILE  INDUSTRIES  473 

(d)  Thionines  are  dyes  containing  sulphur,  and  are  made  from 
para-ainido  bodies.    The  most  important  dye  of  this  class  is  methylene 
blue,  tetramethyl-thionine  chloride,  made  by  treating  nitrosodimethyl- 
aniline  with  hydrogen  sulphide,  and  oxidizing  with  ferric  chloride. 

(e)  Aniline  black  is  of  unknown  composition.     It  is  always  pro- 
duced directly  upon  the  fibre  by  methods  given  on  p.  491. 

II.  The  phenol  dyes  contain  hydroxyl  groups,  imparting  acid 
properties  to  the  dyestuff. 

(a)  Nitro  dyes  are,  for  the  most  part,  yellow  dyes  having  a 
strong  acid  character.  By  reduction  in  acid  solution,  they  yield 
colorless  amido  compounds. 

Picric  acid  is  trinitrophenol  made  by  nitrating  either  pure  car- 
bolic acid  or  phenyl-sulphonic  acid.  It  forms  yellow,  scaly  crystals, 
and  is  used  in  silk  and  wool  dyeing.  Its  alkali  salts  are  explosive. 

Victoria  yellow  is  made  by  treating  para-toluidine,  C6H4  •  CH3  •  NH2, 
or  para-cresol,  C6H4  •  CH3  •  OH,  with  nitric  acid. 

Naphthol  yellow  (Martins  yellow)  is  the  sodium,  potassium,  or  lime 
salt  of  dinitro-tt-naphthol.  It  yields  a  gold  yellow  on  silk  and  wool, 
but  is  volatile  when  slightly  heated. 

Naphthol  yellow  S  is  made  by  nitrating  a-naphthol  trisulphonic 
acid,  C10H4(S03H)3OH  by  which  two  of  the  sulphonic  acid  radicals 
are  replaced  by  nitro  groups.  It  is  much  faster  than  the  preceding 
dye. 

Aurantia  is  made  by  nitrating  diphenylamine  or  methyl-diphenyl- 
aniine,  CH3  •  N(C6H5)2.  The  commercial  dye  is  the  ammonium  salt. 

(6)  Nitroso  bodies  produced  by  the  action  of  nitrous  acid  on 
phenols  yield  coloring  matters;  only  those  derived  from  resorcin 
are  important. 

Resorcin  blue  is  the  ammonium  salt  of  tetrabromresorufin.  Ee- 
sorcin  is  treated  with  nitrous  acid  to  form  nitrosoresorcin,  which 
combines  with  more  resorcin  in  the  presence  of  sulphuric  acid  to 
form  resorunn.  This  is  then  treated  with  bromine. 

(c)  Phthaleins  are  produced  from  phthalic  acid  or  its  anhydride 
by  combining  with  phenols.  The  products  are  derivatives  of  tri- 
phenyl-methane,  and  a  number  of  very  important  dyes  are  found  in 
this  group. 

Phenol-phthale'in  is  produced  by  the  moderate  heating  of  two 
molecules  of  phenol  with  one  molecule  of  phthalic  anhydride.  It 
is  only  used  as  an  indicator  in  alkalimetry. 

Fluorescein,  derived  from  resorcin  and  phthalic  anhydride,  is  the 
base  of  the  important  eosins.  The  sodium  salt  of  fluorescein  is  the 


474  OUTLINES  OF  INDUSTRIAL   CHEMISTRY 

dyestuff  uranin.  Eosins  are  the  halogen  derivatives  of  fluoresce'in  ; 
the  eosin  yellow  shade,  or  eosin  G,  is  the  sodium  salt  of  tetrabrom- 
fluorescei'n  ;  eosin  B,  or  erythrosin,  is  the  alkali  salt  of  tetraiodofluo- 
rescei'n  ;  rose  Bengale  is  the  tetraiododichlorfluorescei'n  ;  $)liloxin  is  the 
tetrabromdichlorfluorescein  These  dye  brilliant  pinks  having  a 
yellow  fluorescence,  on  silks  and  wools. 

Rhodamine  is  made  by  heating  phthalic  anhydride  with  diethyl- 


I,  C«H/ 

XOH 


2H5)2 


meta-amidophenol,  C6H4<  .     It  dyes   a  brilliant  pink   on 

XOH 

wool  and  silk,  and  is  comparatively  fast  to  light,  a  property  lacking 
in  the  eosins. 

Oalle'in  is  the  phthale'in  of  pyrogallol,  and  when  heated  with 
strong  sulphuric  acid  forms  the  olive  green  dye  called  coerulein, 
belonging  to  the  azo  dyes.  It  is  very  fast  when  used  with  a  chro- 
mium mordant. 

Indophenol  is  made  by  oxidizing  a  phenol  and  a  para-diamine, 
particularly  a-naphthol  and  dimethyl-para-phenylenediamine.  It 
yields  shades  resembling  indigo  on  cotton  and  wool,  and  may  be 
reduced  by  glucose  and  caustic  soda  to  a  colorless  indophenol  white, 
which  oxidizes  in  the  air  to  again  form  the  blue ;  hence  it  is  much  used 
in  indigo  vats  to  brighten  and  cheapen  the  vat  indigo  colors. 

(d)  Rosolic  acids  are  made  from  rosaniline  or  para-rosaniline  by 
treating  with  sodium  nitrite,  and  then  boiling  with  sulphuric  acid. 
This  forms  rosolic  acid,  or  aurin,  which  are  red  dyes  of  unstable 
character. 

III.  Azo  dyes.  These  contain  the  chromophor  —  N :  N  — .  They 
are  all  prepared  by  treating  diazo  compounds  with  amines  or  phenols 
of  the  aromatic  series.  The  dyes  are  amido  or  hydroxyl  compounds 
of  the  azo  bodies,  and  three  groups  are  distinguished :  the  amidoazo 
dyes,  amidoazosulphonic  acids,  and  the  oxyazo  dyes. 

(a)  Amidoazo  dyes. 

Chrysoidine  is  diamidoazobenzene  hydrochloride, 

C6H5N:N.C6H8(]SrH2)2.HCl, 

and  is  made  by  adding  a  solution  of  meta-phenylenediamine  to  "a 
solution  of  diazobenzene  chloride.  It  yields  a  brownish-orange  color 
on  silk,  wool,  and  tannin-mordanted  cotton. 

Bismarck  brown,  or  phenylene  brown,  is  triamidoazobenzene 
hydrochloride,  and  is  made  by  the  action  of  nitrous  acid  on  meta- 
phenylenediamine.  It  is  much  used  for  leather  dyeing,  and  for 


TEXTILE  INDUSTRIES  475 

wool,  and  cotton  mordanted  with  tannin,  yielding  a  full  brown 
shade. 

(6)  Amidoazosulphonic  acids. 

Fast  yellow,  acid  yellow,  is  the  sodium  salt  of  amidoazobenzene, 
disulphonic  acid.  It  is  much  used  for  dyeing  compound  shades  in 
acid  baths  with  acid  magenta,  indigo  extract,  etc.,  and  for  making 
other  diazo  colors. 

Methyl  orange,  helianthin,  orange  III,  is  made  by  the  action  of 
dimethyl-aniline  on  diazobenzene-sulphonic  acid.  Its  formula  is 

(CH3)2K  •  C6H4  -  N  :  N  -  C6H4 .  S03Na. 

It  is  used  in  acid  bath  for  dyeing  silk  and  wool,  and  as  an  indicator 
in  volumetric  work. 

Tropceolin  00,  diphenylamine  orange,  is  made  by  treating  diazo- 
benzene-sulphonic acid  with  diphenylamine,  and  is  used  to  dye  silk 
and  wool  a  golden  yellow. 

Metanil  yellow  is  made  by  the  action  of  diphenylamine  upon  meta- 
amido-benzene-sulphonic  acid. 

(c)  Oxyazo  dyes. 

The  primary  aromatic  amines,  when  diazotized,  will  combine  with 
phenols  and  phenol  derivatives,  forming  azo  dyes.  The  number  in 
this  group  is  therefore  very  large,  many  shades  of  yellow,  orange, 
red,  and  brown  being  known.  When  amidoazo  compounds  are  di- 
azotized, secondary  azo  bodies  are  formed ;  they  contain  two  of  the 
chromophor  groups  —  N  :  N  — ,  and  form  one  class  of  the  tetrazo 
group. 

Orange  G  is  the  sodium  salt  of  diazobenzene-/3-naphthol-disul- 
phonic  acid. 

Azococcin  2  R  is  made  by  treating  diazoxylene  hydrochloride  with 
tt-naphthol-monosulphonic  acid.  It  is  a  red  color  used  in  silk  dyeing. 

Wool  scarlet  R  is -made  by  treating  diazoxylene  hydrochloride 
with  tt-naphthol-disulphonic  acid. 

Scarlet  2  R,  Ponceau  2  R,  xylidine  redt  is  made  by  the  action  of 
/?-naphthol-disulphonic  acid  upon  diazo-meta-xylene  hydrochloride. 
It  is  much  used  in  the  place  of  cochineal. 

Scarlet  3  R,  Ponceau  3  R,  cumidine  red,  is  made  by  treating  diazo- 
meta-cumene  with  /3-naphthol-disulphonic  acid. 

Fast  red  A,  Roccelline  is  made  by  treating  /3-naphthol  with  a-diazo- 
naphthalene  sulphonic  acid.  It  is  much  used  instead  of  orchil  or 
barwood. 

Fast  red  B,  Bordeaux  B,  is  obtained  from  diazonaphthalene  hy- 
drochloride and  /3-naphthol-disulphonic  acid. 


476  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

Of  the  secondary  diazo  colors  (tretrazo  dyes)  the  following  are 
important. 

Cloth  red  G  is  made  by  treating  diazotized  amido-azotoluene  with 
/?-naphthol-sulphonic  acid.  It  is  used  to  replace  red  woods  in  dyeing 
and  is  fast  to  light  and  milling  when  dyed  on  a  chromium  mordant. 

Crocein  scarlet  3  B,  Ponceau  4RB,  is  formed  by  the  action  of 
diazotized  amidoazobenzene-monosulphonic  acid  upon  /J-naphthol- 
sulphonic  acid.  It  is  much  used  for  wool  dyeing. 

Brilliant  crocein,  cotton  scarlet,  is  made  by  treating  diazotized 
amido-azobenzene  with  /?-naphthol-y-disulphonic  acid.  It  is  the 
purest  and  brightest  of  the  scarlets  and  is  used  on  cotton,  wool,  and 
silk.  It  is  fast  to  light  and  milling. 

Biebrich  scarlet,  Ponceau  3  R  B,  is  made  from  diazotized  amidoazo- 
benzene-sulphonic  acid  and  /8-naphthol.  It  is  an  acid  dye  used  on 
silk  and  wool  for  shades  similar  to  cochineal. 

Wool  black  is  formed  by  the  action  of  diazotized  amidoazoben- 
zene-disul phonic  acid  on  para-tolyl-/?-naphthylamine.  It  dyes  a  deep 
blue  black  which  is  fairly  stable. 

Naphthol  black  B,  brilliant  black,  is  prepared  from  amidoazo- 
naphthalene-disulphonic  acid  and  /J-naphthol-disulphonic  acid. 
Naphthol  blacks  8  B  and  6  B  are  similar.  They  are  chiefly  used  in 
wool  dyeing. 

The  class  of  tetrazo  dyes  derived  from  benzidine,  tolidine,  and 
stilbene  has  become  very  important,  since  they  color  unmordanted 
vegetable  fibres  ;  also,  many  of  them  act  as  mordants  for  other  coal- 
tar  dyes. 

Congo  red,  first  made  in  1884,  was  the  first  of  these  dyes  to 
appear.  It  is  made  by  treating  diazotized  benzidine  with  two  mole- 
cules of  a-naphthylamine-sulphonic  acid ;  its  formula  is 

C6H4  -  N  :  N  -  C10H5(NH2)  •  S03Na. 
C6H4  -  N  :  N  -  C10H5(NH2)  .  S03Xa. 

It  dyes  Turkey-red  shade  on  cotton,  which  is  fast  to  washing, 
but  the  slightest  trace  of  acid  changes  it  to  blue, 

Benzopurpnrin  4B  is  made  from  diazotized  ortho-toluidine  and 
/3-naphthylamine-sulphonic  acid.  Benzopurpurin  6  B,  deltapurpu- 
rin,  and  rosazurin  B  are  similar  dyes.  These  all  yield  red  shades 
on  cotton  and  wool. 

Benzoazurin  is  made  from  diazotized  dianisidine  and  a-naphthol- 
sulphonic  acid.  It  dyes  a  blue  shade,  and  may  be  used  with  other 
dyes  for  mixed  shades  and  in  dyeing  mixed  goods. 


TEXTILE  INDUSTRIES  477 

Chrysamine  is  a  yellow  dye  produced  from  tetrazo-diphenyl,  or 
ditolyl,  chlorides  and  salicylate  of  soda.  Its  formula  is :  — 

C6H3(CH3)  -  N  :  N  -  C6H3(OH)  .  COONa. 
C6H3(CH3)  -  N  :  N  -  C6H3(OH)  .  COONa. 

It  is  used  for  cotton  dyeing  and  also  for  mixed  goods  ("unions  "). 

Azo-blue  is  produced  by  the  action  of  tetrazo-ditolyl  chloride  on 
/J-naphthol-sulphonate  of  soda.  It  is  not  fast  to  light. 

Hessian  purples  are  produced  by  the  action  of  diazotized  diamido- 
stilbene-disulphouic  acid  upon  various  aromatic  amines  and  phenols. 
These  resemble  the  benzidine  dyes,  and  are  applied  011  cotton  in  a 
soap  biith  or  with  salt  and  acetic  acid. 

Mikado  dyes  are  made  by  treating  glycerine  or  other  oxidizable 
substances  in  alkaline  solution,  with  para-nitrotoluene-sulphonic  acid. 

Primuline  is  a  yellow  dye  made  by  the  action  of  sulphur  on  para- 
toluidine  and  sulphonating  the  product.  By  treating  cotton,  dyed 
with  primuline  in  a  diazotizing  bath,  and  then  passing  into  an  alka- 
line solution  of  phenols,  various  yellow,  red,  or  brown  shades  are 
formed  on  the  fibre  ("  ingrain  colors  "). 

IV.  Quinoline  and  acridine  derivatives  furnish  several  important 
dyes. 

Quinoline  yellow  is  made  by  heating  quinaldine,  C10H9N,  with 
phthalic  anhydride  and  zinc  chloride,  and  then  sulphonating  the 
product.  It  yields  pure  yellow  shades  on  wool  and  silk  in  acid 
baths. 

Flavaniline  is  made  by  heating  acetanilide  with  zinc  chloride  to 
250°  to  270°  C.  for  several  hours.  The  color  is  converted  into  the 
hydrochloride,  which  is  a  basic  dye  applied  to  cotton  (mordanted) 
and  wool  or  silk.  The  shade  is  a  greenish  yellow. 

Photphine  or  chrysaniline  is  produced  as  a  by-product  in  making 
magenta  by  the  arsenic  acid  process.  The  commercial  dye  is  the 
nitrate  of  diamidophenylacridine,  and  is  chiefly  used  in  silk  dyeing 
and  for  leather  coloring. 

V.  The  anthracene  colors,  although  not  very  numerous,  are  all 
mordant  dyes,  the  alizarins  being  distinguished  by  their  fastness  to 
soap,  acids,  chlorine,  and  light,  surpassing  in  this  respect  nearly  all 
the  other  natural  or  artificial  dyes.     They  all  contain  free  hydroxyl 
groups,  are  insoluble  in  water,  but  dissolve  in  caustic  alkalies. 


478  OUTLINES  OF  INDUSTRIAL   CHEMISTRY 


Alizarin  is  dioxany  thraquinone,  C6H4<          >C6Hjj(OH)2,  and  is  the 

XCOX 

coloring  principle  of  madder  (p.  468).     It  is  made  artificially  by 

/CHv 

oxidizing  anthracene,  C6H4\         /C6H4  to  form  anthraquinone,  the 

XX 


sulphonic  acid  of  which  is  then  fused  with  caustic  soda  and  potas- 
sium chlorate.  If  anthraquinone  monosulphonic  acid  is  employed, 
alizarin  (blue  shade)  is  obtained  ;  with  a-disulphonic  acid,  Jlavopur- 
purin,  and  with  /3-acid,  anthrapurpurin  is  formed,  each  of  these 
being  a  trioxyanthraquinone. 

Alizarin  is  brought  into  commerce  usually  as  a  paste  with  water, 
containing  20  per  cent  of  the  dyestuff.  Its  color  principles  have 
been  described  in  connection  with  madder  (p.  468).  It  sublimes,  and 
forms  orange-red  crystals.  Anthrapurpurin  (isopurpurin)  is  isomeric 
with  the  pur  pur  in  of  madder.  Flavopurpurin  forms  yellow  needles 
melting  above  330°  C.  Commercial  alizarin  is  a  mixture  of  alizarin, 
anthrapurpurin,  and  flavopurpurin,  a  large  percentage  of  the  last  two 
yielding  the  alizarin,  yellow  shade,  or  alizarin  G.  By  treating  the 
ordinary  alizarin  with  fuming  sulphuric  acid,  it  is  converted  into  a 
monosulphonic  acid,  whose  sodium  salt  constitutes  the  alizarin  S  of 
commerce.  It  is  soluble  in  water,  and  is  used  for  wool  dyeing  only. 
Its  shades  are  similar  to  those  produced  by  ordinary  alizarin. 

Anthracene  brown,  or  anthragallol,  is  made  by  heating  gallic  acid 
with  phthalic  anhydride  and  zinc  chloride,"  or  with  benzoic  acid  and 
concentrated  sulphuric  acid.  It  is  isomeric  with  anthrapurpurin, 
etc.,  and  yields  various  shades  of  brown  with  metallic  mordants. 
The  color  is  fast  to  light  and  milling. 

Alizarin  orange  is  /?-nitroalizarin,  made  by  acting  on  alizarin, 
blue  shade,  with  nitrous  acid.  It  yields  orange  shades  with  alumina, 
and  red-violet  with  iron.  It  is  mainly  used  as  a  steam  color  in  calico 
printing. 

Alizarin  blue  is  made  by  heating  /3-nitroalizarin  with  glycerine 
and  sulphuric  acid.  It  is  sold  as  a  paste,  and  is  mainly  used 
as  a  steam  color  in  calico  printing.  It  may  be-  reduced  and  rendered 
soluble,  and  used  as  a  vat  dye  similar  to  indigo.  By  mixing 
the  paste  with  sodium  bisulphite  solution,  and  allowing  it  to  stand 
some  days,  a  water  soluble  color,  alizarin  blue  S,  is  formed,  which 
is  very  fast  to  light,  and  has  generally  replaced  the  insoluble 
blue. 

Alizarin  green  S  is  produced  by  treating  alizarin  blue  with  fuming 


TEXTILE   INDUSTRIES  479 

sulphuric  acid.     It  produces  green  shades  of  blue  on  wool,  which  are 
fast  to  milling. 

Alizarin  black  S  is  the  sodium  bisulphite  compound  of  dioxynaph- 
thoquinone.  It  is  made  by  treating  a-dinitronaphthalene  with  zinc 
and  concentrated  sulphuric  acid,  and  then  combining  the  product  with 
sodium  bisulphite.  It  is  used  on  wool,  mordanted  with  potassium 
bichromate,  for  various  shades  of  slate  and  black.  The  colors  are 
fast  to  light. 


VI.  Artificial  indigo  (see  p.  467).  A  dyestuff  sold  as  "im 
salt"  is  a  sodium  bisulphite  compound  of  orthonitrophenyl-lacto- 
methylketone,  which  is  soluble  in  water.  When  applied  to  cotton, 
and  the  goods  then  passed  through  caustic  soda  liquor,  a  deep  indigo 
blue  is  developed. 

DYEING 

Dyeing  is  the  process  of  precipitating  coloring  matter  upon  or 
within  the  substance  of  a  body  by  chemical  action.  Dyestuffs  are 
distinguished  from  pigments  by  the  fact  that  they  are  soluble  in 
water,  or  in  the  liquid  of  the  dye-bath,  from  which  solution  they  are 
abstracted  by  the  material  to  be  dyed.  In  the  vast  majority  of  cases 
dyes  are  applied  to  textile  fibres  or  fabrics,  but  occasionally  natural 
products,  such  as  straw,  feathers,  horn,  leather,  ivory,  bone,  or  wood, 
may  be  dyed.  The  substance  is  immersed  in  a  hot  or  cold  aqueous 
solution  of  the  dyestuff,  except  in  a  few  rare  cases,  where  other  solv- 
ents than  water  may  be  used,  or  the  solution  applied  as  a  spray.  The 
solution  may  be  neutral,  acid,  or  alkaline,  according  to  the  nature  of 
the  material  and  of  the  dyestuff ;  thus  alkaline  or  neutral  baths  are 
generally  used  for  cotton  and  vegetable  fibres,  neutral  or  acid  baths 
for  wool,  and  acid  or  alkaline  baths  for  silk. 

Dyestuffs  are  sometimes  spoken  of  as  substantive  and  adjective ; 
the  former  will  color  fibres  directly,  the  latter  will  only  color,  with 
any  permanence,  when  used  in  conjunction  with  a  mordant.  Nietzki 
designates  the  two  classes  as  direct  dyes  and  mordant  dyes.  Hum- 
mel *  divides  coloring  matters  into  monogenetic,  or  those  which  pro- 
duce only  one  color  under  any  condition ;  polygenetic,  those  which 
produce  several  colors,  according  to  the  mordant  used. 

The  artificial  coal-tar  dyes  have  been  very  carefully  studied,  and 

the  theory  of  the  relation  of  color  to  constitution  proposed  by  Witt 

is  generally  accepted.     He  shows  that  by  the  introduction  of  certain 

groups  (called  ehromophores)  into  colorless  aromatic  hydrocarbons, 

*  Dyeing  of  Textile  Fabrics,  p.  147. 


480  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

colored  substances  (called  chromogens)  are  produced.  These  chro- 
mogens  possess  very  slight  coloring  powers  in  themselves,  but  are 
converted  into  dyestuffs  by  the  addition  of  certain  salt-forming 
("auxochrornous")  groups,  such  as  hydroxyl  (OH),  or  the  aniido 
group  (NH2).  The  salts  formed  are  of  a  deeper  color  than  the  free 
dyestuif.  Thus,  benzene  is  colorless,  but  the  introduction  of  chro- 
mophorous  groups,  such  as  the  nitro  group  (N02),  or  the  azo  group 
(— N  =  N— ),  forms  the  feebly  colored  chrornogens,  mono-,  di-,  and 
tri-nitrobenzene  and  azobenzene.  The  chromogens,  in  turn,  may 
take  up  the  auxochromous  groups  (OH)  or  (NH2),  and  form  dye- 
stuffs  such  as  picric  acid,  C6H2  (N02)3  (OH),  or  amidoazobenzeiie, 
C6H5N=NC6H4  »NH2.  If  the  auxochromous  groups  are  converted 
into  salts  the  color  is  much  intensified;  thus  sodium  picrate  is  a 
much  darker,  deeper  yellow  than  picric  acid.  But  the  sulpho-group, 
S03H,  and  the  carboxyl  group,  C02H,  are  not  auxochromous,  not- 
withstanding that  they  form  salts,  since  they  impart  very  little 
tinctorial  power  to  the  chromogens.  From  this  Witt  drew  the  fol- 
lowing conclusions :  — 

1.  The  simultaneous  occurrence  of  a  chromophor  and  an  auxo- 
chromous group  is  essential  to  the  development  of  tinctorial  proper- 
ties in  an  aromatic  substance. 

2.  The  chromophor  exerts  a  greater  color-generating  influence  in 
the  salt-like  derivatives  of  the  dyestuff  than  in  the  free  compounds. 

3.  In  the  case  of  dyes  of  similar  constitution,  the  one  having  the 
more  stable  salts  is  the  better. 

The  theory  of  dyeing  has  not  yet  been  clearly  elucidated.  The 
mechanical  theory  assumes  the  coloring  to  be  due  to  a  mechanical 
absorption  of  particles  of  coloring  matter  into  the  pores  of  the  fibre ; 
the  chemical  theory  supposes  a  chemical  combination  to  take  place 
between  the  coloring  matter  and  some,  or  all,  of  the  constituents  of 
the  fibre.  By  the  former  theory,  the  cause  of  the  inability  of  many 
dyes  to  color  all  fibres  equally  well  is  ascribed  to  the  difference  in 
the  size  of  the  dye  molecules,  or  of  the  pores  of  the  various  fibres. 
Further,  the  pores  are  supposed  to  expand  by  heat,  or  by  the  action 
of  certain  chemicals,  and  to  contract  by  cold  or  by  astringent  sub- 
stances. The  chemical  theory  is  supported  by  the  facts  that  textile 
fibres  are  either  acid,  or  acid  and  basic  in  character,  and  have  the 
power  of  absorbing  and  retaining  alkalies,  acids,  and  some  salts ;  and 
further,  that  all  coloring  matters  have  either  an  acid  or  basic  charac- 
ter. Between  these  two  theories  is  Witt's  solid  solution  theory; 
this  supposes  that  fibres  extract  coloring  matters  from  aqueous  solu- 
tion in  much  the  same  way  that  ether  withdraws  certain  bodies  from 


TEXTILE  INDUSTRIES  481 

their  aqueous  solutions,  the  fibres  thus  acting  as  solid  solvents  for 
the  dyes.  However,  it  seems  probable  that  with  wool  and  silk  the 
process  is  truly  chemical ;  but  with  cotton  and  other  vegetable  fibres, 
which  have  a  totally  different  composition  from  the  animal  fibres,  the 
question  is  not,  as  yet,  definitely  decided. 

The  methods  of  dyeing  and  composition  of  the  dye-bath  depend 
essentially  upon  the  nature  of  the  fibre  and  of  the  dye.  As  a  rule 
silk  and  wool  are  dyed  directly,  although  mordants  are  used  in  some 
cases.  Cotton  and  linen  have  much  less  affinity  for  coloring  mat- 
ters ;  and,  with  the  exception  of  certain  coal-tar  dyestuffs  of  the  ben- 
zidine  class  and  the  related  primuline  derivatives  (ingrain  colors),  a 
mordant  is  always  used. 

The  character  of  the  water  is  of  much  importance  in  dyeing. 
The  most  injurious  impurity  is  iron,  since  this  dulls  (saddens)  the 
shade  of  most  colors.  A  hard  water,  containing  lime  or  magnesium 
salts,  should  generally  be  purified  before  use,  though  in  a  few  cases, 
notably  in  Turkey-reds  and  in  dyeing  with  logwood,  the  presence 
of  lime  is  necessary.  Suspended  matter  must  be  removed. 

Stone  dye-vats  were  formerly  much  used,  but  these  are  now 
largely  replaced  by  iron  tanks.  Or,  for  certain  delicate  colors, 
especially  on  silk,  the  tanks  are  made  of  wood,  so  put  together  that 
no  iron  shall  come  in  contact  with  the  dye  liquors,  and  copper  steam 
pipes  are  used  for  heating.  Hanks  to  be  dyed  are  suspended  from 
sticks  laid  across  plain,  open  tanks,  provided  with  false  bottoms, 
under  which  steam  is  introduced.  Since  this  involves  much  hand 
labor  in  turning  the  hanks,  many  machines  have  been  devised,  in 
which  the  hanks  are  usually  weighted  at  the  lower  end  by  rollers 
to  keep  them  -straight,  and  are  suspended  on  rollers  of  wood  or 
porcelain,  which  are  rotated  by  suitable  driving-gear.  Or  they  are 
fixed  on  sticks  on  the  periphery  of  a  rotating  drum,  which  is  partly 
submerged  in  the  dye-bath;  the  apparatus  is  enclosed  in  a  wooden 
case  to  confine  the  steam  and  heat,  and  to  prevent  too  much  cooling 
of  the  yarn  while  not  submerged.  Sometimes  yarn  is  dyed  in  warps 
and  in  the  "  cops  "  formed  on  the  spinning-frames,  but  the  machines 
for  such  dyeing  are  too  complicated  for  description  here. 

A  large  part  of  dyeing  operations  are  done  on  piece  goods,  for 
which  machines  are  generally  used.  A  simple  vat,  with  a  winch 
placed  above  it,  is  very  often  used.  The  pieces  (previously  sewed 
together  to  form  an  endless  band)  are  made  to  pass  continuously 
through  the  liquor,  a  certain  amount  of  slack  being  allowed,  to 
increase  the  time  of  exposure  to  the  dye.  The  goods  pass  through 
2i 


482  OUTLINES  OF   INDUSTRIAL   CHEMISTRY 

the  bath  several  times,  until  the  desired  shade  is  obtained.  The 
most  common  machine  for  cotton  goods  is  the  "jigger."  In  this 
two  rolls  are  placed  in  the  bottom  of  the  vat,  and  three  guide  rolls 
at  the  top.  The  cloth,  unwinding  from  a  beam  above  the  machine, 
passes  in  the  open  width  over  the  first  top  roll,  into  the  dye  liquor 
and  under  the  first  submerged  roll ;  it  then  ascends  to  the  middle 
roll  at  the  top  of  the  vat  and  again  passes  down  under  the  second 
submerged  roll,  from  which  it  goes  out  of  the  dye,  over  the  third 
guide  roll,  and  is  wound  on  a  second  beam.  The  machine  is  then 
reversed  and  the  cloth  run  back,  over  and  under  the  rolls  to  the 
first  beam.  When  dyed,  the  goods  are  drawn  on  to  the  "  batch 
roll,"  from  which  they  are  soon  run  through  the  washing  machine. 

For  mordanting  and  dyeing  cotton  cloth  in  the  piece,  "padding 
machines"  are  much  used.  This  consists  of  a  small  vat  or  tank, 
above  which  are  squeeze-rolls  to  remove  the  excess  of  liquor,  and 
the  goods  are  consequently  less  likely  to  become  uneven  in  color  by 
further  action  of  the  absorbed  dye  liquor  while  on  the  "  batch  roll." 
Padding  machines  with  large  rolls  have,  to  a  great  extent,  replaced 
jiggers  for  cotton  dyeing. 

Dyes  may  be  grouped,  according  to  the  method  of  application, 
into  five  classes :  — 

1.  Direct  dyes,  which  yield  full  colors,  without  the  assistance 
of  mordants. 

2.  Basic  dyes,  which  form  insoluble  tannates  and  require  mor- 
dants on  vegetable  fibres,  but  dye  animal  fibres  without  mordants. 

3.  Acid  dyes,  which  require  no  mordant  on  animal  fibres,  but 
which  find  only  a  limited  use  for  vegetable  fibres. 

4.  Mordant   dyes,  which   require   a   metallic  mordant  on  both 
animal  and  vegetable  fibres. 

5.  Special  dyes,  which  can  only  be  applied  to  or  developed  in 
the  fibre  by  special  processes. 

1.  The  direct  dyes  comprise  the  beuzidine  dyes  (Congo,  diamine, 
Hessian,  and  benzo  colors),  and  certain  ingrain  colors  derived  from 
primuline  and  from  some  of  the  benzidine  dyes,  by  diazotizing  the 
amido  groups  after  dyeing  on  the  fibre,  and  then  "  developing  "  the 
color  by  treating  with  phenols,  naphthols,  or  amines.  Being  very 
soluble,  they  are  prone  to  "  bleed  "  when  the  goods  are  washed,  but 
owing  to  this  same  fact  they  are  very  easy  to  dye  evenly  ("  level ") 
on  the  goods.  They  are  applied  to  all  fibres  without  mordants, 
generally  in  neutral  or  alkaline  baths ;  the  addition  of  a  little  acetic 
acid  renders  them  fast  to  milling  on  wool.  Some  substance  called 


TEXTILE  INDUSTRIES 

an  "  assistant "  is  usually  added  to  the  dye-bath  to  accelerate,  retard, 
or  modify  the  deposition  of  the  color ;  but  this  does  not  enter  into 
combination  with  the  color  (or  with  the  mordant  when  used  with 
basic,  acid,  or  other  dyes). 

The  assistants  used  for  direct  dyes  are  common  salt,  Glauber's 
salt,  sodium  phosphate,  borax,  soda,  or  soap;  these  are  added  in 
amounts  varying  from  5  to  20  per  cent.  They  render  the  dye  less 
soluble  and  cause  a  more  complete  precipitation  on  the  goods,  or 
retard  the  deposition  by  increasing  the  solubility. 

Cotton  is  dyed  with  the  direct  dyes  in  a  boiling  bath,  usually 
with  from  10  to  15  per  cent  common  salt  or  Glauber's  salt.  The 
ingrain  colors  are  obtained  by  dyeing  in  the  usual  way,  diazotizing 
in  a  cold  bath  of  sodium  nitrite  acidulated  with  hydrochloric  acid, 
and  "developing"  in  a  suitable  developer  to  produce  the  desired 
color. 

Wool  is  dyed  from  baths  containing  salt  or  Glauber's  salt,  with 
the  addition  of  a  little  acetic  acid  to  render  the  color  fast  to  milling. 
The  shades  are  generally  faster  and  deeper  than  on  cotton. 

Mixed  wool  and  cotton  goods  ("  unions  ")  are  often  colored  with 
such  direct  dyes  as  have  equal  affinity  for  the  two  fibres,  in  order 
that  the  shades  may  match.  The  evenness  of  the  shade  in  these 
goods  can  often  be  improved  by  varying  the  amount  of  assistant 
employed  in  the  bath. 

Silk  takes  the  direct  dyes  very  well,  fast  and  brilliant  shades 
being  obtained.  The  assistant  used  is  sodium  phosphate  or  soap. 
Mixed  silk  and  cotton  goods  are  also  dyed  with  these  colors ;  since 
some  of  them  color  cotton  but  not  silk  in  a  soap  bath,  it  is  often 
possible  to  dye  two  shades  on  such  mixed  goods,  producing  varieties 
of  "  changeable  "  or  u  shot "  effects.  For  example,  the  cotton  may 
be  dyed  in  a  soap  bath  and  the  silk  dyed  in  a  second  bath  of  an 
azo  or  acid  color,  which  has  no  affinity  for  cotton. 

2.  Basic  dyes  are  the  salts  of  colorless  bases  which  contain 
chromophorous  groups.  The  color  does  not  appear  until  the  forma- 
tion of  the  salt.  The  dyestuffs  decompose  in  the  dye-bath,  setting 
free  the  acid,  while  the  base  combines  with  an  acid  constituent  of 
the  animal  fibre,  or  with  the  acid  mordant  in  the  case  of  vegetable 
fibre.  These  dyes  are  monogenetic,  but  they  varyt  much  in  their 
constitution,  fastness,  and  brilliancy  of  shade.  They  have  great 
tinctorial  power,  but  are  generally  fugitive,  being  rapidly  faded  by 
light,  soap,  and  milling.  The  commercial  dyestuffs  are  usually  salts 
of  acetic,  oxalic,  nitric,  sulphuric,  or  hydrochloric  acid,  and  most  of 
them  are  soluble  in  water.  They  are  used  in  neutral  or  slightly 


484  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

alkaline  or  acid  baths.  Excess  of  acid  or  alkali  must  be  avoided, 
as  it  prevents  complete  exhaustion  of  the  dye-bath.  Calcareous 
water  is  especially  bad  for  these  colors,  since  it  precipitates  the 
color  bases  as  a  white,  curdy  mass  which  adheres  to  the  fibre, 
weakening  the  color  and  causing  spots  and  uneyenness.  Basic  dyes 
can  be  mixed  in  the  same  bath  to  form  compound  shades. 

Cotton  is  generally  mordanted  with  tannin,  Turkey-red  oil,  or 
soap,  before  dyeing  with  basic  dyes.  The  mordanted  cotton  is  dyed 
in  a  separate  bath,  to  which  the  color  is  added  in  small  portions  at 
a  time  during  the  dyeing,  to  prevent  unevenness  in  the  shade.  The 
temperature  is  raised  slowly  to  60°  C.,  but  no  higher,  lest  the  brill- 
iancy be  injured.  The  goods  are  wrung,  or  hydro-extracted,  but  not 
washed,  after  dyeing. 

Wool  is  dyed  directly  by  the  basic  dyes,  but  a  little  acetic,  sul- 
phuric, or  hydrochloric  acid,  or  alum  or  sodium  acid  phosphate  is 
added,  to  moderate  the  absorption  and  afford  level  dyeing.  The  wool 
fibre  has  an  acid  character,  decomposing  the  dye,  and  combining  with 
the  color  base  to  form  a  lake.  But  certain  basic  dyes,  especially 
methyl  and  benzaldehyde  greens,  will  not  dye  wool  until  it  has  been 
mordanted  with  sulphur  by  treating  with  sodium  thiosulphate,  alum, 
and  sulphuric  acid.  The  mordant  is  then  fixed  in  very  dilute 
ammonia.  The  dyeing  is  usually  done  in  a  boiling  bath,  the  tem- 
perature being  afterwards  lowered  to  60°  C.,  or  even  to  40  °C., 
while  the  wool  remains  in  the  bath. 

Silk  has  greater  affinity  for  basic  dyes  than  has  wool.  The  dye- 
ing is  done  in  a  neutral,  alkaline,  or  slightly  acid  bath  ;  usually  an 
alkaline  bath  with  soap  or  "boiled-off  liquor"  is  employed.  The 
temperature  is  between  80°  C.  and  boiling.  For  the  acid  bath,  acetic, 
tartaric,  or  sulphuric  acid  is  generally  used.  After  dyeing  and 
washing  the  silk  is  generally  "  brightened  "  by  passing  through  a 
dilute  acid,  and  after  hydro-extracting,  is  dried. 

Union  goods  are  dyed  in  a  neutral  or  acid  bath,  the  cotton  having 
been  previously  mordanted  cold,  with  tannin  and  antimony,  which  do 
not  unite  with  wool.  Silk  and  cotton  mixed  goods  are  first  dyed  so 
that  the  silk  is  colored,  and  are  then  passed  through  cold  tannic  acid 
to  mordant  the  cotton,  and  dyed  a  second  time. 

3.  Acid  dyes  are  dyed  in  acid  baths,  and  may  be  mixed  in  the 
same  bath  for  compound  shades.  But  some  of  them  act  like  direct 
dyes  when  used  on  cotton,  while  others  are  dyed  on  mordanted  wool. 
The  classification  is  somewhat  arbitrary,  but  an  acid  bath  is  always 
used  for  animal  fibres.  The  commercial  dyestuffs  consist  of  the 
alkali  or  lime  salts  of  the  color  acid,  excepting  only  picric  acid, 


TEXTILE  INDUSTRIES  485 

which  is  used  in  the  free  state,  its  salts  being  explosive.  The  acid 
dyes  are  grouped,  according  to  their  constitution,  into :  — 

(1)  Nitro  compounds. 

(2)  Sulphonated  basic  dyes. 

(3)  Azo  colors. 

Sometimes  the  eosins  are  classed  with  the  acid  dyes,  since  they  are 
also  dyed  from  a  very  weak  acid  (dilute  acetic)  bath. 

The  nitro  dyes  owe  their  acid  nature  and  coloring  properties  to 
the  chromophorous  nitro  groups  which  they  contain.  Besides  these, 
there  are  usually  auxochromous  radicals,  such  as  hydroxyl  or  the 
imido  group  (NH)  present.  The  sulphonated  basic  dyes  are  derived 
from  bases  which  are  coloring  matters,  by  introducing  the  sulpho 
group  (SO;{H).  This  group  causes  no  material  change  in  the  shade 
of  the  basic  dye,  but  the  coloring  power  is  reduced,  and  the  dye  can 
no  longer  combine  with  tannin  mordants;  the  fastness  to  light  is 
much  increased.  The  azo  colors  contain  the  azo  group  (—  N  =  N  — ) 
as  chromophor,  and  as  auxochromous  group,  either  hydroxyl  or 
amido  groups,  NH2.  These  are  the  most  numerous  and  important  of 
the  acid  dyes,  and  are  most  extensively  used  on  wool.  Some  of  the 
azo  colors  may  be  dyed  without  a  mordant,  while  others  are  dyed 
upon  a  metallic  mordant,  such  as  alum,  chromium  fluoride,  or  potas- 
sium bichromate.  The  colors  are  fast  upon  wool,  and  fairly  so  on 
silk,  and  are  chiefly  used  for  these  fibres.  They  are  fast  to  light 
and  acids,  but  since  they  are  not  fast  to  washing,  their  use  on  vege- 
table fibres  is  limited. 

Cotton  is  dyed  in  a  very  concentrated  bath,  to  which  common 
salt,  alum,  and  acetic  acid  are  added;  or  a  mordant  bath  of  alum  and 
soda  (basic  alum),  or  of  stannic  chloride,  followed  by  basic  alum,  is 
used  before  dyeing.  Tannin  treatment  before  the  alum  mordanting 
renders  the  color  faster  to  washing.  (The  shades  on  unmordanted 
cotton  are  not  fast  to  washing.)  After  mordanting,  the  goods  are 
wrung  and  dyed  without  washing.  After  dyeing,  they  are  dried 
without  washing.  Mordanted  cotton  is  dyed  at  about  50°  C. ;  but 
for  unmordanted  goods  the  temperature  is  slowly  raised  to  boiling. 
Linen  is  rarely  dyed  with  acid  colors,  since  the  shades  are  not  fast 
enough  to  warrant  it. 

Wool  is  dyed  with  acid  colors  in  a  boiling  bath  of  the  dyestuff, 
to  which  a  restraining  assistant  (Glauber's  salt)  may  or  may  not  be 
added.  To  develop  the  color,  sulphuric  acid  is  added,  a  little  at  a 
time,  during  the  boiling,  thus  freeing  the  color-acid  very  gradually, 
and  affording  level  shades.  Sometimes  ammonium  acetate,  or  sul- 
phate, is  used  in  the  dye-bath,  which,  decomposing  slowly  in  the 


486  OUTLINES   OF   INDUSTRIAL   CHEMISTRY 

boiling  liquor,  sets  free  its  acid,  while  ammonia  escapes.  The  free 
acid  then  decomposes  the  dyestuff,  and  the  color-acid  is  deposited  on 
the  fibre.  In  the  case  of  the  alkali  blues,  the  color-acid  is  insoluble 
in  water,  but  its  alkali  salt  dissolves  readily,  yielding  colorless  solu- 
tions. To  dye  these,  the  goods  are  boiled  in  a  bath  of  borax  or  soda, 
to  which  the  dyestuff  is  added;  when  impregnated  with  the  alkaline 
solution,  the  wool,  still  uncolored,  is  dipped  in  an  acid  bath.  This 
decomposes  the  alkali  salt,  and  the  free  color-acid  develops  on  the 
fibre  as  a  deep  blue  color.  The  acid  colors,  especially  the  sul- 
phonated  basic  dyes,  when  dyed  on  the  fibre,  are  destroyed  by  alka- 
lies. Some  are  very  fugitive  to  light. 

Silk  is  usually  dyed  in  a  slightly  acid  bath  containing  10  per 
cent  "boiled-off  liquor."  The  dye  solution  is  sometimes  added  to 
'the  bath  all  at  once;  in  other  cases  it  is  added  gradually,  the  tem- 
perature being  kept  near  boiling.  After  dyeing,  silk  is  washed  and 
passed  into  a  dilute  acid  solution  to  brighten  the  color,  and  is  dried 
without  further  washing. 

4.  The  mordant  dyes  yield  colors  which  are  generally  fast  to 
washing,  soaping,  milling,  and  light.  They  comprise  a  great  variety 
of  coloring  matters,  both  of  natural  and  artificial  origin,  which  are 
dyed  on  all  fibres  by  the  aid  of  metallic  mordants.  Many  of  these 
dyes  are  polygenetic,  and  they  all  possess  the  property  of  forming 
insoluble  color  lakes  with  metallic  oxides.  The  mordanted  goods  are 
passed  into  a  dye-bath,  which  usually  contains  nothing  but  the  color ; 
but  in  the  case  of  certain  natural  dyewoods,  the  mordant  and  dye 
may  be  applied  in  the  same  bath,  while  in  others  the  goods  are  first 
impregnated  with  the  dye,  and  the  color  fixed  on  the  fibre  by 
subsequent  treatment  in  the  mordant  bath.  This  last  process  is 
generally  known  as  "  stuffing  and  saddening." 

The  mordant  oxides  chiefly  employed  are  those  of  aluminum, 
chromium,  iron,  and  tin.  Mordant  colors  may  be  mixed  in  the  same 
dye-bath,  provided  the  same  mordant  is  used  for  each.  Many  of  the 
artificial  mordant  colors  are  nearly  insoluble  in  water,  and  if  once 
dried,  are  difficult  to  again  dissolve  in  the  dye-bath.  Hence  they 
are  often  sold  as  "pastes,"  containing  from  60  to  80  per  cent  of 
water.  The  mordant  colors  themselves  frequently  serve  as  mordants 
for  fixing  basic  dyes,  hence  the  latter  are  often  used  to  brighten  the 
shade  of  the  former. 

Cotton  is  always  mordanted  in  separate  baths  before  dyeing  with 
these  colors.  Until  recently,  mordanting  with  chromium  on  cotton 
has  been  difficult,  and  the  results  of  the  dyeing  unsatisfactory, 
especially  on  yarn.  But  the  application  of  certain  basic  chromium 


TEXTILE   INDUSTRIES  487 

acetates,  chlorides,  etc.,  especially  by  Koechlin's  method  (p.  458), 
has  made  it  possible  to  dye  new  shades  on  cotton.  Sometimes  the 
cotton  is  prepared  with  Turkey-red  oil  before  mordanting  with 
chromium.  Aluminum  mordants  are  largely  used  on  cotton  for  mor- 
dant colors,  but  iron  and  tin  less  frequently.  Turkey-reds,  alizarin 
red,  ccerulei'n,  and  other  alizarin  colors,  and  logwood  blacks,  are  the 
chief  mordant  colors  on  cotton.  For  centuries  Turkey-reds  have 
been  produced  on  cotton  by  the  aid  of  madder,  oil,  and  aluminum  salts, 
This  gives  a  most  brilliant  red,  and  one  of  the  fastest  colors  to  light, 
washing,  or  friction,  as  well  as  to  chemical  reagents.  By  the  old 
process,  much  time,  usually  about  four  weeks,  was  consumed  in  the 
dyeing,  but  now  it  has  been  shortened  to  about  three  days.  Madder 
has  been  completely  replaced  by  the  artificial  alizarin,  produced  from 
coal-tar  (anthracene,  p.  284).  The  process  of  dyeing  Turkey-reds 
on  cotton  is  complicated,  and  a  special  mordanting  of  the  goods  is 
necessary.  The  outline  of  the  process  is  as  follows :  The  bleached 
cotton  (p.  451)  is  first  oiled  with  olive,  castor,  or  Turkey-red  oil, 
(p.  312)  the  goods  being  steeped  in  an  emulsion  of  the  oil  in  sodium 
carbonate  solution,  or  padded  in  a  10  or  15  per  cent  solution  of 
neutralized  Turkey-red  oil  in  water.  The  excess  of  oil  is  squeezed 
out  and  the  goods  "  aged,"  or  steamed,  at  about  5  pounds  pressure, 
to  render  the  oil  insoluble  and  to  fix  it  on  the  fibre.  An  oxidation 
and  probable  polymerization  of  the  oleic  acid  and  other  constituents 
of  the  oil  occurs,  and  substances  are  fixed  in  the  fibre  which  combine 
with  and  assist  in  the  fixing  of  the  metallic  mordants,  and  also,  per- 
haps, form  a  varnish  coat  over  the  color  lake,  protecting  it  from  air 
and  chemicals,  thus  increasing  the  fastness  and  lustre  of  the  dyed 
fabric.  The  oiled  cotton  is  then  sometimes  steeped  in  a  decoction 
of  sumach,  but  this  is  not  essential,  and  is  very  generally  omitted. 
The  mordanting  is  done  by  working  the  goods  in  a  tepid  solution  of 
aluminum  acetate  (red  liquor),  or  basic  aluminum  sulphate,  the  oxide 
being  fixed  by  aging,  or  by  treatment  in  a  bath  of  powdered  chalk 
and  water,  or  sodium  phosphate,  which  also  removes  the  excess  of 
oil  from  the  fibre.  Formerly  sodium  arsenate  was  used  for  this 
"  dung-bath,"  and  afforded  very  light  shades.  The  dyeing  is  accom- 
plished by  entering  the  mordanted  cotton  in  a  cold  bath  of  alizarin 
suspended  in  water,  containing  some  lime,  calcium  being  essential 
to  the  formation  of  the  colored  lake ;  hard  water,  free  from  iron,  is 
preferred  for  this  bath,  but  if  not  available,  powdered  chalk  or 
calcium  acetate  is  added.  The  temperature  is  very  slowly  raised  to 
70°  C.,  where  it  is  kept  until  the  dye-bath  is  exhausted.  The  cotton 
is  then  wrung  and  dried.  The  color  at  this  time  is  a  dull  red,  and, 


488  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

to  develop  the  brilliant  shade,  the  goods  are  steamed  at  about  15 
pounds  pressure  for  an  hour.  Sometimes  they  are  oiled  a  second 
time  before  steaming.  They  are  then  thoroughly  washed  with  soap, 
two  or  three  soapings  being  usually  given.  Stannous  chloride  is 
sometimes  added  to  the  soap  bath  to  increase  the  brilliancy ;  also  it 
is  very  essential  in  Turkey-red  dyeing  that  neither  the  mordants  nor 
the  dye-bath  shall  be  contaminated  with  the  slightest  trace  of  iron  in 
any  form. 

Turkey-reds  are  dyed  by  several  other  processes,  which  cannot 
be  considered  here.* 

Various  shades  of  violet,  lilac,  and  purple  are  dyed  on  cotton 
with  alizarin  by  mordanting  with  ferrous  acetate  (pyrolignite  of 
iron,  p.  263)  instead  of  red  liquor,  and  usually  omitting  the  oiling. 
A  tannin-iron  mordant  affords  purple  blacks,  while  mixtures  of  iron 
and  aluminum  mordants  give  various  shades  from  claret  red  to 
chocolate. 

Linen  is  dyed  with  alizarin  in  the  same  way  as  cotton.  The 
fastness  of  Turkey-red  to  washing  and  soap  makes  it  especially 
valuable  for  dyeing  linen  yarn,  which  is  then  woven  into  figured 
wash  goods.  Other  alizarin  colors  are  dyed  on  cotton  and  linen 
with  the  various  aluminum,  chromium,  and  iron  mordants.  The 
methods  vary  somewhat  with  each  dye,  and  must  be  sought  for  in 
special  works  on  dyeing. 

Logwood  yields  blacks  and  grays  on  cotton  mordanted  with  tan- 
nin and  iron,  or  with  iron  salts  alone.  "Nitrate"  and  acetate  of 
iron  give  the  best  shades,  but  copperas  is  much  used  for  cheap 
blacks.  Stannous  chloride  yields  purple  shades,  while  blues  are 
obtained  with  copper  sulphate  or  acetate. 

Wool  is  largely  dyed  with  mordant  colors,  both  natural,  such  as 
logwood,  fustic,  quercitron,  and  cochineal,  and  with  artificial  aliza- 
rins and  azo  colors.  The  alizarin  colors  are  generally  faster  to 
light,  chemicals,  milling,  and  washing  than  the  natural  coloring 
matters.  It  is  very  essential  in  dyeing  wool  with  the  mordant 
colors  that  the  fibre  shall  be  thoroughly  scoured,  and  entirely  free 
from  oil  or  grease,  as  these  would  form  soaps  with  the  metallic  mor- 
dants, and  cause  spots  on  the  goods  while  making  the  color  less  fast 
to  milling  and  friction.  The  mordants  for  wool  are  generally  the 
same  as  those  for  cotton;  aluminum  salts  are  employed  for  aliza- 
rin, but  chromium  is  the  usual  mordant  for  these  dyes.  The  wool 
is  boiled  with  about  3  per  cent  (of  the  weight  of  the  goods)  of  potas- 
sium bichromate,  often  with  the  addition  of  1  per  cent  sulphuric 
*  See  Dyeing  of  Textile  Fabrics,  J.  J.  Hummel,  p.  427  et  seq. 


TEXTILE  INDUSTRIES  489 

acid.  Cream  of  tartar  is  sometimes  used  with  bichromate  for  the 
finest  work.  About  3  per  cent  of  chromium  fluoride,  with  half  its 
weight  of  oxalic  acid,  has  been  much  used  of  late  years.  After  the 
oxide  is  fixed  by  aging  several  hours  in  a  dark  place,  the  wool  is 
washed,  and  is  ready  for  dyeing.  The  dye-bath  is  generally  pre- 
pared with  pure  water  and  the  dye  alone,  but  for  some  of  the  aliza- 
rin colors  a  very  little  acetic  acid  is  added.  The  goods  are  entered 
when  the  bath  is  about  30°  to  40°  C.,  and  the  temperature  is  raised 
slowly  so  that  it  reaches  the  boiling  point  in  an  hour;  the  boiling 
is  continued  for  another  hour  or  more.  If  these  precautions  are  not 
observed,  the  dyeing  is  apt  to  be  uneven. 

Some  of  the  alizarin  colors  may  be  mordanted  and  dyed  in  one 
bath ;  potassium  bichromate  or  chromium  fluoride  are  used  in  this  way, 
the  goods  being  entered  into  the  cold  bath,  which  is  slowly  raised  to 
boiling.  The  dyes  must  be  able  to  withstand  the  oxidizing  action  of 
chromic  acid.  This  "  single  bath  "  process  is  very  apt  to  waste  color, 
and  the  shades  produced  are  less  fast,  especially  to  milling. 

Silk  is  not  commonly  dyed  with  mordant  colors,  since  the  shades 
are  less  brilliant  than  those  obtained  with  the  substantive  dyes,  and 
the  latter  are  cheaper  and  sufficiently  fast  for  most  purposes  on  silk. 
When  mordant  dyes  are  used,  the  silk  is  first  mordanted  by  steeping 
in  basic  aluminum  sulphate  or  acetate  for  some  hours,  and  fixing  in 
cold  silicate  of  soda  solution  at  J°  Tw.  It  is  then  dyed  without  dry- 
ing. For  chrome  mordanting,  a  solution  of  chromium  chloride  is 
used.  The  dye-bath  is  prepared  with  "  boiled-off  liquor,"  which  is 
neutralized  or  slightly  acidified  with  acetic  acid.  The  silk  is  worked 
in  the  cold  bath  for  15  minutes,  and  then  the  temperature  is  slowly 
raised  to  boiling,  and  kept  there  for  an  hour.  After  washing  in 
water,  the  silk  is  passed  into  boiling  soap  liquor,  and  finally  bright- 
ened by  very  dilute  acetic  acid  at  30°  to  40°  C. 

'  5.  The  special  dyes  include  those  colors  which  are  prepared  or 
developed  directly  on  the  fibre  by  peculiar  processes.  They  include 
indigo,  aniline  black,  certain  azo  colors  developed  on  the  fibre,  and 
the  mineral  colors  used  in  dyeing.  Indigo,  p.  466,  is  chiefly  dyed  on 
cotton  and  wool.  It  is  insoluble  in  water,  but  by  reducing  agents  is 
converted  into  indigo  white,  which  is  soluble  in  alkaline  liquors. 
This  reduction  is  performed  in  the  vat  in  which  the  dyeing  is  to  be 
done.  Cotton  is  dyed  with  indigo  in  the  "  hyposulphite,"  or  "  hydro- 
sulphite  "  vat,  the  copperas  vat,  or  the  zinc  vat.  The  hydrosul- 
phite  vat  is  prepared  by  reducing  indigo  with  sodium  hyposulphite, 
NaHS02,  p.  44.  The  indigo  is  mixed  with  milk  of  lime,  and  the 
hyposulphite  liquor  added  and  heated  to  CO0  C.,  until  the  liquor 


490  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

becomes  yellow.  After  cooling,  the  bronze  colored  scum  is  removed, 
and  the  cotton  is  at  once  immersed  in  the  reduced  indigo  solution. 
When  the  fibre  is  impregnated  with  the  liquor,  it  is  passed  through 
squeeze-rolls,  and  exposed  to  the  air  until  the  indigo  white  becomes 
oxidized,  forming  indigo  blue,  the  color  being  developed  in  the  inte- 
rior of  the  fibre.  The  copperas  vat  is  made  by  adding  indigo  to  a 
copperas  solution,  and  then  slowly  running  in  milk  of  lime.  The 
reactions  occuring  are  probably  as  follows  :  — 

1)  FeS04  +  Ca(OH)2  =  Fe(OH)2  +  CaS04. 

2)  2  Fe(OH)2  +  2  H2O  =  2  Fe(OH)3  +  H2. 

3)  deHjoN  A  +  H2  =  CuHuN  A- 


The  hydrogen  is  not  set  free  as  gas,  but  immediately  combines  with 
the  indigo  to  form  indigo  white,  which  is  dissolved  by  the  excess 
milk  of  lime.  The  copperas  must  be  free  from  copper,  or  ferric  and 
aluminum  sulphates  to  prevent  loss,  and  the  indigo  must  be  ground 
very  fine.  (The  sediment  is  quite  bulky  in  this  vat.)  The  cotton  is 
treated  the  same  as  in  the  hydrosulphite  vat. 

The  zinc  vat  is  prepared  by  adding  zinc  dust  to  a  mixture  of 
indigo  and  milk  of  lime.  The  zinc  decomposes  water  in  the  presence 
of  lime,  and  forms  zinc  oxide,  while  the  hydrogen  reduces  the  indigo 
to  indigo  white,  which  dissolves.  The  amount  of  sludge  formed  in 
this  vat  is  small,  and  the  process  is  easily  managed.  By  feeding  the 
vat  with  more  indigo,  lime,  or  zinc,  as  required,  it  can  be  kept  in 
good  order  for  months.  Excess  of  zinc  causes  frothing.  The  dye- 
ing process  is  similar  to  those  above  described. 

Loose  wool  or  yarn  is  dyed  with  indigo  in  the  hydrosulphite 
vat,  prepared  as  for  cotton.  The  woad  vat  is  used  for  woollen  cloth  ; 
a  mixture  of  woad  with  water  is  allowed  to  stand  for  some  hours  at 
70°  C.,  and  then  bran,  indigo,  madder,  and  lime  are  added.  A  butyric 
fermentation  sets  in,  and  when  this  is  well  established  more  lime 
is  added;  hydrogen  is  set  free,  and  reduces  the  indigo.  In  about 
three  days  the  vat  is  ready  for  dyeing.  After  use,  more  lime  and 
bran  are  added  as  required  to  control  the  fermentation,  and  every 
day  or  two  more  indigo  is  put  into  the  vat.  The  wool,  wet  in  warm 
water,  and  wrung,  is  submerged  in  the  vat,  where  it  is  worked  from 
twenty  minutes  to  two  hours.  It  is  then  wrung  to  recover  as  much 
of  the  indigo  solution  as  possible,  and  at  once  exposed  to  the  air  to 
oxidize  the  indigo  white.  For  clear,  fast  blues,  the  goods  are  returned 
to  the  vat  two  or  three  times.  For  the  best  and  fastest  color,  the 
wool  should  be  dyed  before  weaving,  and  sometimes  dyed  again 
after  milling.  After  dyeing,  the  goods  are  very  thoroughly  washed 


TEXTILE  INDUSTRIES  491 

with  water  in  a  "dolly,"  and  then  scoured  with  soap  and  fuller's 
earth  to  remove  all  the  loosely  adhering  indigo,  which  would  other- 
wise cause  the  goods  to  "  crock." 

It  is  often  customary  to  dye  woollens  with  red  woods  before 
the  indigo  dyeing,  in  order  to  give  "bloom"  to  the  finished 
goods. 

The  soda  vat  is  used  quite  extensively  in  Europe.  In  this, 
molasses,  bran,  lime,  and  sodium  carbonate  are  mixed  with  indigo ; 
a  butyric  fermentation  results,  and  the  indigo  is  reduced.  The  colors 
obtained  are  brighter  than  in  the  woad  vat,  but  not  so  full. 

Indigo  was  formerly  reduced  in  a  vat  containing  putrid  urine, 
salt,  and  madder.  The  ammonium  carbonate  formed  by  the  putre- 
faction dissolves  the  reduced  indigo.  The  process  has  been  generally 
given  up. 

Silk  is  not  dyed  with  indigo  to  any  extent. 

Aniline  black  is  a  dye  of  unknown  constitution,  produced  on  the 
fibre  by  oxidation  of  aniline.  It  is  insoluble  in  all  solvents  except 
strong  sulphuric  acid.  It  is  extensively  produced  on  cotton,  but  is 
not  suitable  for  animal  fibres,  since  it  injures  the  strength,  lustre,  and 
feel  of  the  goods.  Unless  great  care  is  exercised,  even  cotton  fibre 
is  weakened.  The  oxidizing  agent  generally  employed  in  coloring 
yarn  is  potassium  bichromate  in  acid  solution,  but  for  piece  goods 
sodium  or  potassium  chlorate  is  preferred.  The  direct  oxidation  of 
aniline  is  difficult,  unless  certain  easily  decomposed  metallic  salts 
are  present  to  act  as  carriers  of  oxygen.  Of  these,  cupric  chloride, 
sulphate,  or  sulphide,  or  cuprous  sulphocyanide  are  generally  used ; 
vanadium  chloride  in  minute  quantities  produces  a  rapid  and  suc- 
cessful oxidation  of  the  aniline.  Potassium  ferrocyanide  is  also  ef- 
fective. For  calico  printing,  the  soluble  copper  salts  are  not  used, 
since  they  injure  the  printing  rolls  and  "doctors  "  of  the  machine. 
To  produce  level  dyeing  and  for  the  most  complete  utilization  of  the 
materials  of  the  bath,  the  process  is  carried  on  at  a  moderate  tem- 
perature (50°  to  60°  C.)  in  many  cases.  But  such  blacks  are  usually 
incompletely  oxidized  and  are  very  apt  to  develop  a  green  shade 
after  a  time,  or  if  exposed  to  the  action  of  acids.  This  greening  may 
be  prevented  by  dyeing  at  a  temperature  of  75°  C.,  but  in  this  case 
the  reactions  between  the  constituents  of  the  bath  take  place  very 
rapidly,  and  the  color  is  loosely  deposited  upon  and  not  within  the 
fibre,  and  the  goods  "  crock  "  badly ;  at  the  same  time,  much  black 
is  precipitated  in  the  dye-bath  and  thus  lost. 

Many  different   receipts   for   dyeing  aniline  blacks   have  been 


492  OUTLINES  OF  INDUSTRIAL   CHEMISTRY 

devised,  but  the  following,  proposed  by  Evans*  will  furnish  an 
example :  — 

10  parts  ammonium  chloride. 

10  parts  sodium  chlorate. 

10  parts  copper  sulphate. 

35  parts  aniline  hydrochloride  (crystals). 

X  parts  aniline  oil. 
200  parts  water. 

The  ammonium  chloride  and  sodium  chlorate  are  dissolved  together 
in  65  parts  water;  the  copper  sulphate  is  dissolved  in  55  parts 
water ;  the  aniline  hydrochloride  is  dissolved  in  a  little  hot  water 
and  neutralized  with  sufficient  (X  parts)  aniline  oil.  All  solutions 
are  thoroughly  cooled  and  then  the  aniline  hydrochloride  is  added 
to  the  sodium  chlorate ;  next  the  copper  solution  is  stirred  in  and 
water  sufficient  to  make  the  density  of  the  mixture  14°  Tw.,  is  added. 
The  cotton  is  padded  two  or  three  times  in  this  liquor  and  all  excess 
is  removed  in  a  centrifugal  machine.  The  goods  are  then  "  aged  " 
by  exposure  for  14  hours  in  an  atmosphere  near  30°  C.  They  are 
then  treated  at  80°  C.  in  a  bath  of  potassium  bichromate  (10  parts), 
soda  (5  parts),  common  salt  (5  parts),  and  water  (1000  parts).  They 
are  then  washed  in  slightly  warm  water  and  steamed  at  15  pounds 
to  develop  the  color  fully. 

Aniline  blacks  are  often  "  topped  "  with  methyl  violet  or  logwood 
to  prevent  "  greening  "  and  crocking. 

Cotton  and  linen  are  now  often  dyed  with  insoluble  azo  dyes,  de- 
veloped on  the  fibre.  These  are  fast  to  acids,  alkalies,  and  washing, 
but  fade  in  the  light  and  will  often  "  crock."  They  are  produced  by 
impregnating  the  fibre  with  a  phenol  (naphthol)  and  developing  the 
color  by  treating  the  saturated  fibre  in  a  cold  bath  of  the-diazotized 
base.  After  washing  in  water,  the  goods  are  soaped  at  60°  C.  and 
again  washed  to  make  the  color  as  fast  as  possible  to  rubbing.  The 
diazo  compound  is  prepared  by  treating  an  amido  body  with  sodium 
nitrite  and  hydrochloric  acid  at  a  low  temperature.  The  amido 
bodies  used  are  such  substances  as  para-nitraniline,  yielding  a  scar- 
let, methyl-amido-phenol  (anisidine),  yielding  a  blue,  and  some 
others. 

Certain  so-called  mineral  dyes  are  produced  on  the  fibre  by  satu- 
rating it  with  a  solution  of  metallic  salt,  and  passing  it  into  a  second 
solution  which  decomposes  the  first  salt,  forming  a  colored  precipi- 
*  J.  Soc.  Dyers  and  Colorists,  1891,  p.  20. 


TEXTILE   INDUSTRIES  493 

tate  on  the  fibre.  The  most  important  mineral  colors  are  chrome 
yellow  and  orange,  iron  buff,  Prussian  blue,  and  manganese  brown. 

Chrome  yellow  is  dyed  on  cotton  as  follows :  The  fibre  is  soaked 
in  a  solution  of  lime-water ;  after  wringing,  it  is  soaked  in  a  solution 
of  lead  acetate  or  nitrate,  a  basic  salt  being  preferable  since  it  de- 
posits a  larger  amount  of  lead  on  the  fibre.  The  cotton  is  then  re- 
turned to  the  lime-water  bath,  and,  after  wringing,  is  passed  into  a 
solution  of  sodium  or  potassium  bichromate,  to  develop  the  color. 
After  passing  through  a  bath  of  very  dilute  hydrochloric  acid,  the 
cotton  is  washed  and  dried.  By  adding  zinc  sulphate  to  the  chrome 
bath,  the  shade  of  yellow  may  be  lightened. 

Chrome  orange  is  produced  by  treating  the  fibre  in  a  bath  of  lime- 
water  or  alkali,  after  dyeing  with  chrome  yellow ;  this  produces  basic 
lead  chromate  (p.  206). 

Chrome  green  is  not  important  since  it  is  very  pale  and  of  no  par- 
ticular beauty.  It  is  produced  on  cotton  by  the  processes  used  for 
mordanting  with  chromium  salts  (p.  458).  On  wool  it  may  be  formed 
by  digesting  the  fibre  in  a  strong  solution  of  bichromate,  and  then 
passing  it  through  a  sodium  bisulphite  solution. 

Iron  buff,  or  nankin  yellow,  consists  of  ferric  hydroxide,  precipi- 
tated on  the  fibre.  It  is  only  dyed  on  cotton,  the  fibre  being  satu- 
rated with  a  solution  of  iron  salt  and  the  color  developed  by 
treatment  with  caustic  soda,  soda-ash,  or  calcium  hydroxide  solution, 
in  the  same  way  as  when  mordanting  with  iron  salts  (p.  460).  By 
repeating  the  operation,  greater  depth  of  color  may  be  obtained. 
When  ferrous  salts  are  used,  they  are  oxidized  by  treating  the  fibre 
in  a  bath  of  bleaching  powder  solution,  after  precipitating  the  hy- 
droxide. The  iron  salts  generally  used  are  the  basic  ferric  sulphate 
(nitrate  of  iron)  and  ferric  nitrate.  Pyrolignite  of  iron  is  unsuitable 
because  the  tarry  impurities  prevent  the  development  of  pure  shades. 

Prussian  blue  is  produced  on  the  fibre  by  two  methods.  For 
cotton  it  is  customary  to  first  dye  an  iron  buff  and  then  digest  it  in 
a  solution  of  potassium  ferrocyanide,  acidulated  with  hydrochloric 
acid.  Deeper  shades  are  produced  by  repeating  the  process  for  buff, 
and  again  developing  the  blue. 

Wool  is  sometimes  dyed  with  Prussian  blue  but  without  previous 
mordanting  with  iron.  The  wool  is  introduced  into  the  cold  bath  of 
potassium  ferrocyanide,  strongly  acidulated  with  sulphuric  or  nitric 
acid.  The  temperature  is  slowly  raised  to  boiling,  whereby  the  yellow 
prussiate  is  decomposed  and  the  blue  pigment  deposited  in  the  fibre. 
The  color  is  brightened  by  the  addition  of  a  little  stannous  chloride 
or  "  muriate  of  tin  "  to  the  bath  during  the  last  half -hour  of  boiling. 


494  OUTLINES   OF  INDUSTRIAL   CHEMISTRY 

Silk  is  dyed  with  Prussian  blue  in  the  process  of  weighting 
(p.  460)  for  black  dyeing,  the  mordant  in  this  case  being  basic  ferric 
sulphate.  If  the  blue  color  is  to  remain  as  the  final  dye,  the  goods 
are  softened  after  dyeing,  by  working  in  a  bath  containing  a  little 
olive  oil  and  sulphuric  acid. 

Manganese  brown  consists  of  the  hydroxide,  or  oxide,  of  man- 
ganese, and  is  only  dyed  on  cotton.  The  goods  are  steeped  in 
manganous  chloride  solution,  free  from  acid,  and  the  color  is  de- 
veloped in  a  mixed  solution  of  caustic  soda  and  bleaching  powder. 
Or  a  deep  brown  is  developed  by  passing  the  goods  through  a  bath 
containing  potassium  permanganate  and  sodium  carbonate  solutions. 

This  color  is  fast  to  light,  soap,  and  dilute  acids  and  alkalies, 
and  may  also  serve  as  a  base  on  which  to  dye  aniline  blacks ;  in 
this  case  the  oxide  on  the  fibre  assists  in  the  oxidation  of  the 
aniline. 

TEXTILE   FEINTING 

Textile  printing  may  involve  the  application  of  a  single  coloring 
matter  to  one  side  of  the  fabric,  or  the  forming  of  intricate  designs 
in  as  many  as  18  or  20  different  colors,  by  one  passage  of  the  cloth 
through  the  printing  machine.  The  pattern  is  usually  produced  on 
one  side  only  of  the  cloth,  but  sometimes  the  same  or  a  different 
design  appears  on  each  side.  There  may  be  a  colored  figure  on  a 
white  or  colored  background,  or  a  colorless  design  may  be  produced 
on  a  colored  background.  Textile  printing  is  sometimes  called 
topical  coloring. 

The  earliest  attempts  at  this  form  of  decoration,  made  by  pre- 
historic races,  were  doubtless  carried  out  by  mixing  pigments  with 
water  or  with  a  gum  solution,  and  painting  the  design  on  the  fabric. 
Later,  the  art  was  developed  to  painting  the  mordants  in  the  form 
of  the  design,  and  then  dyeing  the  fabric  in  some  natural  dyestuffs. 
Stencilling  was  also  invented  early,  but  the  first  great  advances  were 
made  with  the  invention  of  block  printing,  which  was  followed  by 
roller  printing. 

For  block  printing  the  design  is  made  in  relief  on  blocks  of  hard 
wood.  The  cloth  is  spread  evenly  on  a  firm  table,  and  the  printer, 
having  daubed  the  relief  with  color,  applies  the  block  to  the  cloth 
and  strikes  it  with  a  hammer  to  drive  the  color  into  the  fabric.  In 
order  that  the  lines  of  the  figure  may  not  overlap,  or  spaces  be  left 
imprinted  which  should  be  colored,  exact  placing  or  "  registering " 
of  the  block  is  very  important.  This  is  gauged  by  pin  points  set 
in  the  corners  of  the  block,  which  mark  the  exact  spot  where  it  is 


TEXTILE   INDUSTRIES  495 

to  be  applied  for  the  next  impression.  Much  experience  is  neces- 
sary for  this  and  also  for  judging  of  the  amount  of  color  taken  from 
the  daubing  pad  by  the  block.  At  the  present  time,  block  printing 
is  generally  used  only  for  very  large  designs;  those  containing 
a  great  variety  of  colors  may  be  printed  thus,  but  a  separate  block 
is  necessary  for  each  color  used ;  and  since  one  block  usually  serves 
only  for  a  part  of  the  whole  design,  several  blocks  may  be  needed 
for  each  color.  Thus  the  process  is  very  slow  and  laborious,  making 
it  expensive. 

Roller  or  machine  printing  has  now  generally  replaced  all  other 
processes.  One  engraved  copper  roll  is  employed  for  each  color  in 
the  design,  except  in  a  few  cases  where  a  color  is  produced  by  print- 
ing one  over  another,  as  a  yellow  over  a  blue  to  make  green.  The 
design,  drawn  by  the  artist,  is  enlarged  several  times  and  engraved 
on  a  zinc  plate.  The  copper  roll  is  turned  perfectly  true  in  a  lathe, 
and  then  polished.  Its  surface  is  coated  with  wax  or  a  special 
varnish,  through  which  the  design  is  scratched  by  a  stylus  of  a 
pantagraph  machine,  following  the  pattern  on  the  zinc  plate ;  this 
reproduces  the  design  and  at  the  same  time  reduces  it  to  the  required 
size.  The  roll  is  then  etched  with  nitric  acid,  until  the  figures  have 
the  necessary  depth.  After  washing  off  the  acid,  the  wax  is  re- 
moved, and  the  hollow  roll  is  slipped  on  a  mandrel  for  use  in  the 
machine.  The  color  is  fed  to  the  print  roll  from  the  color  box  by 
a  revolving  cylindrical  brush  called  the  "  furnisher,"  which  dips  into 
the  color  paste.  This  covers  the  entire  surface  of  the  roll  with  the 
color  and  fills  the  depressions  of  the  design.  A  sharp  steel  blade, 
called  the  "doctor,"*  rubs  against  the  surface  of  the  roll  as  the 
latter  revolves,  and  scrapes  off  all  excess  of  color,  leaving  only 
that  contained  in  the  depressions  of  the  pattern.  Beneath  the 
cloth  a  similar  blade  rubs  the  roll,  removing  from  it  any  bits  of 
dirt  or  lint  which  may  adhere  after  the  cloth  has  been  printed. 
The  print  rolls  are  all  set  around  one  central  drum  called  the 
"bowl,"  against  which  they  press,  and  which  is  covered  with 
several  thicknesses  of  strong  linen  and  woollen  cloth  called  "lap- 
ping," which  will  withstand  the  repeated  pressure  without  breaking. 
This  lapping  must  be  very  evenly  placed,  or  streaks  will  appear  on 
the  printed  goods.  The  cloth  to  be  printed  passes  between  the  rolls 
and  the  bowl,  considerable  pressure  being  brought  to  bear  upon  it, 
so  that  it  is  forced  into  the  engraving  on  the  roll  and  takes  out  all 
the  color.  Between  the  lapping  and  the  cloth  to  be  printed,  an 

*  In  order  that  irregularities  may  not  be  worn  in  the  edge  of  the  doctor  or  on  the 
print  roll,  the  former  is  given  a  slight  sidewise  movement  by  a  suitable  gearing. 


496  OUTLINES  OF   INDUSTRIAL   CHEMISTRY 

endless  band  or  "  blanket "  of  thick  woollen  cloth  passes.  This  adds 
to  the  elasticity  of  the  lapping,  affording  a  better  impression  of  the 
engraving,  and  protecting  the  lapping  from  color  and  moisture. 
The  blanket  is  often  40  to  50  yards  long,  and  goes  over  drying 
drums  before  it  passes  around  the  bowl.  In  order  to  keep  the 
blanket  free  from  color  stains,  a  piece  of  unbleached  cotton  cloth, 
called  "  gray  cloth "  or  "  back  cloth,"  is  interposed  between  it  and 
the  print  cloth.  This  gray  cloth  is  sometimes  used  once  or  twice 
for  this  purpose  and  then  sent  to  the  singeing  and  bleaching  process, 
after  which  it  is  itself  printed,  usually  with  a  dark  color.  Thus 
three  long  webs  of  cloth  pass  between  the  rolls  and  the  bowl  at 
once,  —  the  blanket,  back  cloth,  and  print  cloth. 

The  printing  colors  may  be  soluble  dyestuffs  or  insoluble  pig- 
ments made  into  a  paste  with  water,  oil,  or  other  medium ;  in  many 
cases  mordants  alone  are  printed  on  the  fabric.  It  is  also  essential 
that  the  color  pastes  shall  contain  some  material  by  which  the  pig- 
ments may  be  fixed  on  the  fibre  so  that  they  will  not  rub  off  in  the 
finishing  operations.  In  order  that  the  printing  colors  may  adhere 
to  the  rolls  and  not  run  when  applied  to  the  cloth,  thickening  agents 
are  employed.  The  most  important  of  these  are  British  gum,  starch, 
flour,  gum  arabic,  Senegal,  or  tragacanth,  and  blood  or  egg  albumin. 
It  is  necessary  that  these  shall  not  form  any  chemical  combination 
with  the  color  or  the  mordants.  Some  thickeners  are  insoluble  in 
cold  water,  while  others  are  more  or  less  soluble,  and  the  printer 
must  select  that  best  adapted  to  his  purpose  and  the  color  he  wishes 
to  use.  The  preparation  of  color  pastes  is  called  "  color  mixing " 
and  requires  much  care.  The  ingredients  are  mixed  in  special  ves- 
sels called  "  color  pans,"  these  being  jacketed  copper  kettles  which 
may  be  heated  by  steam  or  cooled  by  water,  as  required.  If  starch 
or  flour  is  used,  it  must  be  very  well  boiled  to  a  smooth  paste  before 
the  color  is  stirred  in.  British  gum  and  Senegal  are  dissolved  in 
hot  water  with  constant  stirring,  while  tragacanth  is  boiled  for 
several  hours.  Albumin  is  dissolved  in  water  at  less  than  50°  C., 
while  stirring  constantly.  After  mixing,  the  color  paste  must  be 
strained  to  remove  any  lumps,  dirt,  or  grit,  and  to  form  a  smooth 
paste  of  homogeneous  character.  For  large  lots,  this  is  sometimes 
done  by  machinery,  but  in  most  cases  the  straining  cloth  is  folded 
over  the  paste  like  a  bag,  and  then  twisted  by  hand  by  the  work- 
men, thus  forcing  the  paste  through  the  cloth.  It  is  now  ready  to 
put  into  the  color  boxes  of  the  machine,  from  which  the  furnisher 
roll  feeds  it  to  the  print  roll. 

But  the  color  is  not  always  printed  on  the  goods.     Sometimes 


TEXTILE   INDUSTRIES  497 

only  the  mordants,  mixed  in  the  thickener,  are  printed,  the  goods 
being  afterwards  immersed  in  the  dye-bath,  and  taking  the  color 
only  where  mordanted.  Or  a  substance  called  a  "  resist "  is  printed 
to  prevent  the  dye  from  taking  the  fibre  in  the  printed  portions ; 
thus  white  spots  or  figures  are  left  on  a  colored  background.  Or 
"  discharges "  may  be  printed  on  dyed  material,  destroying  or 
bleaching  the  color  where  they  touch. 

After  printing,  the  cloth  is  dried  by  passing  above  a  series  of 
steam  boxes,  or  hot  pipes,  but  generally  not  close  enough  to  touch 
them,  lest  some  of  the  colors  should  be  changed  by  the  heat.  With 
many  colors,  however,  the  drying  is  done  more  quickly  by  passing 
the  print  over  a  steam-heated  roll  or  "  drying-can."  For  pigments 
in  albumin  thickening,  this  direct  drying  is  sufficient  to  fix  the 
color  on  the  fibre,  and  the  goods  may  be  finished  at  once. 

The  method  of  producing  the  colored  design  in  calico  printing  is 
called  a  "  style."  The  following  are  the  most  important :  pigment 
style,  steam  style,  madder  or  dyeing  style,  oxidation  style,  discharge 
style,  and  resist  style.  The  pigment  style  is  now  of  less  importance 
than  it  formerly  was.  Insoluble  pigments,  such  as  ultramarine, 
Guignet's  green,  chrome  yellow,  vermilion,  etc.,  are  mixed  with  the 
thickening  paste,  printed  directly,  and  the  print  dried  by  passing 
over  a  hot  roll.  If  the  thickening  employed  is  gum,  starch,  or  dex- 
trine, the  resulting  print  is  not  fast  to  washing,  and  is  known  as 
"  loose  pigment  style."  But  if  blood  or  egg  albumin  is  used,  and  the 
print  dried  at  a  high  temperature,  or  steamed  to  coagulate  the  al- 
bumin, the  color  is  fixed  on  the  fibre,  and  is  fast  to  ordinary  wash- 
ing and  soaping. 

The  steam  style,  formerly  called  the  extract  style,  is  used  for 
those  colors  in  which  the  mordant,  dyestuff,  and  thickening  can  be 
mixed  cold  or  at. moderate  temperatures  without  the  formation  of 
the  color  lake.  Very  often  acetic  acid  is  added  to  retard  the  action 
between  the  dyestuff  and  mordant.  Tannic  acid  is  much  used  as  a 
mordant  in  steam  colors.  The  cloth  is  generally  prepared  by  oiling 
it  slightly  with  Turkey-red  oil,  or  "oleine,"  before  printing.  The 
printed  cloth  is  usually  arranged  on  racks  on  a  car  which  can  be  run 
directly  into  the  steamer,  or  the  goods  are  made  to  pass  through  a 
continuous  steamer,  consisting  of  a  large  closed  vessel  containing 
numerous  rollers  at  the  top  and  bottom,  over  which  the  cloth  passes 
up  and  down  many  times.  The  steam  is  under  3  to  10  pounds 
pressure,  whereby  the  acetic  acid  vaporizes,  the  reaction  between 
the  mordant  and  dyestuff  is  brought  about,  and  the  color  developed 

2K 


498  OUTLINES  OF  INDUSTRIAL   CHEMISTRY 

on  the  fibre.  The  print  is  now  washed  in  a  soap  bath  to  remove 
the  thickening. 

When  basic  dyes  and  tannic  acid  are  used,  the  printed  and 
steamed  goods  are  passed  through  a  bath  of  tartar  emetic  or  other 
antimony  salt,  to  fix  the  color  on  the  fibre. 

Steam  style  is  now  very  generally  used,  and  with  many  dye-stuffs. 

In  the  madder  or  dyeing  style,  only  the  mordant  is  printed,  and 
fixed  on  the  fibre  by  drying,  steaming,  or  aging.  The  goods  are 
usually  "dunged"  in  a  bath  of  cow-dung  and  chalk,  to  remove 
excess  of  mordant  from  the  surface  of  the  fibre,  and  thus  prevent 
its  spreading  to  the  unprinted  portions  of  the  cloth  and  blending  the 
figures.  Arsenate  of  soda  was  formerly  used  for  this  purpose,  but 
recently  phosphate  of  soda  has  been  largely  substituted.  After 
dunging,  the  goods  are  thoroughly  washed,  and  at  once  dyed  in  an 
alizarin  or  madder  bath.  With  different  mordants  these  give  dif- 
ferent shades ;  thus  alumina  yields  reds  and  pinks ;  tin  gives  scarlet ; 
chromium,  maroon ;  and  iron,  chocolate  or  brown.  But  the  number 
of  colors  obtained  in  this  way  is  limited,  and  the  process  is  largely 
given  up  in  favor  of  the  more  convenient  steam  style. 

The  oxidation  style  is  chiefly  used  for  aniline  blacks.  The  goods 
are  printed  with  a  paste  containing  aniline  salt,  sodium  or  potassium 
chlorate,  and  usually  a  trace  of  vanadium  salt,  all  worked  into  a 
suitable  thickening.  After  printing,  the  goods  are  "aged"  for  two 
days,  or  for  a  short  time  in  a  steam  "  ager,"  and  are  passed  through 
a  potassium  bichromate  solution  at  70°  C. ;  they  are  then  washed  in 
a  hot  soap  solution.  Manganese  browns  for  backgrounds  are  some- 
times printed  by  padding  the  surface  of  the  cloth  with  manganous 
chloride  or  sulphate,  and,  after  drying,  padding  again  with  caustic 
soda.  The  cloth  is  then  washed  and  passed  into  a  solution  of 
bleaching  powder,  whereby  a  hydrated  peroxide  of  manganese  is 
formed  on  the  fibre  as  a  uniform  brown  color.  This  is  then  printed 
again  by  the  discharge  style  to  produce  a  figured  pattern. 

In  the  discharge  style,  the  dyed  cloth  is  printed  Avith  a  discharge 
paste,  leaving  a  white  figure  on  a  colored  ground.  Or  it  is  often  cus- 
tomary to  add  some  color  to  the  paste  which  is  not  affected  by  the 
discharge,  and  which  remains  on  the  goods  where  printed ;  e.g.  certain 
pigments,  such  as  chrome  yellow,  Guignet's  green,  and  vermilion. 
Thus  colored  figures  are  obtained  on  a  ground  of  different  color. 
Common  discharges  are  stannous  chloride,  zinc  dust  and  sodium 
bisulphite,  or  sodium  bichromate,  the  last  being  used  in  connection 
with  a  sulphuric  acid  bath.  Tartaric,  citric,  and  oxalic  acids  are  also 
used  as  discharges,  acting  on  the  mordants  to  render  them  soluble  in 


TEXTILE   INDUSTRIES  499 

the  printed  portions,  whence  they  are  removed  by  washing,  so  that, 
in  subsequent  dyeing,  the  color  does  not  take  the  fibre  in  these  spots. 
Alkaline  discharges,  made  with  caustic  soda  and  potassium  ferri- 
cyanide,  or  potassium  bichromate  and  caustic  soda,  are  used  with 
indigo. 

In  the  resist  style,  substances  are  printed  on  the  cloth  which 
prevent  the  fixing  of  the  mordant  or  color  in  the  printed  portions. 
Thus,  when  dyed,  the  printed  pattern  appears  white  on  a  colored 
ground.  Resists  may  act  mechanically  or  chemically.  Those  of  the 
first  kind  are  generally  oils  or  resins  with  china  clay,  which  are 
insoluble  and  prevent  access  of  the  dyestuff  to  the  fibre.  Chemical 
resists  are  generally  citrate  of  sodium,  or  acetate  of  calcium,  the 
former  being  preferred  for  preventing  the  fixing  of  alumina  or  iron 
mordants,  and  the  latter  to  hinder  the  development  of  aniline  blacks. 
After  printing,  the  cloth  is  dunged,  washed,  and  dyed.  For  resists 
on  indigo  dyed  goods,  the  cloth  is  printed  with  zinc  sulphate  or 
copper  sulphate. 

In  all  styles  where  the  cloth  is  dyed  after  printing,  the  white 
parts  of  the  figure  are  usually  discolored  by  the  dye,  and  it  becomes 
necessary  to  "  clear  "  them,  generally  by  "  chemicking  "  in  a  solution 
of  bleaching  powder  so  dilute  as  not  to  affect  the  color  in  the  mor- 
danted parts  of  the  goods.  This  is  followed  by  a  thorough  soaping 
and  washing.  The  printed  calico  is  usually  finished  by  starching, 
bluing  slightly  to  improve  the  appearance  of  the  white,  tendering, 
and  finally  calendering  between  hot  rolls. 

Wool  is  extensively  printed  for  delaines  and  challis,  the  steam 
and  discharge  styles  being  most  commonly  employed.  It  is  usually 
prepared  for  printing  by  passing  through  bleaching  powder  liquor, 
and  then  through  an  acid  bath,  the  chlorine  imparting  to  the  wool  a 
greater  affinity  for  the  acid  colors.  The  color  is  prepared  with 
thickening,  much  as  for  cotton,  and  after  printing  the  cloth  is 
usually  steamed  and  washed.  Direct  and  basic  colors  are  printed 
without  further  addition  to  the  paste;  acid  colors  require  a  little 
oxalic  or  tartaric  acid ;  for  mordant  colors,  acetate  of  chromium  or 
of  aluminum  is  employed,  while  for  discharge  styles  stannous  salts 
are  used  as  reducing  agents  in  the  paste. 

Silk  is  printed  in  much  the  same  way  as  wooL  It  is  usually 
mordanted  with  tin,  and  sometimes  with  an  acid. 


500  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 


REFERENCES 

Die  Rohstuffe  des  Pflanzenreiches.    J.  Wiesner,  Wien,  1873. 

Dyeing  and  Calico  Printing.     F.  Crace-Calvert,  Manchester,  1876.     (Palmer 

&  Howe.) 

Etudes  sur  les  Fibres  ve"getales  textiles.     M.  Ve'tillard,  Paris,  1876. 
Le  Conditionneraent  de  la  Soie.     Jules  Persoz,  Paris,  1878. 
Calico  Printing,  Bleaching,  r.nd  Dyeing.     C.  O'Neill,  London,  1878. 
Bleicherei,  Farberei  und  Appretur.     C.  Romen,  Berlin,  1879. 
Die  Gewinnung  der  Gespinnstfasern.     H.  Richard,  Braunschweig,  1881. 
The  Wild  Silks  of  India.     Thomas  Wardle,  London,  1881. 
Die  Technologic  der  Gespinnstfasern.     2  Bde.     H.  Grothe,  Berlin,  1882. 
Die  Wascherei,  Bleicherei  und  Farberei  von  Wollengarnen.     R.  Sachse,  Leip- 
zig, 1882. 

Dyeing  and  Tissue  Printing.    W.  Crookes,  London,  1882.     (Bell  &  Sons.) 
Structure  of  the  Cotton  Fibre.     F.  Bowman,  Manchester,  1882. 
Ramie,  Rhea,  Chinagras  und  Nesselfaser.     Bouche"  u.  Grothe,  Berlin,  1882. 
Trait^  pratique  du  De"graissage,  etc.     A.  Gillet,  Paris,  1883. 
Ueber  pflanzliche  Faserstoffe.     F.  von  Hohnel,  Wien,  1884. 
Bleaching,  Dyeing,  and  Calico  Printing.     J.  Gardner,  London,  1884. 
The  Dyeing  of  Textile  Fabrics.     J.  J.  Hummel,  London,  1885.    (Cassell  &  Co.) 
The  Structure  of  Wool  Fibre.     F.  J.  Bowman.     2d  Ed.    Manchester,  1885. 

(Palmer  &  Howe.) 
Les  Soies.     N.  Rondot,  Paris,  1885. 
The  Printing  of  Cotton  Fabrics.    A.  Sansone,  Manchester,  1887.     (Heywood 

&  Son.) 
Report  on  Indian  Fibres  and  Fibrous  Substances.    C.  F.  Cross,  E.  J.  Bevan, 

C.  M.  King,  and  E.  Joynson,  London,  1887. 
Microscopic  der  Faserstoffe.     F.  von  Hohnel,  Wien,  1887. 
Dyeing.     A.  Sansone,  Manchester,  1888.     (Heywood  &  Son.) 
Das  Fa'rben  und  Bleichen  von  Baumwolle,  Wolle,  Seide,  Jute,  u.s.w.    J.  Kerz- 

feld,  Berlin,  1889. 
Die  Echtfarberei  der  losen  Wolle  in  ihrem  ganzen  Uinfange.    Alfred  Delmart. 

3  Bde,  1887-1891.     Reichenberg  i.  B. 
Die  Jute  und  ihre  Verarbeitung.    E.  Pfuhl.     3  Bde.     Berlin,  1888-1891.     (J. 

Springer.) 

Handbuch  der  Farberei.    A.  Ganswindt,  Weimar,  1889. 
L'Industrie  de  la  Teinture.     C.  L.  Tassart,  Paris,  1890.     (Bailliere  et  Fils.) 
The  Cotton  Fibre,  Its  Structure,  etc.     Hugh  Monie,  Manchester,  1890. 
Report  on  Flax,  Hemp.  Ramie,  etc.    U.  S.  Dep't  Agriculture,  Washington,  1890. 
Le  Soie.     L.  Vignon,  Paris,  1890. 
Industrie  de  la  Soie.    F.  Debaitre,  Paris,  1890. 
Traite  de  Teinture  sur  laine  et  sur  etoffes  de  laine.    P.  F.  Levaux,  Liege,  1890. 

(J.  GoJenne.) 

Traite'  Pratique  de  Teinture  et  Impression.    M.  de  Vinant.    2d  Ed.   Paris,  1891. 
Die  chemische  Technologic  der  Gespinnstfasern.     O.  N.  Witt,  Berlin,  1891. 
Tintura  della  Seta.    Teodoro  Pascal,  Milano,  1892.     (U.  Hoepli,) 
Traite'  de  la  Teinture  et  de  1'Impression.      J.  Depierre,  Paris,  1891-1892.    2 

Tomes.     (Baudry  et  Cie.) 


PAPER  501 

Die  Praxis  der  Farberei  von  Baumwolle  u.s.w.    J.  Herzfeld,  Berlin,  1892. 

Silk  Dyeing,  Printing,  and  Finishing.    J.  H.  Hurst,  London,  1892.    (George  Bell 

&  Sons.) 

Textiles  Ve>etaux.     E.  Lecornpte,  Paris,  1893. 
Manuel  of  Dyeing.     E.   Knecht,  C.   Rawson,  and  R.  Loewenthal.     3  Vols. 

London,  1893.     (Griffin  &  Co.) 
La  Pratique  du  Teinturier.     Jules  Jar§on,  Paris,  1894.     2  Toines.     (Gauthier- 

VillarsetFils.) 

Cellulose.     Cross  &  Bevan,  London,  1895. 
Bleichen  u.  Farben  der  Seide  u.  Halbseide.     C.  H.  Steinbeck,  Berlin,  1895. 

(J.  Springer.) 
Bleaching  and  Calico  Printing.     Geo.  Duerr  and  Wm.  Turnbull,  London,  1896. 

(Griffin  &  Co.) 
The  Cotton  Plant.     Bulletin  No.  33,  U.  S.  Dep't  of  Agriculture,  Washington, 

D.C.,  1896. 
Das  Anthracene  und  seine  Derivate.     G.  Auerbach.     2te  Auf.     Braunschweig, 

1880. 

Die  Industrie  der  Theerfarbstoffe.     C.  Haussermann,  Stuttgart,  1881. 
Die  Chemie  des  Steinkohlentheers.     G.  Schultz.     2te  Auf.     2  Bde.     Braun- 
schweig, 1886. 

Die  kiinstlichen  organischen  Farbstoffe.    P.  Julius,  Berlin,  1887. 
The  Chemistry  of  the  Coal-Tar  Colours.    R.  Benedikt,  translated  by  E.  Knecht. 

2d  ed.     London,  1889.     (Bell  &  Sons.) 
Organische    Farbstoffe,   welche    in    der    Textilindustrie    Verwendung  finden. 

R.  Mohlau,  Dresden,  1890.     (Julius  Bloem.) 
Les  Matieries  colorantes,  etc.     C.  L.  Tassart,  Paris,  1890. 
Tabellarische  Uebersicht  der  kiinstlichen  organischen  Farbstoffe.    Schultz  & 

Julius.     2te  Auf.     Berlin,  1891. 

Chemistry  of  the  Organic  Dyestuffs.     R.  Nietzki,  translated  by  Collin  &  Rich- 
ardson, London,  1892. 

Cheinie  der  organischen  Farbstoffe.     R.  Nietzki.     2te  Auf.     Berlin,  1894. 
Tabellarischen  Uebersicht  der  kiinstlichen  organischen  Farbstoffe.    A.  Lehne, 

Berlin,  1894. 


PAPER 

Paper  consists  of  cellulose  fibres  matted  or  felted  into  a  coherent 
sheet.  Usually  a  certain  amount  of  mineral  matter,  or  "  loading  " 
is  incorporated  with  the  paper  to  increase  the  weight  and  render  it 
smooth  and  less  porous.  The  raw  materials  furnishing  the  fibre  are 
wood  pulp,  cotton  or  linen  rags,  esparto,  straw,  hemp,  flax,  jute,  etc. 
Old  paper  and  the  trimmings  and  waste  from  paper  mills  are  also 
reworked.  The  common  loading  materials  are  clay  (kaolin),  ground 
talc  or  steatite,  gypsum,  or  precipitated  calcium  sulphate  (pearl 
hardening,  crown  filler,  etc.),  and  barium  sulphate  (blanc  fixe). 

In  nearly  every  case  the  cellulose  fibres  must  be  freed  from  in- 


502  OUTLINES  OF  INDUSTRIAL   CHEMISTRY 

crusting  matter  and  treated  in  such,  a  way  as  to  reduce  the  substance 
to  a  state  of  minute  subdivision  and  to  isolate  more  or  less  com- 
pletely the  individual  fibres.  It  is  largely  in  this  isolation  that 
chemical  processes  are  involved  in  the  industry. 

Wood  pulp  is  made  from  poplar  (Populus  grandidentata,  Michx.), 
spruce  (Picea  rubra,  Link.),  hemlock  (Tsuga  Canadensis,  Carr.),  pine 
(Pinus  Strobus,  L.),  cotton  wood  (Populus  monilifera,  Ait.),  basswood 
(Tilia  Americana,  L.),  white  birch  (Betula  papyrifera),  and  maple 
(Acer  dasycarpum,  Ehrh.). 

Wood  pulp  is  of  two  kinds,  mechanical  and  chemical.  Mechani- 
cal pulp  is  made  by  forcing  a  large  stick  of  wood  against  a  revolving 
sandstone,  or  emery  wheel,  over  which  a  jet  of  water  plays  continu- 
ously. The  resulting  pulp  is  washed  away  by  the  water  and  passes 
several  screens  to  remove  insufficiently  disintegrated  particles.  The 
mixture  of  pulp  and  water  then  flows  into  a  tank  in  which  a  cylin- 
der covered  with  wire  gauze  is  revolving.  The  water  passes  through 
and  a  layer  of  pulp  adheres  to  the  cylinder  and  is  delivered  onto  an 
endless  blanket ;  this  carries  it  to  a  pair  of  squeeze-rolls  where  it  is 
compacted.  It  is  then  cut  into  sheets  of  convenient  size,  several  of 
which  are  pressed  into  one  thick  "  board  "  for  transportation.  Me- 
chanical pulp  is  contaminated  with  lignin  and  resinous  matters, 
which  turn  brown  on  exposure  to  light.  The  fibres  are  short  and  do 
not  mat  together  well,  so  the  paper  made  from  it  is  not  strong ;  such 
pulp  is  only  used  for  cheap  paper  (e.g.  newspaper)  and  generally  in 
conjunction  with  other  fibres  and  chemical  pulp.  By  dipping  a 
strip  of  paper  into  a  solution  of  phloroglucin  in  hydrochloric  acid, 
the  presence  of  ground  pulp  may  be  detected  by  the  appearance  of  a 
magenta  red  color ;  an  aqueous  solution  of  aniline  sulphate  will  yield 
a  yellow  color. 

Chemical  pulp  is  prepared  by  the  soda  process,  the  sulphite  process, 
or  by  the  sulphate  process.  The  soda  process  is  largely  used  for  soft 
woods,  especially  poplar,  cotton  wood,  and  basswood.  The  bark  is  re- 
moved by  hand  shaves,  but  the  knots  and  rotten  wood  are  generally 
disregarded.  The  wood  is  put  through  a  chipping  machine  which  cuts 
it  across  the  grain  and  reduces  it  to  fragments  about  three-eighths  of 
.an  inch  thick.  After  the  chips  are  dusted  by  blowing  them  against  a 
screen,  they  are  filled  into  the  digesters.  These  consist  of  rotary 
horizontal  cylinders  holding  about  3  cords  of  wood,  or  rotary  globular 
boilers,  holding  about  5  cords.  Recently,  upright  fixed  digesters 
heated  by  live  steam  have  come  into  general  use.  The  digester  is 
nearly  filled  with  chips,  which  are  then  covered  with  a  caustic  soda 
liquor  of  about  11°  Be.  They  are  boiled  for  from  8  to  10  hours  at  a 


PAPER  503 

pressure  of  from  90  to  110  pounds.  The  effect  of  this  "  cooking  "  is  to 
reduce  the  wood  to  a  soft  mass  of  grayish  brown  color,  while  the 
liquor  has  become  dark  brown  and  has  a  density  of  lli°  Be.  The 
non-cellulose  matters  of  the  wood  (lignin,  resins,  etc.)  which  consist 
largely  of  organic  acids,  are  decomposed  by  or  combine  with  the  soda, 
and  consequently  the  alkali  is  nearly  all  neutralized  during  the  pro- 
cess. The  pulp  and  "black  liquor"  are  blown  out  into  a  tank  having 
a  sloping  bottom  and  covered  with  a  closely  fitting  lid.  Here  the  pulp 
is  systematically  washed  and  the  wash-waters  are  saved  until  their 
density  falls  below  8°  or  9°  Be.  The  liquor  is  pumped  into  a  mul- 
tiple effect  evaporator  and  evaporated  to  38°  Be.,  when  it  is  sent 
directly  to  a  revolving  calcination  furnace  (p.  4)  from  which  a  dry 
soda-ash  is  recovered ;  this  is  recausticized  for  use  in  the  digesters. 
From  85  to  90  per  cent  of  the  original  soda  is  thus  recovered. 

The  caustic  soda  has  a  direct  action  on  the  cellulose  itself,  espe- 
cially when  the  pressure  is  high ;  hence  some  of  the  fibre  is  dissolved 
or  destroyed,  while  all  of  it  is  weakened  somewhat.  The  pulp  pro- 
duced is  very  soft,  and  though  of  a  dark  color,  is  easily  bleached. 
The  yield  from  poplar  is  about  40  per  cent  of  the  weight  of  the 
wood. 

In  the  sulphite  process,  the  wood  (generally  coniferous  wood)  is 
boiled  under  pressure  with  sulphurous  acid  or,  more  commonly,  with 
acid  sulphite  of  calcium  and  magnesium.  The  action  of  the  sulphur- 
ous acid  under  pressure  and  at  a  high  temperature  upon  the  lignin 
and  other  incrusting  matters  of  the  wood  fibre  is  probably  a  hydrol- 
ysis ;  by  this,  these  complex  molecules  are  broken  down,  the  result- 
ing products  being  largely  organic  acids  and  aldehydes,  soluble  in 
the  liquor.  But,  owing  to  secondary  reactions  among  themselves, 
certain  acids  and  insoluble  tar-like  substances  are  also  formed, 
which  the  reducing  nature  of  the  sulphurous  acid  does  not  appear  to 
entirely  prevent.  The  acid  sulphites  react  much  like  sulphurous 
acid,  but  the  bisulphites  combine  with  the  aldehydes  formed  in  the 
first  stage  of  the  decomposition,  producing  stable  and  soluble  double 
salts.  The  organic  acids  which  are  also  formed  decompose  the 
bisulphites  and  form  soluble  calcium  and  magnesium  salts,  while 
sulphurous  acid  gas  is  set  free,  causing  a  constant  increase  in  the 
pressure  within  the  digester.  The  acid  sulphites  also  tend  to  bleach 
the  coloring  matter  of  the  fibres  by  forming  colorless  compounds 
with  them,  but  this  is  a  very  unstable  bleach  and  the  original  color 
soon  returns  when  the  pulp  is  made  into  paper.  Hence  for  perma- 
nent whiteness  the  pulp  is  further  bleached  with  chlorine.  Bisul- 
phite of  calcium  is  unstable  and  decomposes  readily  into  neutral 


504  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

sulphite,  setting  free  sulphurous  acid.  This  results  in  the  precipi- 
tation of  the  neutral  sulphite  on  the  fibre,  which  is  left  harsh,  even 
after  long  washing.  Magnesium  bisulphite  is  more  stable,  and, 
although  less  corrosive  to  the  fibre,  it  dissolves  the  non-cellulose 
matter  even  more  completely  than  does  the  lime  salt ;  further,  any 
sulphate  or  neutral  sulphite  which  may  be  formed  is  easily  washed 
off  and  the  pulp  is  left  soft  and  white.  Sodium  bisulp'hite  gives  a 
better  product  than  either  of  the  above,  and  strong  liquors  can  be 
made  from  it ;  but  it  is  too  expensive  for  general  use. 

Bisulphite  liquors  are  made  by  passing  sulphur  dioxide  through 
towers  packed  with  dolomite,  over  which  water  is  trickling ;  or  by 
leading  sulphur  dioxide  into  closed  vessels  about  half  full  of  milk 
of  lime  (prepared  from  dolomite).  Within  the  vessel  is  a  system  of 
revolving  paddles,  half  submerged  in  the  liquor,  and  thus  presenting 
large  surfaces,  wet  with  the  liquor,  to  the  action  of  the  gas ;  they 
also  splash  the  spray  into  the  atmosphere  of  gas,  thus  securing  rapid 
and  complete  absorption.  Usually  a  series  of  three  of  these  tanks 
are  used,  the  strong  gas  entering  the  most  concentrated  liquor,  which 
is  thus  brought  up  to  a  gravity  of  about  1.045  to  1.060  (6°  to  8°  Be.), 
and  containing  3^  to  4^  per  cent  S02.  The  sulphur  dioxide  is  pre- 
pared by  burning  brimstone  in  an  iron  retort.  Much  care  is  neces- 
sary in  regulating  the  air  supply  to  the  burner;  too  much  air  forms 
S03,  which  produces  sulphates  in  the  liquor;  it  also  causes  over- 
heating of  the  furnace,  and  consequent  sublimation  of  sulphur  into 
the  cooling  pipes  and  absorption  tanks,  where  polythionic  acids 
(thiosulphates)  are  formed.  These  precipitate  sulphur  in  the  pulp 
in  the  digester,  and  cause  trouble  in  the  paper  making.  Too  little 
air  supplied  to  the  burner  also  causes  sublimation  of  sulphur.  The 
hot  gases  from  the  burner  are  cooled  to  10°  or  15°  C.  by  passing 
through  water-cooled  lead  pipes.  For  the  strongest  liquor,  the  tem- 
perature in  the  absorption  tanks  must  be  kept  as  low  as  possible. 
The  tanks  for  storing  the  sulphite  liquors  are  sometimes  lined  with 
lead,  though  unlined  tanks  of  hard  pine  are  often  used.  Large 
quantities  of  liquor  may  be  kept  without  much  loss  of  strength,  either 
through  oxidation  to  sulphate,  or  evolution  of  gas  and  precipitation 
of  sulphite.  Bronze  rotary  pumps  or  lead-lined  acid  eggs  are  used 
for  pumping  the  liquor. 

Sulphite,  digesters  are  usually  made  of  steel  and  lined  with  3  to 
4  inches  of  neat  Portland  cement,  or  with  a  mixture  of  Portland 
cement  and  sand,  faced  with  a  layer  of  hard-burned,  acid-resisting 
brick.  The  acid  liquors  have  a  very  corrosive  action  on  iron,  and 
much  experimenting  has  been  done  to  find  a  metal  lining  suitable 


PAPER  505 

for  this  use.  Lead  resists  the  action  very  well,  but  when  used  as 
a  lining  it  soon  cracks  or  warps.  It  also  gives  much  trouble  through 
its  tendency  to  "  crawl,"  and  has  been  abandoned  in  favor  of  cem- 
ent. By  filling  the  digester  entirely  full  of  liquor  and  heating, 
a  layer  of  calcium  sulphite  may  be  deposited  as  scale  on  the  walls, 
and  afford  much  protection  to  the  iron.  Bronze  digesters  have  also 
been  tried,  but  are  too  expensive,  do  not  resist  the  liquor,  and  are 
lacking  in  strength,  several  having  exploded.  Two  types  of  digester 
are  now  in  use,  the  rotary  and  the  upright.  The  former  are  usually 
large,  globular  vessels,  heated  by  free  steam,  introduced  through  the 
hollow  trunnions.  Live  steam  must  be  as  dry  as  possible,  to  avoid 
diluting  the  liquor  too  much.  The  digesters  have  manholes,  and  also 
suitable  blow-off  valves  for  the  escape  of  gas,  if  the  pressure  be- 
comes too  high. 

For  making  sulphite  pulp,  all  bark,  knots,  and  dead  wood  are  cut 
out  of  the  sticks,  which  are  then  chipped  across  the  grain,  as  for 
soda  pulp.  The  boiling  is  carried  on  by  the  " quick-cook"  or  the 
"  slow-cook  "  method.  In  the  quick-cook  system  the  digester  is  com- 
pletely filled  with  chips,  and  all  the  liquor  (about  1200  gallons  per 
cord  of  chips)  is  run  in  as  rapidly  as  possible,  through  a  large  pipe. 
As  a  rule  the  liquor  is  about  10°  Tw.  (7°  Be.),  with  31-  per  cent  S02. 
At  first  the  pressure  is  raised  slowly,  in  order  to  avoid  the  hammer 
effect  of  the  live  steam  coming  in  contact  with  the  cold  digester  con- 
tent, and  also  to  avoid  too  high  a  temperature  before  the  liquor  has 
penetrated  into  the  interior  of  the  chips ;  otherwise  the  wood  may  be 
burned,  and  rendered  brown  or  red.  The  temperature  (which  is  the 
most  important  factor  in  the  process)  should  not  exceed  300°  to 
312°  F.  (149°  to  156°  C.).  It  should  be  regulated  by  a  thermometer, 
since  no  dependence  can  be  placed  on  the  pressure  indications  as  a 
means  of  determining  the  conditions  within  the  digester.  During 
the  12  or  18  hours'  boiling,  considerable  gas  is  evolved,  and  there  is 
a  steady  increase  in  the  pressure,  which  reaches  75  to  85  pounds. 

In  the  slow-cook  process  a  very  large  digester  (14  by  45  feet), 
heated  by  lead  coils  in  the  lower  part,  is  used.  The  chips  are 
packed  evenly  in  the  digester,  and  wet  steam  at  100°  C.  is  introduced 
for  12  hours,  until  all  the  air  is  expelled  and  the  charge  heated  to 
100°  C.  No  pressure  is  used,  and  the  condensed  water  is  allowed  to 
flow  out  freely.  Then  the  manhole  and  outlet  cocks  are  closed,  and 
the  cold  liquor  of  1.042  sp.  gr.  is  run  in.  This  causes  a  partial  vac- 
uum, and  a  better  penetration  of  the  liquor  into  the  chips  is  secured. 
When  the  digester  is  almost  full  of  liquor,  the  heating  is  begun,  and 
raised  to  110°  as  rapidly  as  possible,  though  it  usually  requires  12 


506  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

hours.  The  steam  is  so  regulated  that  this  temperature  is  main- 
tained for  about  12  hours,  when  it  is  slowly  raised  to  120°  C.,  and  a 
maximum  pressure  of  about  50  pounds  is  secured.  The  total  time 
of  boiling  is  about  36  hours.  Usually  the  pulp  is  blown  out  of  the 
digester  into  a  draining  tank,  where  it  is  washed  with  pure  water. 
When  washed  in  the  digester,  as  is  sometimes  done,  cold  water  must 
be  run  in  at  once  after  the  liquor  is  drawn  off,  to  prevent  burning 
the  pulp  by  the  heat  radiated  from  the  digester  walls.  Pulp  which 
is  to  be  bleached  must  be  very  thoroughly  washed,  since  any  bisul- 
phite left  in  the  fibre  acts  as  an  "  antichlor,"  and  destroys  the  bleach 
liquor.  The  undecomposed  shives  must  be  removed  by  screening 
the  pulp  before  bleaching. 

Sulphite  pulp  has  longer  and  stronger  fibre  than  soda  pulp,  and 
is  lighter  colored,  some  samples  being  nearly  as  white  as  the  bleached 
pulp.  It  is  often  used  unbleached,  but  contains  some  dirt  and  has  a 
harsh  feel.  If  the  chips  have  not  been  entirely  covered  by  the 
liquor,  or  if  the  latter  has  been  weakened  by  too  much  gas  blown  off 
during  the  boiling,  the  pulp  may  be  burned,  and  black,  charcoal-like 
specks  appear  in  it.  The  waste  sulphite  liquors  are  light  brown 
color,  and  contain  much  extractive  matter  from  the  wood ;  their  dis- 
posal is  often  a  serious  matter,  and  it  has  been  suggested  *  that  they 
may  furnish  material  for  oxalic  or  pyroligneous  acid,  or  alcohol. 

The  sulphate  process  consists  in  boiling  wood  chips  in  an  iron 
vessel  at  from  75  to  150  pounds  pressure,  for  35  hours,  in  a  solution 
of  sodium  sulphate  at  12°  to  15°  Be.,  and  containing  some  caustic  soda 
and  carbonate.  During  the  boiling  the  sodium  sulphide  formed  by 
reduction  of  the  sulphate  prevents  oxidation  of  the  fibre,  hence  a 
good  yield  of  strong  fibre  is  obtained.  The  waste  liquor  is  evapo- 
rated, and  the  residue  is  calcined  (forming  some  sodium  sulphide) 
and  leached ;  the  solution  is  heated  with  milk  of  lime  until  partially 
causticized,  and  is  then  returned  to  the  boiler.  The  gases  and  liquors 
formed  have  a  very  offensive  odor.  The  pulp  is  soft  and  strong,  and 
is  mainly  prepared  from  spruce  and  fir. 

The  pulp  made  by  any  of  the  above  processes  is  now  sent  to 
the  "  Hollander,"  or  "  beating  engine  "  (Fig.  94).  This  is  an  oval 
tub  15  to  20  feet  long  by  3|  feet  deep,  and  having  a  vertical  par- 
tition called  the  "  mid-feather  "  extending  along  the  middle,  about 
two-thirds  of  its  length.  On  one  side  of  this  and  extending  across 
one-half  of  the  width  of  the  tub  is  a  large  roll  (A),  carrying  on  its 
circumference  a  number  of  knives  (C).  The  floor  is  curved  up- 
ward behind  the  roll  (A),  conforming  closely  with  its  curvature,  but 
*  Griffin  and  Little,  Chemistry  of  Paper  Making,  p.  271. 


PAPER 


507 


extending  only  about  half  its  height,  as  shown  at  (B).  From  this 
highest  point  the  floor  falls  away  to  the  level  of  the  rest  of  the 
tub  bottom.  Under  the  roll  is  the  "  bed-plate "  (D),  fitted  with 
knives  similar  to  those  on  (A).  (A)  is  revolved  in  the  direction 
shown  by  the  arrow,  and  the  pulp  is  drawn  in  between  the  roll  (A) 
and  the  curved  bottom  (D),  and  the  fibres  are  torn  apart.  It  then 
passes  over  the  back-fall  (B)  and  thence  around  through  the  passage 
on  the  other  side  of  the  mid-feather  to  the  front  of  the  roll  and  again 
passes  between  the  knives.  (A)  is  suspended  upon  adjustable  bear- 
ings so  that  the  distance  between  the  two  sets  of  knives  may  be 
regulated.  They  are  not  set  very  close  for  breaking  and  disintegrat- 


.  94. 


ing  the  washed  pulp,  as  it  is  not  desired  to  break  the  knots  and  un- 
decomposed  wood,  which  would  cause  dirt  and  shive  in  the  pulp. 

In  order  to  complete  the  washing  of  the  pulp  during  its  disinte- 
gration one  or  two  drum- washers  (E)  are  usually  placed  in  each  hoi- 
lander.  These  are  rotating  cylinders  covered  with  fine  wire  gauze 
and  divided  into  compartments  by  curved  partitions.  A  conical  tube 
passes  through  the  centre  of  the  drum,  the  narrow  end  being  towards 
the  mid-feather.  The  partitions  radiate  from  this  cone  to  the  wire 
gauze  periphery  of  the  drum.  The  outer  end  of  the  drum  is  solid, 
but  that  next  the  mid-feather  has  a  central  opening  (F),  through 
which  each  compartment  discharges  its  content  of  water  into  the 
trough  attached  to  the  mid-feather.  The  drum,  supported  in  adjusta- 
ble bearings,  is  partly  submerged,  and  the  water,  passing  through  the 
gauze,  is  caught  in  the  compartments  as  the  drum  rotates  and  dis- 
charged through  (F).  It  flows  into  the  trough  and  out  through  the 


508 


OUTLINES   OF  INDUSTRIAL   CHEMISTRY 


pipe  (G).  The  gauze  holds  back  the  pulp  which  again  passes  around 
the  mid-feather  to  the  roll  (A). 

Another  form  of  hollander,  requiring  less  floor  space,  is  shown  in 
Fig.  95.  In  this  the  pulp  passes  below  the  floor  and  back-fall  on  its 
return  to  the  front  of  the  roll.  The  machine  is  but  little  wider  than 
the  length  of  the  roll  (A),  the  washing  drum  (E)  being  directly  be- 
hind the  roll. 

After  breaking,  the  pulp  is  carried  by  a  strong  stream  of  water 
onto  a  sluice  or  inclined  way  having  a  number  of  transverse  slats 
across  the  bottom.  The  knots  and  lumps  lodge  against  these  ob- 
structions, while  the  fine  pulp  flows  on  with  the  water  to  the  bleach- 
ing tanks. 


Fm.  95. 


Rags,  both  cotton  and  linen,  are  largely  used  in  paper  making. 
These  are  collected  in  all  countries,  and  arrive  at  the  mill  in  various 
conditions  of  filth.  They  are  first  sorted  by  hand,  the  seams  cut 
open,  and  all  buttons,  metallic  hooks,  etc.,  removed.  The  dust  is 
then  beaten  out  in  machines  having  rapidly  revolving  arms,  and 
then  the  rags  are  cut  into  small  pieces  and  boiled  for  12  hours  or 
longer,  under  a  pressure  of  60  or  70  pounds,  in  rotary  horizontal 
cylinders,  or  in  horizontal  kiers  (p.  452),  with  5  to  18  per  cent  of 
milk  of  lime.  Sometimes  a  little  soda-ash  is  added  to  the  liquor  for 
colored  rags.  After  boiling  they  are  dumped  in  heaps  to  drain  and 
soften  for  a  day  or  two.  After  washing  with  hot  water,  they  are 
sent  to  the  pulping  machine. 

Esparto,  or  Spanish  grass,  is  derived  from  Lygeum  Spartum,  Loefl. 
and  Stipa  tenacissima,  L.  The  bast  fibres  are  similar  to  those  of 
straw,  bat  give  a  stronger  paper.  It  is  chiefly  used  in  Europe,  being 
too  expensive  to  compete  with  wood  pulp  in  this  country.  Esparto 
and  straw  are  boiled  with  caustic  soda  in  upright  digesters.  In 


PAPER  509 

rotary  boilers  the  fibre  forms  little  balls  ("fish  eggs  "),  which  cause 
little  spots  or  lumps  in  the  paper.  The  pressure  and  time  of  boil- 
ing vary.  The  waste  liquor  is  evaporated,  and  the  alkali  recovered 
(p.  503).  After  washing,  the  pulp  bleaches  well  with  bleaching  liquor. 
In  this  country,  straw  is  generally  boiled  with  lime  to  prepare  a  pulp 
for  strawboard. 

Jute  has  very  short  fibre,  so  the  fibre  bundles  are  not  separated, 
and  only  the  lime-boil  is  employed. 

The  bleaching  of  paper  pulp  is  done  by  agitation  with  a  weak 
calcium  hypochlorite  solution.  If  the  liquor  is  heated  to  90°  or 
100°  F.,  or  a  little  acid  added,  the  process  is  hastened.  Alum  forms 
aluminum  hypochlorite  with  bleaching  powder  solutions,  which  is 
very  effective ;  a  slightly  acid  alum  or  "  bleaching "  alum  is  com- 
monly used.  The  bleaching  is  carried  on  in  special  vessels  ("chests "), 
or  in  the  beating  engines  or  hoi  landers,  the  latter  giving  the  best 
results.  Only  a  clear  solution  of  bleaching  powder  should  be  used, 
so  that  no  dirt  be  introduced  in  the  insoluble  residue,  as  it  would 
cause  spots  in  the  paper.  Rags  require  the  least  bleaching  (2  to  5 
pounds  bleaching  powder  to  100  pounds  of  stock),  and  spruce  pulp 
the  most  (about  18  to  25  pounds  per  100  pounds  for  sulphite  spruce 
pulp).  As  soon  as  bleached,  the  process  should  be  stopped,  espe- 
cially if  the  liquor  has  been  heated ;  otherwise  the  fibre  is  liable 
to  be  chlorinated,  and  color  again  taken  up.  The  excess  of  hypo- 
chlorite in  the  pulp  is  washed  out  with  water,  or  is  destroyed  by 
adding  an  antichlor,  such  as  sodium  thiosulphate  (p.  45),  in  the 
beating  engine.  Neutral  calcium  sulphite  is  also  recommended,  but 
its  action  is  slow :  - 

Ca(C10)2  -}-  2  CaS03  =  2  CaS04  +  2  CaCl2. 

The  pulp  must  be  thoroughly  washed  after  bleaching,  even  when 
antichlors  are  used,  since  injurious  substances  may  be  left  in  the 
pulp.  The  action  of  the  antichlor  is  as  follows :  — 

2  Ca(C10)2  +  NaA08  +  H20  =  2  KaCl  +  2  CaS04  +  2  HC1 ; 
or,  in  dilute  solutions :  — 
Ca(C10)2  +  4  Na2S203  +  H20  =  2  Na2S406  +  2  NaOH  +  CaO  +  2  NaCl. 

Other  materials  than  bleaching  powder,  such  as  ozone,  hydrogen 
peroxide,  sulphurous  acid,  or  liquid  chlorine,  have  been  suggested 
for  bleaching,  but  as  yet  these  are  of  much  less  importance  than  the 
hypochlorites. 


510  OUTLINES   OF  INDUSTRIAL   CHEMISTRY 

The  paper-making  process  is  chiefly  mechanical.  It  is  essential 
that  the  water  used  be  clear  and  colorless,  since  color  or  suspended 
matter  will  be  taken  up  by  the  pulp.  The  first  operation  is  "  fur- 
nishing" or  charging  the  hollander  with  the  stock;  the  kinds  and 
quantity  of  material  employed  depend  on  the  quality  of  the  paper  to 
be  produced.  Rag  stock  is  only  used  for  the  best  grades,  especially 
writing  papers.  New  linen  rags  and  waste  are  used  for  bond  paper, 
but  the  softer  writing  papers  are  made  from  old  rags.  The  quality 
of  paper  depends  largely  on  the  thorough  separation  of  the  fibres 
and  mixing  of  the  ingredients  in  the  hollander.  In  order  to  give 
the  paper  body,  weight,  and  greater  smoothness,  mineral  filler  or 
"loading"  material  is  employed.  This  must  be  exceedingly  fine, 
and  not  have  too  high  a  specific  gravity  or  solubility  in  water,  as 
its  retention  in  the  mat  of  the  fibre  would  be  thus  reduced.  It  must 
be  free  from  dirt,  grit,  and  mica,  since  these  cause  scratches  on  the 
polishing  rolls  or  spots  on  the  paper.  The  loading  is  done  in  the 
hollander  after  the  fibre  has  been  well  beaten  with  water.  The  filler 
is  thoroughly  mixed  with  the  pulp,  and  then,  for  engine  sized  paper, 
the  sizing  materials  are  added,  and  the  whole  beaten  until  a  perfect 
mixture  of  all  the  materials  is  obtained. 

Papers  intended  for  printing  or  writing  must  be  sized  or  coated 
on  the  surface  with  some  substance  which  will  prevent  the  absorp- 
tion and  consequent  spreading  of  the  ink.  For  liquid  writing  inks, 
the  sizing  must  be  more  perfect  than  for  the  viscid  printing  inks. 
Almost  the  only  sizing  materials  now  used  are  gelatine  "  animal  size," 
(used  on  the  better  grades  of  paper)  rosin,  and  casein.  These  are 
applied  in  several  ways.  Animal  size  is  applied  to  hand-made  papers 
by  dipping  each  sheet  separately  into  a  tub  of  the  glue  solution,  and 
allowing  it  to  dry  slowly.  The  operation  is  called  "tub  sizing." 
Machine-made  writing  paper  is  passed  in  continuous  web  through  a 
trough  filled  with  the  glue  solution.  It  is  then  cut  into  sheets,  and 
dried  very  slowly  by  hanging  it  in  a  loft  kept  at  an  even  tempera- 
ture ;  or,  in  cheaper  grades,  after  leaving  the  size  trough,  the  web 
passes  over  a  series  of  skeleton  driers,  within  which  fans  keep  up  a 
rapid  circulation  of  air.  Slow  drying  is  essential  to  animal  size,  in 
order  to  bring  it  to  the  surface.  Printing  papers  (except  some  kinds 
of  newspaper)  made  at  the  present  time  are  "engine  sized";  i.e.  a 
rosin  soap  (prepared  by  boiling  rosin  with  soda-ash)  is  added  in  the 
hollander,  and,  after  beating,  a  solution  of  aluminum  sulphate  is  intro- 
duced. The  alum  decomposes  the  rosin  soap,  forming  a  precipitate 
of  free  rosin,  and  perhaps  some  alumina  which  become  entangled  in 
the  openings  between  the  fibres.  When  the  paper  passes  between 


PAPER  511 

the  hot  calender  rolls  in  finishing,  this  rosin  is  fused  and  forms  a 
varnish-like  layer  on  the  surface.  The  aluminum  sulphate  should 
be  neutral  or  basic,  since  free  acid  decomposes  the  size  and  injures 
the  color  and  strength  of  the  paper.  For  good  results,  an  excess  of 
alum  over  the  amount  needed  to  decompose  the  rosin  soap  must  be 
used ;  and  the  precipitated  alumina  helps  to  hold  the  finer  parts  of 
the  fibre  and  filler  in  the  pulp  while  forming  the  sheet. 

Paper  is  usually  colored  by  adding  pigments  or  dyes  to  the  pulp 
in  the  hollander.  For  white  paper,  the  slight  yellow  tinge  of 
bleached  fibre  is  neutralized  with  a  trace  of  blue  or  pink,  ultra- 
marine or  coal-tar  dyes  being  used.  Some  pigments  are  precipitated 
on  the  fibre  by  adding  solutions  in  the  hollander ;  e.g.  potassium  bi- 
chromate and  lead  acetate. 

The  sheet  is  formed  in  three  different  ways :  by  the  hand  frame, 
by  the  cylinder  machine,  and  by  the  Fourdrinier  machine.  The 
hand  frame,  used  for  hand-made  paper,  is  simply  a  rectangular 
frame,  covered  with  wire  gauze,  and  having  a  slight,  removable  ledge 
around  the  sides.  This  frame  is  submerged  in  the  pulp,  mixed  to  a 
thin  cream  with  water ;  when  raised,  the  ledge  retains  some  of  the 
pulp  on  the  gauze,  while  the  water  drains  through ;  at  the  same  time 
the  workman  shakes  the  frame  slightly  from  side  to  side,  causing 
the  fibres  to  "  felt,"  and  forming  a  mat  of  pulp  on  the  gauze.  The 
frame  is  then  inverted  over  a  woollen  felt  blanket,  on  which  the  sheet 
of  pulp  drops.  A  number  of  these  pieces  of  felt,  each  carrying  a 
sheet  of  pulp,  are  piled  one  above  the  other,  and  heavily  pressed 
until  the  water  is  expelled.  The  sheets  are  then  "  tub-sized,"  as  above 
described.  The  final  finish  is  given  by  calendering  between  hot  rolls. 

The  cylinder  machine  is  essentially  the  same  as  that  described 
for  mechanical  pulp,  on  p.  502.  The  web  of  paper  pulp  is  carried 
on  an  endless  blanket  over  a  large  drying  cylinder,  and  then  lifted 
and  passed  between  heated  rolls.  The  paper  thus  made  is  weak, 
since  the  fibres  are  not  well  felted.  They  are  used  for  tissue  and 
blotting  papers,  and  are  not  sized. 

The  Fourdrinier  machine  is  very  complicated.  Essentially,  it  is 
as  follows :  —  An  endless  web  of  wire  gauze  is  supported  horizon- 
tally on  a  number  of  rollers,  and  travels  continually  in  one  direction. 
The  paper  pulp  flows  onto  this  from  a  storage  tank  called  the  "  stuff 
chest,"  the  thickness  of  the  sheet  being  regulated  by  the  supply  of 
pulp.  The  wire  gauze  is  given  a  continuous  sidewise  shaking  motion 
which  felts  the  pulp,  while  the  water  drains  away.  The  water  is 
drawn  away  by  the  action  of  "  suction  boxes  "  from  which  the  air 
can  be  partially  exhausted,  and  over  which  the  gauze  travels.  The 


512  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

web  is  next  transferred  to  an  endless  blanket  which  carries  it 
between  squeeze-rolls,  and  then  onto  a  second  felt,  where  it  is  again 
passed  between  rolls.  It  finally  passes  a  series  of  "couch  rolls," 
"  press  rolls,"  drying  cylinders,  and  calender  rolls  to  compact,  dry, 
and  polish  the  paper. 

By  fixing  a  slightly  raised  design  on  the  wire  gauze  of  the  hand 
frame  the  paper  is  made  slightly  thinner  along  the  lines  of  the  pat- 
tern, and  so-called  "water  marks"  are  made.  The  same  effect  is 
obtained  on  paper  made  on  the  Fourdrinier  machine  by  placing  a 
light  roller  ("dandy  roll")  carrying  the  design  in  relief,  between 
the  first  and  second  suction  boxes,  so  that  an  impression  is  made  on 
the  soft  pulp.  If  the  roll  is  covered  with  wire  gauze  the  impression 
of  the  weave  of  the  gauze  is  obtained,  producing  the  "  wove  "  papers. 
A  smooth  roll  carrying  ridges  forms  the  parallel  lines  on  "laid" 
paper.  By  using  a  roll  with  a  depressed  or  engraved  design  the 
paper  is  made  thicker  in  the  lines  of  the  pattern.  Imitation  water 
marks  are  often  made  by  pressing  the  finished  paper  with  plates 
carrying  the  design  in  relief,  or  by  slightly  parchmentizing  the  sur- 
face by  printing  with  certain  chemicals,  such  as  zinc  chloride  or 
sulphuric  acid. 

The  finishing  of  smooth  and  highly  sized  paper  is  done  by  calen- 
dering, or  passing  the  web  between  polished  rolls  of  chilled  iron, 
under  heavy  pressure.  A  higher  gloss  is  obtained  by  using  calen- 
ders with  rolls  made  of  heavily  pressed  paper,  alternating  with 
polished  iron  rolls.  Friction  calendering  consists  in  passing  the 
paper  between  a  pressed  paper  roll  running  at  high  speed,  and  an 
iron  roll  running  slowly.  For  very  high  gloss  the  paper  is  "  plated  " ; 
i.e.  passed  through  heavy  rolls  while  the  sheets  lie  between  polished 
zinc  plates. 

Printing  papers  are  usually  white,  and  often  contain  a  large  amount 
of  loading  material.  In  this  country  they  are  chiefly  made  from 
wood  pulp.  Some  kinds  are  heavily  calendered  to  secure  a  smooth 
surface.  Cheap  newspaper  is  largely  made  of  mechanical  pulp. 

Wrapping  papers  are  made  from  straw,  jute,  manilla  hemp,  old 
rope,  and  colored  rags.  The  stock  is  seldom  bleached,  and  hence 
is  very  often  deeply  colored.  Wrapping  papers  are  frequently 
calendered,  and  always  sized. 

Writing  papers  are  made  from  the  best  materials,  and  are  highly 
sized  and  carefully  calendered. 

Blotting  and  tissue  papers  are  unsized  and  unfilled,  the  former 
being  loosely  felted  and  thick ;  the  latter  is  made  from  long  fibres, 
especially  hemp  and  cotton,  and  is  the  thinnest  paper  made. 


PAPER  513 

Parchment  paper  is  made  by  dipping  unsized  paper  into  sulphuric 
acid,  diluted  with  one-fourth  its  volume  of  water,  to  which  a  little 
glycerine  is  added.  It  is  quickly  removed  and  washed  with  water, 
then  with  dilute  ammonia,  and  again  with  water.  The  acid  converts 
the  exterior  cellulose  of  the  fibres  into  amyloid,  which  coats  the 
fibres  and  cements  them  together,  forming  a  translucent  parchment- 
like  material  of  great  toughness.  The  action  of  strong  zinc  chloride 
solution  (sp.  gr.  1.82)  is  also  to  parchmentize  the  paper.  After 
washing,  the  paper  is  pressed  between  rolls,  dried,  and  sometimes 
calendered. 

Willisden  paper  is  made  by  passing  the  web  through  a  strong  solu- 
tion of  Schweitzer's  reagent  (copper  hydroxide  dissolved  in  strong 
ammonia  water),  and  pressing  together  several  sheets  so  prepared 
without  washing.  The  surface  of  the  cellulose  is  softened  and  made- 
sticky,  and  the  sheets  are  compacted  into  a  single  thick  one.  The 
evaporation  of  the  ammonia  leaves  the  cupro-cellulose  in  the  fibres, 
which  are  thus  coated  with  a  green  varnish-like  substance,  and  ren- 
dered waterproof. 

The  testing  of  paper  should  be  both  microscopical  and  chemical ; 
considerable  attention  is  given  to  this  on  the  continent  of  Europe, 
but  in  this  country  it  is  seldom  employed.  The  methods  and  details 
may  be  found  fully  described  in  Griffin  and  Little's  Chemistry  of 
Paper-Making,  Chap.  IX.,  and  in  the  works  'of  Wiesner  and  of 

Herzberg. 

REFERENCES 

Die  Fabrikation  des  Papiers.     L.  Miiller,  Berlin,  1877. 

The  Manufacture  of  Paper.     C.  T.  Davis,  Philadelphia,  1882. 

Guide  pratique  de  la  Fabrication  du  Papier.     A.  Proteaux,  Paris,  1884. 

Handbuch  der  Papierfabrikation.     S.  Mierzinski,  Wien,  1886. 

Die  Microscopische  Untersuchung  des  Papiers.     J.  Wiesner,  Leipzig,  1887. 

Die   Fabrikation   des  Papiers.     E.  Hoyer,  Braunschweig,  1887.     (Vieweg  o. 

Sohn. ) 
Die  Bestimmung  des  Holzschliffes  im  Papier.     A.  Mtiller,  Berlin,  1887.     (J. 

Springer.) 
The   Practical  Paper  Maker.     J.  Dunbar.     3d  Ed.     London,  1887.     (E.  and 

F.  N.  Spon.) 

Papier  Priifung.     W.  Herzberg,  Berlin,  1888.     (J.  Springer.) 
A  Textbook  of  Paper  Making.     C.  F.  Cross  and  E.  J.  Bevan,  London,  1888. 

(E.  and  F.  N.  Spon.) 
Le  Papier.    P.  Charpentier,  Paris,  1890.     (Tome  X.,  Encyclopedic  Chimique, 

par  M.  FrSmy.) 

The  Art  of  Paper  Making.     A.  Watt,  London,  1890. 

Technologie  der  Papier  Fabrikation.     Wurtemberg,  1893.     (Guntler-Straib.) 
The  Chemistry  of  Paper-Making.     R.  B.  Griffin  and  A.  D.  Little,  New  York, 

1894.     (Lockwood  &  Co.) 

2L 


514  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

A  Treatise  on  Paper-Making.     Carl  Hoffman,  New  York,  1895.     (Lockwood 

&Co.) 
Paper  Trade  Journal,  New  York,  1893,  June  24,  et  seq. :  — 

Evolution  of  the  Sulphite  Digester.     H.  A.  Rademacher. 
Journal  of  the  Society  of  Chemical  Industry  :  — 

1890,  Chemistry  of  Hypochlorite  Bleaching.    C.  F.  Cross  and  E.  J.  Sevan. 

1890,   9,  241,  Paper  Testing.     H.  Schlichter. 
United  States  Consular  Reports,  1894.     Parchment  Paper. 


LEATHER 

The  skin,  when  removed  from  the  animal,  very  soon  becomes 
putrid  if  kept  moist,  and  is  hard  and  horny  when  dried ;  in  either 
case,  boiling  water  converts  it  into  soluble  glue.  Leather  is  skin  so 
treated  that  it  remains  more  or  less  soft  and  pliable,  does  not  putrefy, 
and  is  not  readily  changed  into  glue.  Animal  skins  are  made  up  of 
three  layers,  —  the  epidermis,  the  fatty  tissues,  and  between  them 
the  corium,  cutis,  or  skin  proper.  The  epidermis  is  thin  and  the 
roots  of  the  hair  are  attached  to  it.  It  consists  of  individual  cells, 
which  become  dead  and  dry  on  the  outer  surface,  and  are  easily 
detached  by  friction  or  abrasion.  These  cells  are  largely  composed 
of  keratin,  a  substance  rich  in  sulphur,  and  very  little  affected  by 
cold  water ;  even  hot  water  does  not  produce  gelatine  from  it.  But 
the  young,  interior  cells  are  somewhat  attacked  by  lime-water.  The 
hair  and  keratin  substances  seem  to  be  dissolved  by  concentrated 
alkali  or  alkaline  sulphide  solutions.  The  fatty  tissues  form  the 
innermost  layer  of  the  skin,  and  consist  of  a  loose  network  of  con- 
nective tissue,  containing  fat  cells,  blood  vessels,  sudorific  glands, 
and  muscular  fibres.  The  ducts  of  the  sweat  glands  pass  through 
the  corium  and  epidermis. 

The  corium  or  dermis  is  the  only  part  of  the  skin  of  value  for 
leather;  it  consists  of  connective  tissue  composed  of  bundles  of 
fibres  which  interlace  somewhat  loosely  on  the  under  side  of  the 
skin,  but  are  closely  matted  on  the  epidermal  side.  This  fibrous 
substance  consists  chiefly  of  collagen,  which  appears  to  be  altered 
by  the  action  of  boiling  water  and  converted  into  soluble  gelatine 
or  glue.  Some  authorities  hold  that  an  intercellular  substance, 
coriin,  comparable  to  sericine  or  silk  glue,  p.  438,  fills  the  spaces 
between  the  bundles  of  fibres,  and  cements  them  together  when  the 
skin  dries,  making  the  skin  hard  and  stiff.  Other  writers  regard 
the  coriin  as  merely  an  alteration  or  decomposition  product  of 
collagen.  Both  collagen  and  coriin  are  bodies  of  an  albuminoid 


LEATHER  515 

character,  and  little  is  known  of  their  exact  chemical  composition. 
They  are  soluble  in  alkalies,  but  only  slowly  so  in  lime-water,  the 
coriin  being  the  more  readily  dissolved;  the  coriin  also  dissolves 
in  solutions  of  chlorides  of  the  alkalies  and  alkaline  earths. 

Pelts  are  divided  by  the  tanner,  according  to  their  size,  into  three 
general  classes:  —  (a)  hides,  comprising  the  skins  from  large  and 
fully  grown  animals,  such  as  the  cow,  ox,  horse,  buffalo,  walrus,  etc. ; 
these  form  thick  heavy  leather,  used  for  shoe  soles,  large  machinery 
belting,  trunks,  and  other  purposes  where  stiffness  and  strength, 
combined  with  great  wearing  properties,  are  essential ;  (6)  kips,  the 
skins  from  undersized  animals  or  yearlings  of  the  above  species; 
(c)  skins  obtained  from  small  animals,  such  as  calves,  sheep,  goats, 
dogs,  etc.  These  yield  lighter  leather  suitable  for  a  great  variety 
of  purposes.  The  thickest  and  heaviest  hides  come  from  rough, 
sparsely  settled  countries.  The  same  hide  varies  in  thickness  and 
texture  in  different  parts,  being  thicker  on  the  neck  and  butt  than 
on  the  flank  and  belly.  They  frequently  show  injury,  such  as  cuts, 
brand  marks,  and  holes  or  thin  places  caused  by  the  bot-fly  or 
warble.  Diseased  hides  are  often  sold,  which,  besides  yielding 
a  poor  leather,  are  a  source  of  danger  to  the  workmen,  owing  to  the 
contagious  nature  of  some  of  the  diseases  (especially  anthrax); 
hence  disinfectants  should  be  freely  used  in  the  tannery. 

Pelts  come  to  the  tanner  "  green  "  (fresh  from  the  animal),  salted 
(where  the  salt  has  been  thickly  rubbed  on  the  flesh  side),  or  dried. 
Green  pelts  are  usually  washed  in  clear  water  to  free  them  from 
blood  and  dirt;  salted  pelts,  if  not  dried,  are  merely  washed  in 
several  changes  of  water.  It  is  essential  to  remove  all  the  salt 
before  beginning  the  unhairing  process,  as  it  retards  the  action  of 
the  lime  and  interferes  with  the  "plumping"  of  the  skin.  It  is 
also  liable  to  cause  an  efflorescence  ("spueing")  on  the  finished 
leather.  Dried  hides  must  be  softened  by  soaking  them  in  luke- 
warm water  or  in  the  liquor  drawn  from  the  soaking  of  a  previous 
lot.  The  water  dissolves  part  of  the  hide  substance  and  putrefac- 
tion soon  begins  in  the  liquor,  developing  an  alkaline  reaction  owing 
to  the  formation  of  amines  and  ammonia,  and  giving  it  a  much  more 
rapid  softening  action  on  the  skin ;  but  great  care  is  necessary  in 
using  this  "putrid  soak,"  lest  the  decomposition  attack  the  hide 
fibre  itself.  Any  injurious  action  may  be  lessened  by  "handling," 
i.e.  drawing  the  skins  from  the  lower  part  of  the  pit  and  throwing 
them  back  on  top  of  the  heap.  Sometimes  careful  soaking  in  a 
warm,  very  dilute  sodium  sulphide  solution  is  substituted  for  the 


516  OUTLINES  OF  INDUSTRIAL  CHEMISTRY 

putrid  soak.  The  time  of  soaking  varies  from  two  or  three  days 
to  as  many  weeks,  depending  upon  the  thickness  and  dryness  of 
the  hide  and  the  age  and  temperature  of  the  "  soak  "  liquors.  When 
the  -hide  is  soft  enough  to  bend  in  a  short  turn  without  cracking,  it 
is  put  into  the  "  stocks,"  where  it  is  pounded  and  rolled  under  heavy 
wooden  mallets  and  rolls. 

The  character  of  the  water  used  in  the  tannery  is  important. 
Soft  water  makes  the  skins  thin  and  slim,  which  is  desirable  in 
light  leather.  Water  containing  calcium  or  magnesium  sulphate 
"  plumps  "  or  swells  the  hide,  thus  exposing  a  larger  surface  to  the 
action  of  the  tan  liquors,  which  is  desirable  for  heavy  hides. 
Chlorides  cause  the  hides  to  "  fall,"  i.e.  to  become  thin  and  flabby. 
This  may  be  due  to  the  greater  solubility  of  the  coriin  in  saline 
liquors.  If  used  for  washing  after  the  liming,  water  having  tempo- 
rary hardness  tends  to  fix  the  lime  among  the  fibres  in  an  insoluble 
form,  thus  causing  the  leather  to  be  harsh  on  the  grain  and  produc- 
ing colored  spots  because  of  unequal  deposits  of  tannin  and  coloring 
matters  in  the  tan  pits.  Hard  water  also  causes  waste  of  tannin 
matters  through  the  formation  of  insoluble  compounds  with  lime 
and  magnesia.  If  the  water  contains  organic  impurities,  it  may 
have  an  acid  nature  and  cause  the  hides  to  "fall"  after  liming,  or 
it  may  engender  putrefactive  changes  in  the  skin. 

When  thoroughly  cleaned  and  softened,  the  hides  undergo  the 
depilation  or  imhairing-  process.  This  removes  the  hair  and  epi- 
dermis, and  also  the  fatty  tissues  from  the  under  side  of  the  skin. 
It  is  done  in  several  ways :  —  by  treatment  with  an  alkaline  solu- 
tion which  attacks  and  softens  the  inner  layers  of  epidermal  cells, 
loosening  the  outer  layer  and  hair,  so  that  they  may  be  scraped 
away ;  or  by  "  sweating,"  in  which  the  young  epidermal  cells  are 
softened  by  putrefaction  until  the  outer  layers  are  loosened.  Lime 
is  the  most  common  unhairing  material,  sometimes  aided  by  the 
addition  of  sodium  sulphide,  arsenic  compounds,  or  calcium  hydro- 
sulphide. 

Liming.  —  The  skins  are  laid  in  a  vat  or  pit  with  milk  of  lime, 
which  loosens  the  epidermis  and  forms  a  soap  with  the  fatty  matter. 
It  also  dissolves  the  coriin,  loosening  the  fibres,  which  swell  and 
"  plump  "  the  hides.  It  is  used  in  excess  in  amounts  varying  from 
one-half  pound  for  a  small  light  skin  to  4  pounds  for  a  heavy  one. 
The  vats  or  pits  when  prepared  to  receive  the  skins,  are  called  "limes." 
The  skins  are  frequently  turned  over  and  worked  about  ("handled") ; 
for  heavy  hides  which  are  to  form  stiff,  hard  leather,  the  liming 
only  lasts  a  few  days ;  but  for  a  soft,  elastic,  pliable  product,  the 


LEATHER  517 

process  continues  for  15  or  20  days,  or  longer.  Warming  the  limes 
to  85°  or  90°  F.  hastens  the  action  very  much,  but  causes  the  skins 
to  "fall."  The  addition  of  sodium  sulphide  to  a  thick  cream  of 
lime  yields  a  paste  which  may  be  spread  on  the  hair  side  of  the 
skin,  and,  after  being  folded  together  for  a  few  hours,  the  hair  is 
easily  detached.  Arsenic  sulphides,  realgar  and  orpiment  (about 
10  per  cent  of  the  weight  of  the  lime),  are  frequently  added  to  the 
limes,  forming  calcium  sulph-arsenite  (HCaAsS3),  which  is  a  very 
rapid  depilatory. 

"  Sweating  "  is  much  used  for  hides  which  are  to  be  made  into 
sole  or  other  stiff  leather.  The  hides  are  hung  in  a  room  kept  at  a 
constant  temperature  of  18°  to  21°  C.,  the  atmosphere  being  saturated 
with  moisture.  Putrefaction  attacks  the  inner  layer  of  the  epider- 
mis, and  in  a  few  days  the  hair  is  loosened.  Before  treating  with 
tannin,  sweated  hides  must  be  "  plumped "  by  immersion  in  dilute 
acid. 

After  the  hair  has  been  loosened,  the  skin  is  laid  across  a  sloping 
"  beam  "  of  wood,  and  the  hair  and  epidermis  are  scraped  away  with  a 
blunt  knife.  The  fatty  tissues  are  removed  in  the  same  way,  but  a 
sharper  knife  is  used.  These  operations  are  known  as  "  beaming." 
After  trimming  off  the  waste  parts  of  the  skin,  it  is  thoroughly 
washed,  and  is  usually  again  scraped  on  the  "beam"  (scudded) 
to  remove  as  much  of  the  lime  as  possible.  All  these  operations 
described  above  are  carried  on  in  the  "  beam  house  "  of  the  tannery. 

If  soft,  pliable  leather  is  to  be  made,  the  skins  are  next  subjected 
to  the  "  bating,"  or  "  puering,"  process  to  destroy  the  "  plumping " 
produced  by  the  lime,  and  also  to  cause  other  changes,  the  nature 
of  which  is  rather  obscure.  Some  authorities  claim  that  the  bate 
merely  removes  the  lime  from  the  pores  of  the  hide,  while  others 
assert  that  it  also  takes  away  some  of  the  coriin,  thus  leaving  the 
fibres  looser,  and  allowing  more  perfect  action  of  the  tan  liquors. 
The  latter  view  seems  quite  probable,  and  there  is  little  doubt  that 
the  bacteria  in  the  bate  do  feed  upon  the  hide  substance.  Further, 
the  ferments,  tripepsin,  pancreatin,  etc.,  present,  undoubtedly  exer- 
cise some  function,  for  when  used  alone  they  will  cause  a  "plumped" 
skin  to  fall.  The  ammonium  salts  formed  doubtless  also  assist  in 
the  solution  of  the  lime  in  the  skin.  Bating  consists  in  soaking 
the  hides  in  a  mixture  of  dog  or  bird  dung  in  warm  water.  This 
quickly  becomes  putrid,  and  evolves  hydrogen  sulphide,  while  the 
liquor  acauires  an  alkaline  reaction.  The  process  lasts  from  2  to  4 
days,  according  to  the  thickness  of  the  skin  and  the  temperature. 
It  is  largely  dependent  upon  the  atmospheric  conditions;  in  the 


518  OUTLINES  OF  INDUSTRIAL   CHEMISTRY 

warm,  sultry  weather,  such,  as  usually  precedes  a  thunder-storm  in 
this  climate,  the  action  becomes  extremely  rapid,  and  a  few  hours  is 
often  sufficient  to  injure  the  skin.  Great  care  must  be  exercised  at 
all  times,  and  the  skins  stirred  about  frequently  to  prevent  too  great 
local  action,  resulting  in  thin  places  or  in  holes  in  the  leather. 

Many  proposals  have  been  made  to  replace  the  offensive  bate  with 
pure  solutions  of  weak  mineral  and  organic  acids ;  but  these  have 
not  generally  found  favor  with  tanners,  the  common  objection  being 
that  the  leather  is  made  harsh,  and  has  a  bad  grain. 

After  bating,  the  fibres  have  become  soft  and  pliable,  and  the 
whole  skin  has  a  smooth,  slippery  feel.  As  these  qualities  are  not 
desirable  in  sole  leather,  heavy  hides  are  not  bated. 

In  order  to  complete  the  removal  of  the  lime,  it  is  customary  to 
next  pass  the  skins  into  the  "bran  drench,"  consisting  of  an  infusion 
of  bran  and  water  at  a  temperature  of  about  32°  C.  On  standing, 
this  soon  develops  a  fermentation,  in  which  butyric  and  acetic  acids 
are  formed,  dissolving  the  lime. 

The  skins  are  now  ready  for  actual  conversion  into  leather,  or 
the  tanning  process.  This  is  done  in  three  ways :  - 

(1)  With  tannin  in  any  form  (vegetable  tannage). 

(2)  With  metallic  salts  (mineral  tannage). 

(3)  With  oils  or  fats  (oil  tannage). 

1.  The  sources  of  vegetable  tannins  have  been  considered  on 
p.  463.  For  leather,  it  has  been  found  essential  that  the  tannin 
material  shall  yield  other  extractive  matters  than  tannic  acid  when 
treated  with  water.  These  non-tannins  are  mainly  sugars,  gums, 
resins,  and  coloring  matters.*  They  assist  in  the  tanning  in  several 
ways,  —  some  of  them  are  directly  absorbed  by  the  skin,  increasing 
its  weight  and  solidity ;  others  set  up  fermentations  in  the  tan  pit, 
producing  organic  acids  which  assist  in  the  formation  of  a  leather  of 
a  good  body  and  weight.  The  tan  liquors  are  prepared  by  system- 
atic lixiviation  of  the  ground  tan-stuffs  in  pits,  the  strongest  liquors 
coining  in  contact  with  the  freshly  ground  material.  The  tempera- 
ture is  important,  warm  water  being  generally  best  for  complete 
extraction,  although  gambier  requires  cold  water.  The  spent  tan  is 
usually  burned  for  fuel.  Extracts,  alone  or  in  conjunction  with 
tan  liquors,  are  becoming  more  generally  used.  They  are  simply 
dissolved  in  water,  and  may  be  added  as  needed ;  but  they  are  often 

*  The  tannins  derived  from  gallic  acid  cause  a  white  efflorescence  (ellagic  acid) 
on  the  leather,  while  those  of  the  protocatechuic  acid  group  deposit  red  coloring  mat- 
ters (phlobaphenes)  in  it. 


LEATHER  519 

adulterated  with  glucose  or  molasses,  consequently  tests  with  the 
barkometer*  are  of  no  value  unless  the  material  is  known  to  be 
pure. 

Vegetable  tanning  is  used  for  sole  leather,  upper  leathers,  and 
colored  leathers  (morocco).  Sole  leather  is  heavy,  solid,  and  stiff, 
but  may  be  bent  without  cracking.  For  this,  tanning  materials 
such  as  oak  or  hemlock  bark,  mimosa,  chestnut  wood,  quebracho, 
valonia,  and  myrabolans  are  used.  The  hides  ("butts")  are  first 
hung  from  frames  in  pits  (suspenders),  containing  weak  or  nearly 
spent  tan  liquors  from  a  previous  lot.  Here  they  are  mechanically 
agitated,  so  that  they  take  up  the  tannin  evenly.  Strong  liquors 
would  so  harden  the  surface  as  to  prevent  thorough  penetration  into 
the  interior  of  the  hides.  This  partial  tanning  gives  the  skins  suffi- 
cient strength  to  withstand  the  rough  usage  which  they  receive 
when  transferred  to  the  handlers.  These  are  pits  in  which  the 
hides  lie  flat  in  a  pile,  which  is  worked  over,  or  "  handled,"  once  or 
twice  a  day  for  a  month  or  six  weeks.  There  are  several  of  these 
pits,  and  the  hides  are  treated  systematically,  first  with  weak  and 
then  with  stronger  liquors,  usually  strengthened  with  extracts. 
They  are  then  put  into  the  "layers."  These  are  pits  filled  with 
alternate  layers  of  hides  and  ground  bark,  valonia,  etc. ;  strong 
liquor  (ooze)  of  35°  barkometer  is  run  in  until  the  hides  are  sub- 
merged, and  the  pit  well  is  covered  with  ground  bark  to  exclude 
the  air.  After  8  or  10  days,  the  hides  are  taken  out,  rubbed  clean, 
and  "  laid  away  "  again  in  fresh  tan  and  stronger  liquor,  in  which 
they  remain  a  longer  time.  This  process  is  repeated  as  often  as 
necessary,  the  whole  time  consumed  being,  on  an  average,  from  8  to 
10  months.  It  may  be  hastened  by  keeping  the  liquor  in  the  tan 
pit  in  constant  circulation;  or  by  using  pressure  to  force  the  liquor 
into  the  skins;  or  by  using  very  strong  extracts,  and  continually 
moving  the  skins. 

Various  electrical  tannage  processes  have  been  devised,  in  which 
the  hides  are  suspended  in  strong  liquors,  and  kept  in  motion  while 
a  current  of  various  densities  and  voltage,  depending  upon  the  liquor, 
is  passed  through  the  solution.  This  is  claimed  to  hasten  the  pro- 
cess, but  the  product  has  been  criticised  as  lacking  substance  ("hun- 
gry "),  or  being  brittle.  This  is  true  of  most  rapid  tannages.' 

Sole  leather  is  usually  finished  by  brushing  and  washing,  followed 
by  slow  drying ;  the  drying  is  retarded  by  oiling  the  leather  several 
times  on  the  grain.  When  partly  dry,  it  is  "  sammed  "  by  piling  in 
a  heap  and  covering  until  heating  is  induced.  It  is  then  "  struck 

*  A  special  form  of  hydrometer  for  determining  the  strength  of  tan  liquors. 


520  OUTLINES  OF   INDUSTRIAL   CHEMISTRY 

out/7  i.e.  stretched  by  working  with  a  triangular  tool  having  blunt 
edges,  or  by  rolling  with  a  heavy  roller  under  pressure  in  a  machine. 
The  weight  of  the  leather  is  sometimes  increased  by  impregnating  it 
with  glucose,  or  with  barytes  or  other  mineral  salts.  Dry  hides 
yield  about  150  per  cent  of  their  weight  in  leather,  while  green 
hides  make  only  about  55  per  cent. 

Upper  or  dressed  leather  is  made  from  kips  and  large  calf  skins. 
After  bating,  the  skin  is  usually  shaved  on  the  flesh  side  to  make  it 
of  uniform  thickness.  It  is  then  tanned  and  the  grain  hardened  by 
handling  or  tumbling  in  revolving  boxes  or  drums,  in  a  rather  strong 
solution  of  tan  liquor,  usually  prepared  from  gambier.  The  tannage 
is  completed  with  mimosa,  myrabolans,  valonia,  or  bark,  the  liquors 
sometimes  being  heated  to  50°  or  60°  C.  After  a  final  tumbling  in 
sumach  liquor,  the  leather  is  finished  by  currying.  That  is,  it  is 
first  scoured  with  brushes  and  then  rubbed  with  a  "  sleeker,"  a 
smooth  stone  or  piece  of  glass  which  removes  the  creases  and 
wrinkles  and  stretches  the  leather.  It  is  then  "stuffed"  with  a 
mixture  of  oil,  soap,  and  tallow  which  is  worked  into  it  by  rolling 
or  tumbling  in  a  drum.  Olive,  neat's-foot,  sperm,  and  fish  oils  are 
much  used  for  this,  as  is  also  degras  (p.  523).  Upper  leathers  are 
usually  blacked  by  rubbing  with  a  mixture  of  lampblack  and  oil  or 
tallow ;  or  they  may  be  painted  with  a  solution  of  copperas  and  log- 
wood. 

Colored  leather  is  made  chiefly  from  goat,  sheep,  and  calf  skins. 
These  are  limed,  unhaired,  bated,  and  drenched  as  above  described, 
and  are  tanned  with  gambier  or  sumach  liquors,  in  tumblers  or 
drums,  or  in  tubs,  or  handlers  where  they  are  kept  in  motion. 

Colored  leathers  are  usually  dyed  with  basic  dyestuffs  or  with 
natural  dyewood  extracts,  particularly  logwood.  After  tanning, 
they  are  passed  into  a  bath  of  tartar  emetic  to  fix  the  tannin  before 
dyeing.  The  dyeing  is  done  in  slightly  warm  baths,  as  hot  liquors 
are  injurious.  The  skin  is  folded  down  the  middle  with  the  grain 
side  out,  and  is  then  laid  in  a  slightly  warm  solution  of  the  dye  in 
a  shallow  tray ;  or  the  skin  may  be  sponged  with  the  dye  on  the 
grain  side  while  spread  on  a  table.  If  it  is  to  be  dyed  through,  it  is 
worked  with  the  dye  solution  in  a  tumbler  or  paddle-wheel. 

After  bating  or  when  partially  tanned,  the  skins  are  usually  split 
into  two  or  three  layers,  by  a  sharp  knife  driven  by  machinery. 
The  grain  side  is  finished  to  form  "  skivers,"  while  the  flesh  side  is 
made  into  patent  leather,  wash  leather  (chamois),  or  into  cheap 
leather  with  an  artificial  grain.  The  very  thin  grain  splits  from 
sheep  and  calf  leather  are  used  for  book  bindings.  The  flesh  splits 


c« 


LEATHER  521 

are  often  given  an  artificial  grain  ("pebbled"),  by  rolling  with  an 
engraved  roll,  or  with  a  die  under  heavy  pressure.  This  imitation 
may  be  carried  so  far  as  to  make  small  punctures  in  the  leather 
with  fine  pin  points  to  resemble  the  pores  and  hair  sheaths  of  the 
natural  grain.  Or  an  electrotype  may  be  made  from  a  piece  of 
natural  leather,  and  this  copy  fixed  on  the  die. 

2.  Tanning  with  metallic  salts  or  tawing  is  employed  for  small 
skins  and  light  leathers,  and  has  recently  become  very  important  in 
this  country;  the  salts  used  are  certain  aluminum,  chromium,  and 
iron  compounds,  especially  sulphates,  chlorides,  and  bichromates. 
Alum  (or  aluminum  sulphate)  is  much  employed  (always  in  conjunc- 
tion with  common  salt)  for  white  and  kid  leathers.  After  liming, 
usually  with  the  addition  of  arsenic,  for  three  or  four  weeks,  and 
unhairing  and  fleshing,  the  skins  are  very  thoroughly  bated,  drenched, 
and  scudded.  For  white  leather,  the  split  skins  are  tumbled  in  a 
drum  with  a  solution  of  alum  and  salt,  and  after  lying  folded  several 
hours  are  dried  without  washing.  The  hard  skin  is  then  softened 
by  pounding,  rolling,  and  stretching.  Kid  leather  for  gloves,  and 
calf  kid  are  made  by  tumbling  or  treading  the  split  skins  in  a  mixt- 
ure of  alum,  salt,  flour,  egg-yolk,  and  olive  oil,  until  they  are  thor- 
oughly impregnated,  and  then  drying.  The  leather  is  colored  with 
natural  or  coal-tar  dyes,  and  is  usually  again  tumbled  in  the  salt  and 
egg-yolk  emulsion.  It  is  softened  by  "  staking,"  i.e.  pulling  across 
the  edge  of  a  blunt  knife  fixed  in  a  vertical  position  in  a  post.  The 
flesh  side  is  shaved,  and  the  grain  glazed  or  polished  carefully  by 
rubbing  with  a  sleeker,  or  in  a  glazing  machine. 

Very  excellent  leather  is  produced  by  combining  the  alum  tan- 
ning process  with  tannage  in  gambier  liquor,  the  method  being 
known  as  the  combination  tannage,  or  dongola  process.  This  is  much 
used  for  making  leather  resembling  kid,  but  stronger  and  cheaper, 
which  is  largely  used  for  ladies'  shoes.  The  prepared  skins  are 
tawed  in  alum  and  salt  and  then  laid  in  gambier  liquor  for  several 
days  or  a  week. 

Chrome  tannage,  or  tawing  with  chromium  salts,  has  been  chiefly 
developed  in  this  country  and  is  now  in  general  use  here.  The  prin- 
ciple of  the  process  consists  in  precipitating  an  insoluble  chromium 
hydroxide  or  oxide  on  the  fibres  of  a  skin  which  has  been  impreg- 
nated with  a  soluble  chromium  salt,  usually  potassium  bichromate; 
basic  chromium  chloride,  chromium  chromate,  and  chrome  alum  are 
also  used.  The  skins,  having  been  limed,  unhaired,  fleshed,  bated, 
drenched,  and  scudded,  are  worked  in  a  solution  of  potassium  bi- 


522  OUTLINES   OF   INDUSTRIAL  CHEMISTRY 

chromate  to  which  some  common  salt  has  been  added,  together  with 
one-fourth  to  three-fourths  of  the  theoretical  amount  of  hydrochloric 
or  sulphuric  acid  necessary  to  liberate  all  the  chromic  acid  (Cr08). 
After  several  hours,  when  the  skin  shows  a  uniform  yellow  color 
when  cut  through  the  thickest  part,  it  is  removed,  the  excess  of  water 
pressed  out  or  drained  away,  and  the  skin  worked  in  a  bath  of  sodium 
bisulphite  (NaHS03),  or  thiosulphate,  to  which  has  been  added  some 
mineral  acid  to  liberate  the  sulphur  dioxide :  — 

1)  K20207  +  2  HC1  =  2  KC1  +  H20  +  2  Cr03. 

2)  Na2S203  +  2  HC1  =  2  NaCl  +  H20  +  S  +  S02. 

3)  2  Cr03  +  3  S02  +  3  H20  =  3  H2S04  +  Cr203. 

The  chromic  acid  is  absorbed  by  the  fibre  and  is  later  reduced  in  situ 
by  the  sulphurous  acid.  It  is  necessary  to  use  a  strong  solution  of 
the  reducing  agent,  so  that  the  reduction  may  be  fully  accomplished 
before  the  chromic  acid  has  time  to  "bleed"  from  the  skin.  The 
strength  of  solutions  recommended  vary  somewhat  in  the  various 
processes,  but  are  usually  made  from  10  to  30  grams  per  litre-  for  the 
bichromate,  and  30  to  50  grams  for  sodium  thiosulphate.  Calculated 
on  the  weight  of  the  skin,  from  4  to  9  per  cent  of  bichromate,  and 
about  15  per  cent  thiosulphate  are  usually  employed.  The  amount 
of  chromic  acid  fixed  on  the  fibre  is  about  4  to  6  per  cent,  calculated 
as  bichromate,  K2O207. 

Chrome  leather  is  tough  and  resists  moisture  very  thoroughly. 
On  this  latter  account,  skins  which  are  to  be  dyed  should  be  intro- 
duced into  the  dye  at  once  after  reducing  and  washing,  for  if  allowed 
to  dry,  the  dyeing  is  incomplete.  The  leather  may  be  heated  to 
80°  C.  or  more  without  injury,  and  hence  can  be  dyed  with  some  of 
the  alizarin  colors.  It  is  a  very  rapid  process,  the  time  of  steeping 
in  the  chrome  bath  being  only  a  few  hours  and  even  less  in  the  re- 
ducing bath.  It  is  a  very  light  tannage,  and  on  thick  skins  has  con- 
siderable tendency  to  contract  the  fibre,  and  so  is  not  used  for  sole  or 
upper  leathers.  It  is  chiefly  employed  for  glazed  kid,  calf  kid,  and 
glove  leathers.  The  tanned  or  colored  skins  are  oiled  and  stuffed 
before  drying. 

Chrome  processes  have  been  covered  with  patents,  and  consider- 
able litigation  is  now  going  on  in  this  country  concerning  them. 

Tawing  with  iron  salts  has  been  the  subject  of  several  patents, 
but  these  processes  are  little  used. 

3.  Tanning  with  oils  consists  in  saturating  the  flesh  side  of  split 
skins  with  oils  (whale  or  cod  liver),  and  allowing-  them  to  lie  in 


.      LEATHER  523 

heaps  until  an  oxidation  or  fermentation  of  the  oil  ensues.  The 
mass  heats,  and  a  soft  spongy  leather,  such  as  chamois  and  buff 
leather,  is  formed.  The  skin  being  Mmed,  bated,  and  drenched, 
excess  of  water  is  removed  by  pressing,  and  the  skin  is  worked  in 
the  stocks  with  oil.  After  partial  drying  it  is  again  stocked  with 
oil;  this  is  continued  until  all  the  moisture  in  the  skin  has  been 
replaced  by  oil.  After  partial  oxidation  the  excess  grease  is  removed 
by  pressing,  or  in  the  centrifugal  machine.  The  thick,  greasy  mass 
expressed,  called  "degras,"  consists  of  semioxidized  oil,  and  is  a 
valuable  currying  agent.  The  skins  are  now  washed  in  a  bath  of 
soda  or  potash  to  remove  the  rest  of  the  grease.  These  alkaline  wash- 
waters  are  treated  with  mineral  acid,  decomposing  the  soaps,  and 
setting  free  the  fatty  acids  which  rise,  and  are  skimmed  off  as 
"  sod-oil,"  also  used  in  currying.  These  oils  have  undergone  a  pecul- 
iar change  in  which  oxy-acids  are  formed  which  unite  with  the 
hide  fibre,  similarly  to  the  combination  of  tannic  acid,  and  washing 
with  soap  or  alkali  is  not  sufficient  to  remove  the  combined  fat; 
but  the  uncombined  fat  is  washed  away  completely. 

The  oil-tanned  skins  are  finally  stretched,  scraped,  and  bleached 
in  the  sun,  or  in  sulphur  dioxide.  Chamois  leather  is  often  further 
softened  by  freezing  while  wet. 

Morocco  leather  is  made  from  goat  skins  tanned  with  sumach, 
which  gives  a  very  light-colored  product.  The  prepared  skins  are 
tanned  by  paddling  in  sumach  liquor ;  or  they  are  sewed  up  to  form 
bags  which  are  filled  with  the  liquor,  and  then  piled  in  a  tank  where 
the  pressure  of  one  bag  upon  the  other  forces  the  liquor  through 
the  skins.  The  so-called  French  morocco  is  made  from  sheep  skins, 
either  whole  ("roans"),  or  split  ("skivers").  These  leathers  are 
usually  dyed  in  colors,  two  skins  being  placed  with  their  flesh  sides 
together,  and  brushed  over  with  the  color,  or  immersed  in  a  tray  or 
drum  filled  with  the  dye  liquor.  To  imitate  the  grain  of  goat  skin, 
French  calf  is  usually  "grained"  by  rolling  under  a  cork-surfaced 
board. 

Russia  leather  was  formerly  tanned  with  willow  bark,  but  oak 
bark  is  now  much  used,  especially  for  imitations.  The  peculiar  odor 
is  due  to  an  oil  obtained  by  distilling  birch  bark,  and  used  for  curry- 
ing the  leather.  The  dull  red  color  is  produced  by  dyeing  with  red 
wood  (Brazil  or  saunders-wood). 

Patent  leather  is  made  by  coating  a  tightly  stretched  split  skin,  or 
"  skiver,"  with  a  varnish  of  linseed  oil,  containing  lampblack,  Prus- 
sian blue,  or  other  pigment.  While  the  leather  is  still  stretched  the 


524  OUTLINES  OF  INDUSTRIAL  .CHEMISTRY 

varnish  is  dried  at  70°  C.,  and  the  surface  is  smoothed  with  fine 
pumice,  and  other  coats  of  varnish  laid  on  and  dried.  The  final  coat 
is  polished  with  tripoli,  or  rotten  stone 

Parchment  and  vellum  are  made  from  untanned  split  skins.  The 
former  is  made  by  stretching  wet  sheep  skin,  after  liming  and  flesh- 
ing, 011  a  frame,  and  drawing  it  smooth  and  free  from  wrinkles. 
Powdered  chalk  is  dusted  over  it,  or  mixed  with  water  and  painted 
on  the  skin  to  absorb  the  grease,  and  the  surface  is  then  smoothed 
by  rubbing  with  pumice.  After  scraping  with  a  steel  blade  and  a 
final  smoothing,  the  skin  is  slowly  dried  in  a  shady  place.  Vellum  is 
made  from  calfskin,  only  those  of  uniform  color  being  used.  The 
liming  lasts  for  three  or  four  weeks,  and  the  washing  is  very  thor- 
ough. The  skin  is  then  split  and  stretched  on  a  frame,  and  dried 
with  scraping  and  pumicing  as  in  the  case  of  parchment. 

Artificial  leather  is  made  from  paper  and  certain  cellulose  deriva- 
tives ("  viscoid ").  or  from  various  kinds  of  fibrous  materials  coated 
with  gelatine  and  heavily  compressed.  Sometimes  leather  scraps 
and  trimmings  are  ground  to  shreds  and  soaked  in  gum  or  gelatine, 
and  formed  into  boards  by  heavy  pressure.  These  leatherettes  are 
chiefly  used  for  embossed  trimmings  in  book  binding,  and  in  places 
where  pliability  is  not  essential. 

Degras  is  now  so  important  as  a  currying  agent  that  it  is  manu- 
factured on  an  extensive  scale.  The  wash  leather  produced  is  again 
saturated  with  oil,  and  the  oxidized  oil  pressed  out ;  the  process  is 
repeated  an  indefinite  number  of  times,  as  long  as  the  skin  holds 
together. 

The  exact  nature  of  tanning  is  not  understood,  but  two  theories 
are  advanced  by  authorities.  The  physical  theory  admits  no  chemi- 
cal combination  between  the  tan-stuff  and  the  hide  fibre,  holding 
that  the  latter  is  merely  coated  with  the  tan-stuff,  and  the  individual 
fibres  being  thus  prevented  from  adhering  to  each  other  on  drying 
the  leather  remains  soft  and  pliable.  The  chemical  theory  assumes 
a  true  chemical  combination  to  exist  between  the  tan-stuff  and  the 
hide  substance.  With  tannic  acid  and  tannins,  at  least,  there  does 
appear  to  be  a  chemical  union,  and  this  may  also  be  true  of  chromium 
salts.  But  with  alum,  which  may  be  entirely  removed  from  the 
leather  by  hot  water,  the  combination  certainly  does  not  seem  to  be 
complete.  With  oil  tannage  the  grease  appears  to  decompose  within 
the  hide  substance  and  become  fixed  on  the  fibre  by  oxidation,  but 
without  true  combination,  the  process  being  analogous  to  the  dyeing 
with  reduced  indigo,  p.  490. 


GLUE  525 


REFERENCES 

Grundziige  der  Lederbereitung.    C.  Heinzerling,  Braunschweig,  1882.    (Vieweg.) 
The  Manufacture  of  Leather.     C.  T.  Davis,  Philadelphia,  1885.     (Baird  &  Co.) 
Text-book  of  Tanning.     H.  R.  Proctor,  London,  1885.     (E.  and  F.  N.  Spon.) 
Traite"  pratique  de  la  Fabrication  des  Cuirs,  etc.    A.  M.  Villon,  Paris,  1889. 

(Baudry  et  Cie.) 

The  Art  of  Leather  Manufacture.    A.  Watt.     3d  Ed.     London,  1890.     (Lock- 
wood.) 

Die  Lohgerberei.     F.  Wiener.     2te  Auf.     Leipzig,  1890. 
Leather  Manufacture.     J.  W.  Stevens,  London,  1891. 
Praktisches  Lehrbuch  der  Lohgerberei.     S.  Kas,  Weimar,  1891.     (Voigt.) 
Industrie  des  Cuirs  et  des  Peaux.     T.  Jean,  Paris,  1892. 
Cuirs  et  Peaux.     H.  Voinesson  de  Lavelines,  Paris,  1894.     (Balliere  et  Fils.) 
Die  Herstellung  der  lohgaren  Leder.     L.  Hoffmanns,  Weimar,  1893.     (Voigt.) 


GLUE 

Glue  is  a  decomposition  product  from  animal  connective  and 
elastic  tissues.*  When  heated  with  water,  these  tissues  lose  their 
peculiar  structure,  swell,  and  finally  dissolve,  forming  a  non-adhesive 
solution.  On  cooling,  this  jellies  and  dries  into  a  horny,  translucent 
mass,  which  is  the  glue.  When  redissolved  in  hot  water,  this  forms 
a  thick  solution  having  strong  adhesive  properties.  Gelatine  is  made 
more  carefully,  from  better  stock,  but  chemically  there  is  no  differ- 
ence between  it  and  glue.  Both  swell  with  cold  water,  but  do  not 
go  into  solution  until  the  water  is  heated. 

Commercial  glue  from  any  source  contains  two  essential  constitu- 
ents,—  glutin,  an  amorphous,  odorless,  tasteless  protein  substance, 
soluble  in  hot  water,  having  great  adhesive  strength,  and  precipitated 
from  solution  by  tannin  or  alcohol ;  and  chondrin,  similar  to  glutin, 
but  mainly  derived  from  the  cartilaginous  and  young  bone  tissues, 
and  having  less  adhesive  strength.  There  are  three  general  classes, 
hide  glue,  bone  glue,  and  fish  glue.  Hide  glue  is  made  from  glue 
stock,  i.e.  waste  bits  of  hide  trimmings,  skivings,  fleshings,  and  other 
untanned  refuse  from  the  beam  house ;  slaughter-house  waste,  such 
as  the  ear-laps  and  heads  (petes),  sinews,  feet,  and  tails  of  cattle  and 
sheep ;  and  the  skins  of  rabbits,  hares,  and  dogs,  and  scraps  of  alum 
tawed  leather.  Tanned  skins  are  of  no  use  for  glue-making. 

The  stock,  wet,  or  dried  and  salted,  is  washed,  and  then  limed  for 
from' six  weeks  to  several  months,  during  which  time  it  is  thoroughly 
and  frequently  stirred.  It  swells,  and  the  fats  are  converted  into 
*  Ost,  Lehrbuch  der  technischen  Chemie,  p.  591. 


526  OUTLINES   OF  INDUSTRIAL   CHEMISTRY 

lime  soap,  while  blood,  flesh,  and  coriin  are  partly  dissolved.  The 
stock  is  then  thoroughly  washed  in  tubs,  with  mechanical  stirrers,  or 
rollers,  to  remove  the  lime,  lime  soap,  and  dirt;  the  last  trace  of  lime 
is  removed  by  treating  with  dilute  hydrochloric  acid,  or,  better,  with 
sulphurous  acid,  which  both  plumps  and  bleaches  the  stock.  The 
excess  acid  is  washed  away,  and  the  stock  is  ready  for  "  cooking  "  or 
"  boiling,"  to  convert  the  collagen  into  glue.  The  temperature  of 
heating  is  from  65°  to  100°  C.,  although  actual  boiling  of  the  liquor 
is  avoided.  The  kettles  are  open  wooden  vats,*  heated  by  closed 
steam  coils,  above  which  is  a  perforated  false  bottom ;  above  this  is 
a  grating,  then  a  layer  of  excelsior  or  straw,  and  finally  an  iron 
grating,  upon  which  the  glue  stock  rests.  Water  is  added,  and  the 
contents  of  the  kettle  is  heated  until  the  stock  dissolves,  forming  a 
solution  thick  enough  to  jelly  on  cooling.  Long  cooking  of  the 
solution  must  be  avoided,  or  considerable  decomposition  occurs,  and 
the  strength  of  the  product  is  decreased.  The  grease  and  lime 
soaps  rise,  and  are  skimmed  off;  the  solid  matter,  consisting  of 
hair,  etc.,  sinks,  and,  together  with  the  excelsior,  forms  a  filter 
through  which  the  liquor  is  slowly  drawn  off  from  under  the  false 
bottom,  and  a  clear  solution  is  obtained ;  or  the  liquor  may  be  fil- 
tered on  felt  or  in  bag  filters. 

The  stock  is  not  all  dissolved  in  the  first  liquor,  and  usually  from 
three  to  five  boilings  with  fresh  water  are  necessary  to  extract  all  the 
glue ;  these  later  solutions  are  thicker  and  stronger,  consequently  all 
the  liquors  are  usually  mixed  together,  except  the  first,  which  yields 
the  finest  product.  Preservative  agents,  such  as  zinc  sulphate 
(p.  240),  alum,  borax,  salicylic  acid,  formalin,  etc.,  are  added  to  the 
liquor.  Alum  is  said  to  injure  the  adhesive  strength. 

Sometimes  the  stock  is  treated  in  closed  kettles  with  direct  steam 
under  pressure,  thus  causing  rapid  melting. 

If  the  liquor  is  too  thin  to  jelly,  it  is  concentrated  in  a  vacuum 
pan;  or  it  maybe  boiled  down  in  an  open  kettle,  coagulating  the 
albuminous  matter,  which  is  removed  by  skimming;  a  clear  glue  is 
thus  obtained,  but  its  strength  is  lessened.  The  solution  is  then  run 
into  coolers,  which  differ  in  size  and  shape.  A  good  form  is  a  gal- 
vanized iron  pan  13  inches  long  by  11  inches  wide  by  9  inches  de_ep, 
and  having  slightly  flaring  sides.  This  is  cooled  by  standing  in 
cold  water,  or  by  the  use  of  refrigerating  machines. 

In  from  12  to  24  hours  the  solution  jellies,  forming  a  mass 
containing  about  85  per  cent  water.  This  is  turned  out  on  a  table 
and  cut  into  plates  from  one-eighth  to  one-fourth  of  an  inch  thick, 
*  Tinned  metal  kettles  are  sometimes  used  instead  of  wooden  vats. 


GLUE  527 

by  means  of  wires  stretched  tightly  across  a  frame.  These  slices 
must  be  carefully  dried  at  once ;  they  are  put  in  single  layers  on 
wire  frames  and  passed  into  the  dry-room,  a  long,  narrow  room  from 
which  sunlight  is  excluded,  and  which  is  heated  by  hot  air,  blown 
in  at  the  end  farthest  from  where  the  glue  enters.  The  jelly  is  very 
apt  to  develop  mould  or  to  liquefy  through  the  action  of  bacteria, 
while  if  the  temperature  rises  over  35°  to  40°  C.,  it  is  liable  to  melt, 
forming  a  "daub."  But  in  clear,  cold  weather,  the  temperature  may 
rise  to  43°  C.  In  summer  it  is  nearly  impossible  to  dry  the  films 
properly  and  no  glue  is  made.  If  the  wet  film  is  frozen,  the  glue 
is  very  spongy  and  porous  when  dry.  The  glue  should  dry  in  about 
24  hours,  when  the  trays  are  removed  from  the  hot  end  of  the  dry- 
ing-room and  the  films  broken  or  ground  in  a  disintegrator  mill  and 
packed  for  shipment.  The  dry  glue  contains  about  15  per  cent 
water. 

Bone  glue  is  not  essentially  different  from  hide  glue,  and  is  made 
from  green  bones  which,  for  the  better  qualities,  must  be  quite 
fresh.  They  are  boiled  with  water,  and  the  oily  matter  skimmed 
off  as  it  rises ;  or  better,  the  bones  are  extracted  with  benzine  or 
other  solvent,  in  a  "  rendering  tank,"  p.  306.  The  extracted  bones 
are  crushed  and  treated  with  dilute  hydrochloric  acid  (sp.  gr.  1.05) 
until  the  calcium  phosphate  and  other  salts  are  dissolved.  The 
cartilaginous  residue  is  then  treated  with  lime-water  to  remove  any 
acid.  After  washing,  the  mass  is  boiled  with  water  or  steamed  in 
a  digester  until  dissolved.  Any  grease  is  skimmed  or  filtered  off 
and  the  gelatine  is  chilled  and  dried  as  already  described.  Benzine 
extracted  bones  are  often  crushed  and  boiled  directly  or  steamed  for 
glue.  The  glue  solution  is  then  strained  through  a  cloth,  bleached 
by  treatment  with  sulphurous  acid,  and  evaporated  at  about  60°  C. 
in  vacuo,  or  in  open  troughs  with  a  rotary  steam-coil  half  sub- 
merged in  the  liquid.  The  thick  solution  is  then  chilled,  jellied, 
and  dried  as  above. 

Fish  glue  is  made  by  boiling  the  heads,  fins,  and  tails  of  fish 
at  110°  C.  It  has  very  weak  jellying  properties  and  is  generally 
made  into  liquid  glue,  the  disagreeable  odor  being  destroyed  by 
adding  creosote,  oil  of  sassafras,  or  other  strong-smelling  substance. 

Liquid  glue  is  made  by  treating  fish  or  common  glue  with  acetic, 
nitric,  or  hydrochloric  acid,  whereby  the  property  of  gelatinizing 
when  cold  is  lost.  But  the  adhesiveness  is  not  materially  changed ; 
and  since  such  glues  do  not  require  to  be  heated  or  applied  to  hot 
surfaces,  they  are  extensively  used. 

Gelatine  is  prepared  from  calf  or  sheep  skin  and  from  sturgeon 


528  OUTLINES  OF  INDUSTRIAL   CHEMISTRY 

and  other  fish  skin.  The  first  liquors  formed  in  the  boiling  or 
steaming  yield  a  colorless  gelatine  which  is  used  for  food  and  in 
the  preparation  of  photographic  emulsions.  The  solution  is  often 
filtered  on  bone-black  or  bleached  with  sulphur  dioxide  before  jelly- 
ing. Much  is  used  in  clarifying  liquors  containing  tannins,  espe- 
cially wines,  etc. 

Isinglass  is  a  pure  white,  odorless,  tasteless  gelatine,  prepared 
from  the  inner  skins  of  the  swimming  bladders  of  fish.  It  is  almost 
entirely  soluble  in  water  at  about  50°  C.,  and  forms  a  transparent 
jelly  on  cooling.  Owing  to  its  high  price  and  slight,  adhesive 
strength,  it  is  used  only  for  food  and  in  clarifying  liquors,  such  as 
wine,  beer,  coffee,  etc. 

A  vegetable  gelatine  derived  from  a  species  of  algae  or  seaweed 
forms  the  agar-agar,  p.  351,  or  Bengal  isinglass  of  commerce. 

Satisfactory  methods  for  glue  testing  have  not  yet  been  devised. 
The  usual  tests  are  determinations  of  the  viscosity  and  firmness 
of  the  jelly  formed,  but  the  adhesiveness  does  not  depend  upon  the 
quality  of  the  jelly.  Glue  is  usually  sold  according  to  its  color  and 
physical  properties,  and  should  be  free  from  grease. 

REFERENCES 

Die  Fabrikation  chemischen  Products  aus  thierischen  Abfallen.     H.  Fleck, 

Braunschweig,  1878. 

Die  Leim  und  Gelatin  Fabrikation.    2"  Auf.    F.  Dawidowsky,  Wien,  1879. 
Glue  and  Gelatine.     Dawidowsky-Brannt,  Philadelphia,  1884.     (Baird  &  Co.) 
Cements,  Pastes,  Glues,  and  Gums.     H.  C.  Standage,  London,  1893. 


INDEX 


Abraumsalze,  132. 

Absinthe,  412. 

Absorption  machines  for  refrigeration, 

20. 
Acetate  of  aluminum,  262. 

of  calcium,  262. 

of  calcium,  brown  and  gray,  259. 

of  chromium,  262. 

of  copper,  263. 

of  iron,  263. 

of  lead,  263. 

of  sodium,  263. 
Acetone,  260. 
Acetylene  gas,  277. 
Acid,  acetic,  261,  462. 

acetic,  glacial,  261. 

"  chamber,"  45. 

citric,  463. 

hydrochloric,  67. 

hyposulphurous,  44. 

lactic,  415,  463. 

muriatic,  67. 

nitric,  114. 

nitrosylsulphuric,  46,  47. 

oleic,  330. 

oxalic,  as  assistant  in  dyeing,  462. 

palmitic,  330. 

pyroligneous,  257. 

stearic,  330. 

sulphuric,  45. 

sulphuric,  fuming,  45. 

tannic,  463. 

tartaric,  as  assistant  in  dyeing,  463. 
Acid  dyes,  484. 
"Acid  egg,"  55. 
Acridine  dyes,  477, 
Acrolein,  303. 
Agar  agar,  351,  528. 
Agitator  for  petroleum  refining,  293. 
Air  gas,  277. 
Air-lift  pump,  56. 
Alcohol,  405. 

methyl,  259. 
Ale,  404. 

2M 


Alizarin,  468,  478. 

Alkaline  process  for  corn  starch,  354. 

Alkaline  water,  35. 

Alum,  244. 

"  Alum  meal,"  245. 

Alum  shales  as  source  of  alum,  245. 

"  Alumino-ferric  cake,"  241. 

Aluminum  acetate,  262. 

sulphate,  240. 

sulphate  from  bauxite,  241. 

sulphate  from  clay,  241. 

sulphate  from  cryolite,  243. 
Aluminum  mordants,  458. 
Al unite  as  source  of  alum,  244. 
Amber,  342. 
Amberite,  431. 
American  vermilion,  210. 
Amide  powder,  422. 
Amidoazo  dyes,  474. 

sulphonic  acids,  475. 
Ammonia,  124. 

soda  process,  86. 
Ammoniacum,  350. 
Ammonite,  432. 
Ammonium  jdum,  246. 

carbonate,  129. 

chloride,  129. 

nitrate,  122. 

sulphate,  128. 

sulphocyanide,  248. 
Amorphous  phosphorus,  223. 
Amylodextrin,  354. 
Amyloid,  435. 
Analyzer,  9. 
Aniline  black,  473,  491. 

dyes,  471. 
Annatto,  470. 

Annealing  furnace  for  glass,  173. 
Anthracene  colors,  477. 

oil,  284. 
Anthracite,  26. 
Antimony  orange,  208. 

red,  212. 

salts  as  mordants,  461. 
"Anti-scale"  preparations,  38. 
Apatite,  140. 


529 


530 


INDEX 


Archil,  469. 
Argol,  391. 
Arrack,  411. 
Arrowroot,  361. 
Arsenic  acid,  229. 

compounds,  229. 
Arsenious  acid,  229. 
Artificial  dyestuffs,  470. 

leather,  524. 

silk,  442. 
Arum,  362. 
Asafoetida,  350. 
Asphalt,  299. 
Asphaltene,  299. 
"  Assistant"  in  dyeing,  482. 
Astatki  as  fuel,  30,  295. 
Attar  of  roses,  339. 
Auxochromous  groups,  480. 
Azo  dyes,  474. 


Bag  filter,  11. 

filter  for  sugar,  380. 
Balance,  Westphal's,  23. 
Balata  (rubber  gum),  348. 
Ball  clay,  181. 

mill,  145. 

Balling  furnace,  74. 
Balsams,  346. 
Balsam  of  Peru,  346. 

of  Tolu,  346. 

Storax,  346. 

Barbier's  tower  system  for  acid,  59. 
Barium  chromate,  206. 

nitrate,  124. 

peroxide,  231. 

sulphocyanide,  250. 
Barkometer,  519. 
Barytes,  197. 
Basic  dyes,  483. 
"  Bating  "  of  skins,  517. 
Baudelot  cooler  for  beer,  401. 
Baume  hydrometer,  22. 
Bayer's  process  for  pure  alumina,  242. 
Beating  engine  for  paper-pulp,  506. 
Bee-hive  coke  oven,  28. 
Beer,  394. 
Beer-fall,  401. 
Beet  sugar,  376. 
Begasse  as  fuel,  25,  372. 
Bengal  isinglass,  351,  528. 
Benzine  distillate  from  petroleum,  291. 
Benzoin,  346. 
Berlin  blue,  200. 
Biscuit  ware  (ceramics) ,  183. 
"Bittern,"  66. 
Bituminous  coal,  25. 
Black-ash,  76. 

furnace,  74. 


Black  glass,  178. 

"Black  iron  liquor,"  259,  263. 

Black  lake,  214. 

pigments,  213. 

Blanket  (on  printing  machines) ,  495. 
Bleaching  powder,  94,  109. 
"Bleach  liquor,"  109. 
Bleaching,  446. 

of  cotton,  446. 

of  hemp,  454. 

of  jute,  454. 

of  silk,  456. 

of  wool,  455. 
Block  printing,  494. 
Blood  as  fertilizer,  138. 
"  Bloom  "  in  mineral  oils,  294. 
Blotting  paper,  512. 
"Blown  oils,"  312. 
"  Blow-ups  "  for  sugar  refining,  379. 
Blue  glass,  177. 

pigments,  198. 
"Bluestone,"  239. 
Blue  vitriol,  239. 
Bock  beer,  404. 
Boetius  furnace  for  glass,  168. 
Boiled  salt,  63. 
"  Boiled  oil,"  308. 
"  Boiled-off  liquor,"  439. 
"Boiled -off"  silk,  439. 
Boiler  scale,  37. 
JBombonnes,  70,  115. 
Bone-ash     as     source    of     phosphorus, 

221. 

Bone-black,  139,  214,  265,  368. 
Bone-char,  139,  265,  368. 
Bone-char  filter,  367. 
Bone  glue,  527. 
Bone-meal,  138. 
Bone  oil,  265. 

Boracite  as  source  of  boric  acid,  226. 
Borax,  226. 
Boric  acid,  225. 

Boussingault's  process  for  oxygen,  234. 
Bowl  (for  printing  machine),  495. 
Brandy,  411. 
Bran  drench,  518. 
Brazil  wood,  468. 

lakes,  212. 
Bremen  blue,  202. 
Brewing,  394. 
Brewing  kettle,  400. 
Bricks,  187. 
Brimstone,  roll,  43. 
Erin's  process  for  oxygen,  234. 
British  gum,  363. 
Bromine,  215. 
Brown  coal,  25. 

pigments,  213. 

powder,  422. 
Brunswick  green,  202. 


INDEX 


531 


Burgundy  pitch,  342. 
"Burning"  (calcining),  16. 
Butter  fat,  318. 
Butteriue,  318. 


Cacao-butter,  316. 

Cadmium  yellow,  207. 

Calceroni,  40. 

Calcination,  16. 

Caliche,  120. 

"  Calorisator  "  for  beet  juice,  376. 

Camphor,  337. 

Camwood,  468. 

Canaigre,  466. 

Candles,  329. 

Cane  sugar,  370. 

Caoutchouc,  346. 

Carbolic  oil,  281,  283. 

Carbon  disulphide,  253. 

tetrachloride,  255. 
Carbonating  tower,  87. 
Carburettor  for  water  gas,  266. 
Carmichaei's  electrolytic  apparatus,  106. 
Carmine,  212. 
Carnallite,  134. 

Cast-iron  still  for  sulphuric  acid,  58. 
Castner's  electrolytic  apparatus,  107. 
"Catch-all,"  6,  7. 
Catechu,  464. 
Caustic  potash,  136. 

soda,  80,  90. 
Cement,  148,  152. 
Centre-bit,  287. 
Centrifugal  machine,  14. 

sugars,  374. 

Ceramic  industries,  180. 
Ceresine,  299. 
Chamber  acid,  45. 
"  Chamber  crystals,"  47. 
Chamber  process  for  white  lead,  192. 
Chamois  leather,  520. 
Champagne,  393. 
Chance-Glaus  process  for  the  treatment 

of  tank  waste,  84. 
"  Chaptalized  "  wine,  392. 
Charcoal,  26. 

as  pigment,  214. 

"  Cheese-box  "  still  for  petroleum,  391. 
Chemical  pulp,  502. 
Chemical  theory  of  dyeing,  480. 

of  tanning,  524. 
"  Chemick,"  447. 
Chestnut  extract,  465. 
Chili  saltpetre,  119. 
China  clay,  180. 

as  pigment,  198. 
China  grass,  437. 
Chinese  blue,  200. 


Chinese  red,  210. 

vermilion,  211. 

wax,  320. 

white,  197. 
Chip  casks,  402. 
Chlorates,  111. 
"Chloride  of  lime, "94. 
Chlorine  industry,  94. 

still,  earthenware,  95. 

still,  sandstone,  95. 
Chondrin,  in  glue,  525. 
Chrome  alum,  146. 

green,  203, 493. 

orange,  206,  208,  493. 

red,  206,  209. 

tannage,  521. 

yellow,  205. 

yellow  as  dye,  493. 
Chromium  salts  as  mordants,  458. 
Chromogens,  479. 
Chromophores,  479. 
Cider,  393. 

vinegar,  414. 

Clark's  process  of  water  purification,  36. 
Glaus  kiln,  85. 
Close  roaster,  68. 
Closed  pots  for  glass,  170. 
Coal  gas,  268. 
Coal-tar,  278. 

distillation,  280. 

dyestuffs,  471. 
Cobalt  blue,  202. 
Cochineal,  469. 

lake,  212. 

Cocoa  powder,  422. 
Cocoanut  fibre,  437. 
Coffey  still,  9. 
Coke,  27. 
Coke  tower,  70. 
Colcothar,  210. 
"Cold  test"  for  oils,  297. 
Collagen,  in  skins,  514. 
Cologne  spirit,  408. 
Colophony,  341. 
Color  mixing,  496. 

pans,  496. 
Colored  glass,  176. 

leather,  520. 

Combination  tannage,  521. 
Compound  glass,  176. 
"Compound  lard,"  317. 
Compression    machines    (refrigeration), 

20. 

"  Concentrated  "  alum,  242. 
Concrete  sugars,  374. 
Condenser  for  gas-making,  270. 
"  Conditioning  "  of  silk,  439. 

of  wool,  443. 
"  Condy's  liquid,"  255. 
Copal,  343. 


532 


INDEX 


Copperas,  237. 
Copper  greens,  204. 

salts  as  mordants,  461. 

sulphate,  239. 
Cordite,  430,  431. 
Coriin,  in  skin,  514. 
Cornish  stone,  186. 
Cotton,  434. 

bleaching,  446. 

dyeing,  with  acid  dyes,  485. 

dyeing,  with  aniline  black,  491. 

dyeing,  with  basic  dyes,  484. 

dyeing,  with  direct  dyes,  483. 

dyeing,  with  indigo,  489. 

dyeing,  with  ingrain  azo  dyes,  492. 

dyeing,  with  mordant  dyes,  486. 

"mercerized,"  435. 
Cotton-seed  oil,  310. 

stearin,  311. 
.Coupler's  still,  8. 

"  Crabbing  "  of  mixed  wool  goods,  455. 
"  Cracking  "  of  crude  petroleum,  292. 
"  Crazing  "  of  pottery,  187. 
Cream  of  tartar,  391. 
Creosote  oil,  from  wood-tar,  264. 

from  coal-tar,  283,  281. 
"  Crown  filler,"  198. 
Crown  glass,  175. 
Crude  petroleum  as  fuel,  30. 
Crutcher,  for  soap,  325. 
Crystals,  15. 
Crystal  meal,  15. 
Crystallization,  15. 
Cryolite  soda  process,  92. 
Cudbear,  469. 
Curcuma,  362,  470. 
Currying,  520. 
Cut  glass,  175. 
Cutch,  464. 
Cyanides,  247. 
"Cyan-salt,"  251. 
Cylinder  machine  for  paper,  511. 
Cylinder  oil,  295. 


Dammar,  343. 

Date  palm  sugar,  371. 

Deacon  process  for  chlorine,  98. 

Decoction  method  of  mashing,  399. 

Deep  rooms  (for  salt  making),  62. 

Defecation  of  sugar  beet  juice,  373. 

of  sugar  cane  juice,  377. 
Degras,  523,  524. 

Dejardin's  sulphur  apparatus,  42. 
Density,  21. 
Dephlegmator,  8. 

Depilation  process  (in  tanning),  516. 
Destructive  distillation  of  bones,  265. 

of  wood,  257. 
Detonation,  417. 


Deville's  process  for  oxygen,  234. 
Devitrification  of  glass,  165. 
Devulcanizatiou  of  rubber,  349. 
Dextrin,  363. 
Dextrine,  363. 
Dextrose,  364,  369. 
Dietsch  cement  kiln,  156. 
Diffusion  process  for  sugar  beets,  376. 

for  sugar  cane,  373. 
Digesters  for  sulphite  pulp,  504. 
"  Dippel's  oil,"  265. 
Direct  dyes,  482. 

Direct  specific  gravity  hydrometer,  21. 
"Discharge"  (in  textile  printing),  497. 
Discharge  style  (in  textile  printing) ,  498. 
Discharging  of  silk,  439. 
Distance  frame  (of  filter  press),  12. 
Dolly,  for  cloth  scouring,  455. 
Donald's  process  for  chlorine,  101. 
Dongola  process  for  leather,  521. 
Down-draught  kilns,  184. 
Dragon's  blood,  343. 
Dressed  leather,  520. 
"Driers  "  for  boiled  oil,  309. 
"  Drips,"  for  sulphuric  acid,  53. 
Drying  of  oils,  303. 
Dunlop's   method    for    the  recovery  of 

manganese  oxides,  96. 
Dunlop's  nitric  acid-chlorine  process,  101. 
Durgen  system  of  preparing  corn  starch, 

355. 
Dutch  process  for  vermilion,  211. 

for  white  lead,  190. 
Dyeing,  497. 

Dyeing  style  (textile  printing),  498. 
Dynamite,  428. 


Eau  de  Javelle,  109. 

Eau  de  Labarraque,  109. 

Ebonite,  349. 

Edge-runner,  304. 

Elaidin  test  of  oils,  307. 

Electrolysis  of  brine,  104. 

Electrolytic    processes    for   white   lead, 

195. 

Elemi,  345. 

Emerald  green  (pigment),  205. 
Enamel,  178,  186. 
Encaustic  tiles,  185. 
Enfleurage,  335,  336. 
Engobe  (glaze),  186. 
Enzymes,  384. 
Eosins,  473. 
Epsom  salts,  134. 
Esparto,  437, -508. 
Essential  oils,  335. 
Etageofen,  156. 
Ethiops  mineral,  211. 
Euphorbium,  350. 


INDEX 


533 


Evaporation,  3. 

"Even  motion  coating"  (rubber  cloth), 

349. 
Exhauster  for  gas,  Beale's,  271. 

steam-jet,  272. 
Explosives,  417. 
"  Extract "  in  beer,  403. 
Extraction,  2. 

Extraction  process  for  oils,  305. 
Extracts  (tannin),  466. 


Faience,  185. 

"  Fat  clay,"  181. 

"  Fat  lime,"  148. 

Fatty  oils,  301. 

Feldmann's  ammonia  apparatus,  125. 

Fermentation,  384. 

bottom,  31)0,  402. 

top,  390,  403. 

Fermentation  industries,  384. 
Ferments,  384. 
Ferric  nitrate,  122. 
Ferrous  nitrate,  122. 

sulphate,  237. 
Fertilizers,  137. 
Fibres,  433. 

animal,  438. 

vegetable,  434. 
Fibroine  of  silk,  438. 
Filter  press,  12. 
Filtration,  11. 
Fire-brick,  188. 
Fire-clay,  180. 
"  Fire-test "  for  oils,  296. 
''  Firing  "  (calcining),  16. 
"  First  sugar,"  374. 
Fish  glue,  527. 

scrap,  140. 

Flash  point  of  oils,  295. 
Flax,  435. 

"  Floaters  "  in  glass  furnace,  169. 
Flowers  of  sulphur,  43. 
Forcite,  430. 

Fourdrinier  machine,  511. 
Fractional  condensation,  8. 
Frankincense,  351. 

French  column  apparatus    for  distilla- 
tion, 9. 

French  process  for  white  lead,  193. 
"Friction  coating"  (rubber  cloth),  349. 
Fuels,  24. 

gaseous,  30. 

liquid,  30. 

solid,  24. 
Fulminates,  431. 
Fumeroles,  225. 
Fuming  acid,  nitric,  118. 

sulphuric,  45,  60. 


Furnace,  annealing,  173. 

"balling"  (black-ash),  74. 

flattening,  174. 

glass,  168. 

muffle,  16. 

reverberatory,  17. 

revolving,  17,  75. 

shaft,  18. 

tank,  169. 
"  Furnisher,"  495. 
Fusel  oil,  408,  410. 
Fustic,  470. 


Galbanum,  350. 

Gall    and    Montlaur    process   for   chlo- 
rates, 113. 

Gal  land  process  for  malt,  396. 
"Gallized"  wine,  392. 
Gall-nuts,  464. 
Galls,  464. 
Gambier,  464. 
Gamboge,  208,  351. 
Garbage  as  fertilizer,  139. 
Gas,  analyses  of,  278. 

coal,  as  fuel,  30. 

fuel,  30. 

illuminating,  265. 

natural,  30. 

producer,  30. 

water,  as  fuel,  33. 

water,  as  illuminant,  266. 
Gas  producer,  Siemens',  31. 

Taylor's,  31. 
Gay-Lussac  tower,  54. 
Gelatine,  525,  527. 

dynamite,  430. 
Gelis'  process    for    ammonium   sulpho- 

cyanide,  248. 
German    (chamber)    process   for  white 

lead,  192. 

Gerstenhofer  furnace  (pyrites),  51. 
Giant  powder,  429. 
Gin,  411. 
Glass.  165. 

gall,  172. 

stills  for  sulphuric  acid,  56. 
Glass-making  process,  171. 
Glatz  process  for  glycerine,  333. 
Glauber's  salt,  72,  135. 
Glazes,  186. 
Glazed  tiles,  186. 
Glover  tower,  52. 
Glucose,  363,  364,  369. 

converter,  365. 
Glucosides,  364. 
Glue,  525. 
Glutin,  525. 
Glycerides  in  oils,  301. 


534 


INDEX 


Glycerine,  332. 

chemically  pure,  333. 

crude,  333. 

dynamite,  332. 

from  soap  lyes,  332. 
Grainers  for  salt,  65. 
"  Graining  "  of  morocco  leather,  523. 
Granulator  for  sugar,  381. 
Grape  sugar,  364,  367. 
Graphite  as  pigment,  214. 
Green  glass,  176. 
"  Green  oil,"  281,  284. 
Green  pigments,  202. 
"  Green  starch,"  357. 
Green  malt,  395. 

vitriol,  237. 

Greenwood's  electrolytic  apparatus,  106. 
Griffin  mill,  159. 
"Grog, "181. 

Griineberg-Blum  ammonia  still,  126. 
Guaiacum,  344. 
Guano,  140. 
Guignet's  green,  203. 
Gum,  acacia,  351. 

animi,  343. 

Arabic,  351. 

juniper,  342. 

Senegal,  351. 

tragacanth,  351. 
Gum-resins,  350. 
Gun-cotton,  423. 
Gunpowder,  418. 
Gutta-percha,  350. 

Guttmann's  nitric  acid  apparatus,  116. 
Gypsum,  197. 


Hand  frame  for  paper  making,  511. 
"Handling"  of  hides  in  the  "soaks," 

515. 

Handlers  for  hides  while  tanning,  519. 
Hard  porcelain,  183. 

rubber,  349. 

water,  35. 
Hardness,  temporary  (of  water),  35. 

permanent  (of  water),  35. 
Hargreaves  process,  71. 
Hargreaves-Bird  electrolytic  process,  107. 
Hart's  nitric  acid  apparatus,  117. 
Hasenclever-Helbig  pyrites  burner,  52. 
Hemlock  bark,  465. 
Hemp,  436. 

bleaching,  454. 

Herseus'  gold-lined  acid  still,  57. 
Hermite  electrolytic  process,  107. 

bleaching  process,  453. 
Hide  glue,  525. 
Hides,  515. 
Hoffmann's  cement  furnace,  157,  184. 


Holland-Richardson  electrolytic  process, 

106. 

"  Hollander  "  (pulp  machine) ,  506. 
Hop-back,  401. 
Hops,  400. 

Horizontal  still  fcr  petroleum  distilla- 
tion, 291. 
Hydraulic  lime,  150,  153. 

main,  270. 

press,  305. 

Hydrochloric  acid,  67. 
Hydrogen  peroxide,  232,  453,  456. 
Hydrolysis  of  oils,  303. 
Hydrometer,  Baume's,  22. 

direct  specific  gravity,  21. 

Twaddell's,  22. 
Hypochlorites,  108. 
Hyposulphurous  acid,  44. 


Iceland  moss,  351. 
Illuminating  gas,  265. 
Indian  red,  210. 

yellow,  208. 
Indigo,  202,  466. 

carmine,  467. 
"Indigo  salt,"  479. 
"  Indigotine,"  467. 
Indulines,  472. 
Indurite,  431. 

Infusion  method  of  mashing, 
"  Ingrain  colors,"  477. 
Iodine,  218. 

value  of  oils,  306. 
Iridescent  glass,  178. 
Irish  moss,  352. 
Iron  alum,  246. 

buff,  460,  493. 

salts  as  mordants,  460. 
Isinglass,  528. 
Ivory  black,  214. 


"  Jaggary  "  sugar,  371. 
Japan  wax,  317. 
"Jars,"  288. 
"  Jigger,"  482. 
Jute,  437,  509. 
bleaching,  454. 


Kainite,  135. 

Kaolin  (kaolinite),  180. 

as  pigment,  198. 
Kauri,  343. 
Kemp,  443. 
Keratine,  443. 
Kermes,  469. 
Kerosene,  distillate  from  petroleum,  291. 


INDEX 


535 


Kettle  process  for  salt,  63. 

Kier  for  cotton  bleaching,  449. 

Kilns,  18,  148,  149. 

Kino,  465. 

Kips,  515. 

Koechlin's  bleaching  process,  452. 

Krenmitz  process  for  white  lead,  194. 

Kumis,  393. 


Lac,  344. 

Lac-dye,  344,  469. 

Lactic  acid,  415. 

Laevulose,  364. 

Lager  beer,  404. 

"Laid"  paper,  512. 

"Lakes,  "212. 

Lanolin,  320. 

Lant  for  wool  scouring,  446. 

Lard,  317. 

oil,  315. 

"  Layers  "  for  tanning  hides,  519. 
Lead  acetate,  263. 

chromate,  205. 

nitrate,  122. . 
"Lead  plaster,"  328. 
Lead  sulphite,  196. 

burning,  53. 

chambers,  52. 

glass,  166. 

pans,  56. 
Leather,  514. 
Leblanc  soda  process,  73. 
Le  Sueur's  electrolytic  process,  105. 
Levigation,  2. 

Liebig's  chlorate  process,  111. 
Light  oil  from  wood-tar,  264. 

from  coal-tar,  282. 
Lignite,  25. 
Lima  wood,  468. 
Lime,  148. 

boil  in  bleaching,  449. 

cartridges,  432. 

glass,  166. 
Limekilns,  148. 
"Lime  rooms,"  63. 
Liming  of  skins,  516. 
Linde  refrigeration  process  for  oxygen, 

236. 

Linen  bleaching,  453. 
Linseed  oil  varnish,  345. 
Liqueur,  393,  411. 
Liquid  fuels,  30. 

glue,  527. 
Litharge,  207. 
Litmus,  469. 
Lixiviation,  2. 
Loaf  sugar,  383. 

Loewig's  process  for  caustic  soda,  81. 
Logwood,  467. 


"Long  flame  burning,"  18. 
"Low  wines,"  410. 
Lucifer  matches,  224. 
Lunge  plate,  58,  70. 
Lye-boils  in  bleaching,  450. 


M 


Machine  printing,  495. 
Mactear's  furnace,  69. 
Madder,  468. 

bleach  for  cotton,  448. 

lake,  212. 

style  (textile  printing) ,  498. 
Majolica,  185. 

Malachite  green  (pigment) ,  204. 
Maletra  pyrites  burner,  50. 
Maltha,  299. 
Malting,  394. 
Manganates,  255. 
Manganese  brown,  494. 
Manilla  hemp,  437. 
Maple  sugar,  371. 
Market  bleach,  451. 
Martin's  process  for  wheat  starch,  358. 
Mashing,  397. 
Masse-cuite,  374. 
Massicot,  208,  209. 
Mastic,  342. 
Matches,  224. 

Mather-Thompson  bleaching  process,  452. 
Maumene  test  of  oils,  307. 
Mechanical  theory  of  dyeing,  480. 

of  tanning,  524. 
Mechanical  wood  pulp,  502. 
Melinite,  431. 

Melter  for  sugar  refining,  379. 
Menthol,  338. 
Methyl  alcohol,  259. 
Methylated  spirit,  409. 
Mica  powder,  429. 
Milk  glass,  177. 

Milner's  process  for  white  lead,  194. 
Mimosa  bark,  465. 
Mineral  dyes,  492. 

green,  204. 

oils,  285. 

phosphates  as  source  of  phosphorus, 
222. 

white,  197. 
Mirrors,  178. 
Mond's  process  for  chlorine,  103. 

for  treating  tank  waste,  83. 
Mordants,  457. 
Mordant  dyes,  486. 
Morocco  leather,  523. 
Mortar,  151. 
Mother-liquor,  15. 
Moulds,  385. 


536 


INDEX 


Mountain  blue,  202. 

green,  204. 
Muffle  furnace,  16. 

roaster,  68. 
Muga  silk,  441. 

Multiple  effect  system  of  evaporation,  6. 
Muriatic  acid,  67. 
Muriate  of  tin,  461. 
Muscovado  sugar,  374. 
Musk,  artificial,  343. 
Must,  390. 
Myrabolans,  465. 
Myrrh,  351. 

N 

Naphthalene,  284. 
Natural  dyestuffs,  466. 

gas,  30. 

Neutral  alum,  246. 
"  Neutral  oils,"  294. 
Neutralizer  for  glucose,  366. 
New  wine,  391. 
"Nigre"  of  soap,  325. 
Nigrosines,  472. 
Nitrates,  119. 
Nitrate  of  iron,  123,  460. 
Nitre  cake,  55. 

pot,  50. 

Nitric  acid,  114. 

Nitric  acid-chlorine  processes,  101. 
Nitrocellulose,  423. 
Nitro  dyes,  473. 
Nitrogelatine,  430. 
Nitroglycerine,  425. 
Nitrogenous  waste  as  fertilizer,  139. 
Nitroso  dyes,  473. 
Nitrosulphonic  acid,  47. 
"Nitrous  vitriol,"  54. 
Nitrosylsulphuric  acid,  46,  47. 
Non-porous  ware  (in  ceramics),  182. 
Nordhausen  sulphuric  acid,  45. 
Normal  needle  for  cement  tests,  161. 
Nut-galls,  464. 


Oak  bark,  465. 

Oil,  almond  (essential), 

bergamot,  338. 

blackfish,  315. 

blubber,  315. 

cajaput,  338. 

cassia,  338. 

castor,  312. 

cedar,  338. 

chamomile,  338. 

cinnamon,  338. 

clove,  338. 

cocoanut,  316. 

cod-liver,  314. 


Oil,  colza,  311. 

corn,  310. 

cotton-seed,  310. 

earthnut,  313. 

eucalyptus,  339. 

fish,  314. 

geranium,  339. 

Gingili,  311. 

hemp,  310. 

lard,  315. 

lavender,  339. 

lemon,  339. 

linseed,  308. 

liver,  314. 

menhaden,  314. 

mustard,  339. 

neat's-foot,  315. 

"oleo,"316. 

olive,  313. 

origanum,  340. 

palm,  316. 

palm-nut,  316. 

peanut,  313. 

peppermint,  339. 

pogy,  314. 

poppy,  310. 

porpoise,  315. 

rape-seed,  311. 

rose,  339. 

rue,  340. 

sassafras,  340. 

sesame,  311. 

shark-liver,  314. 

sperm,  318. 

sunflower,  310. 

tallow,  316. 

thyme,  340. 

train,  315. 

turpentine,  336. 

whale,  315. 

wintergreen,  340. 

wormwood,  340. 
Oil  gas,  276. 
Oil  of  vitriol,  45,  57. 
Oil  tannage,  522. 
Oil  tester,  closed  (Abel's),  296. 

open,  296. 
Oil  well  drilling,  287. 

torpedoing,  289. 
Oils,  drying,  308. 

non-drying,  313. 

marine  animal,  314. 

semi-drying,  310. 

terrestrial  animal,  315. 
Olein,  303,  330,  331. 
Oleo-resins,  346. 
Olibanum,  351. 
Opal  glass,  177. 
Open  pots  for  glass,  170. 

roaster,  67. 


INDEX 


537 


Orange  glass,  177. 

mineral,  208. 

pigments,  208. 
Origanum,  340. 

Orleans  process  for  vinegar,  412. 
Orpiment,  201. 
Orseille,  469. 

Otto-Hoffmann  coke  oven,  28. 
"  Overchromed  "  wool,  459. 
Oxidation     style      (textile      printing), 

498. 

Oxazines,  472. 
Oxyazo  dyes,  475. 
Oxygen,  233. 
Ozokerite,  298. 


Padding  machine,  482. 
Palmitin,  303. 
Panclastite,  432. 
Pan  process  for  salt,  65. 
Paper,  501. 

Paper-making  process,  509. 
Paraffine  oils,  294. 
Parchment,  524. 

paper,  513. 
Paris  green,  205. 

white,  198. 

Parke's  process  of  vulcanizing,  348. 
Parnell-Simpson   process    for    utilizing 

tank  waste,  90. 
"  Pasteurizing"  of  wine,  392. 
Patent  leather,  520,  523. 
Pattinson's  white  lead,  196. 
Pauli's  process  for  purifying  tank  liquor, 

78. 

Peach  wood,  468. 
Pearlash,  130. 
"  Pearl  hardening,"  198. 
Pearl  sago,  361. 
Peat,  25. 

Pebble  powder,  421. 
Permanent  hardness  in  water,  35. 
Permanganates,  255. 
Pernambuco  wood,  468. 
Peroxides,  231. 
Perret-Ollivier  burner,  51. 
Persian  berries,  470. 
Petrolene  in  asphalt,  299. 
Petroleum,  crude,  290. 

industry,  285. 

refining,  290. 

refining  of  sulphur  bearing,  294. 
Phenol  (carbolic  acid),  283. 

dyes,  473. 

Phosphate  rock,  140. 
Phosphatic  slag,  145. 
Phosphorites,  141. 
Phosphorus.  221. 


Phthale'ins,  473. 

Physical  theory  of  tanning,  524. 

Picrates,  431. 

Pigments,  189. 

Pigment  style  (textile  printing),  497. 

Pipe  clay,  181. 

Pipe-column,  59. 

Pitch  from  coal-tar,  285. 

"  Pitching  "  of  wort,  401. 

Plaster  of  Paris,  163. 

Plate  glass,  173. 

tower  (Lunge's),  58,  70. 
Platinum  stills,  56. 
"  Plumping  "  of  hide,  516,  517. 
Pneumatic  malting,  396. 
Porcelain,  182. 

Porous  ware  (in  ceramics) ,  182, 185. 
Porter,  404. 
Portland  cement,  155. 
Potash  industry,  130. 
Pot  furnace  for  glass,  168. 
Pots  for  glass,  170. 
Potassium  alum,  246. 

bichromate,  136. 

bromide,  217. 

carbonate,  135. 

chlorate,  111. 

cyanide,  251. 

ferricyanide,  250. 

f^rrocyanide,  249. 

manganate,  255. 

nitrate,  120. 

permanganate,  255. 

silicate,  231. 

sulphate,  135. 
Potato  starch,  359. 
Pozzuolanic  cements,  153. 
Press-cakes  from  oil  industry  as  fertil- 
izer, 139. 

Pressed  glass,  175. 
Prismatic  powder,  421. 
Producer  gas,  30. 
Proof  stick,  381. 
Prussian  blue,  200. 

as  dye,  493. 

"  Puering  "  of  skins,  517. 
Pulk6,  393. 
"  Pulled  wool,"  442. 
Purifiers  for  gas,  273. 
Purification  of  water,  36. 
Purpurin,  468. 
Purree,  208. 

"  Putrid  soak  "  (for  dried  hides),  515. 
Pyknometer,  23. 
Pyrites,  48. 

burners,  49. 

"  smalls,"  49. 
Pyroligneous  acid,  257. 
Pyrolignite  of  iron,  259,  263. 
Pyroxyline,  425. 


538 


INDEX 


Q 

Quebracho,  465. 

Quercitron,  470. 

Quick-cook  sulphite  process,  505. 

Quick  vinegar  process,  413. 

Quinoline,  derivatives,  477. 


Rabble,  69. 

Rack-a-rock,  432. 

Rags  as  paper  stock,  508. 

Ramie,  437. 

Rational  analyses  of  clays,  182. 

Realgar,  212. 

"  Reclaimed  "  rubber,  349. 

Rectifier,  9. 

Red  glass,  177. 

lead,  209. 

ochre,  210: 

pigments,  209. 

phosphorus,  223. 

prussiate  of  potash,  250. 

woods,  468. 
"Red  oil, "330. 
"  Reduced  oil,"  293,  295. 
Refined  pearlash,  131. 
Refining  of  glass,  172. 
Refrigeration,  18. 

Regenerative  furnace  (Siemens'),  32. 
Rendering  of  fats  by  steam,  305. 
Rendering  tank,  306. 
Resins,  341. 
"Resist,"  497. 

Resist  style  (textile  printing) ,  499. 
Retorts  for  wood  distillation,  258. 
Retting  of  flax,  436. 
Reversion  of  superphosphates,  144. 
Revivifying  of  bone-char,  369. 
"  Ricks  "  for  brine  evaporation,  3. 
"Roasting"  (calcination),  16. 
Roburite,  432.- 
Rock  salt,  61. 
Roller  printing,  495. 
Roman  alum,  245. 

cements,  154. 
Romite,  432. 
Rosaniline  dyes,  471. 
Rosendale  cement,  154. 
Rosin,  341. 
Rosin  change  in  soap  boiling,  325. 

grease,  342. 

oil,  342. 

soap,  323. 

spirit,  341. 
Rosolic  acids,  474. 
Rotary  furnaces,  4,  17,  158. 
"Rotting  process"  for   potato    starch, 

360. 
Rouge,  210. 


Rubber,  346. 

cements,  349. 

compounding,  347. 

substitutes,  348. 
Rum,  411. 

Russian  leather,  523. 
Russian  petroleum,  295. 

S 

Sadler- Wilson  chlorine  process,  101. 

Safety  matches,  224. 

Safranines,  472. 

Sago,  361. 

Sago  flour,  361. 

Saladin  system  of  malting,  397. 

Sal-soda,  79. 

Salt,  61. 

Salt-cake,  72. 

furnace,  67. 

"  Salt  water  "  in  glass  furnace,  172. 
Saltpetre,  120. 
Sandalwood,  468. 
Sandarac,  342. 
Sand  filter,  15. 
"  Sanitas,"  337. 
Saponification,  303,  321. 

by  heating  with  water,  330. 

by  lime,  330. 

by  Milly's  process,  330. 

by  sulphuric  acid,  331. 

value,  306. 
Sappan  wood,  468. 
Schaffner-Helbig    process    for   treating 

tank  waste,  84. 
"  Scheelizing  "  of  wine,  392. 
Scheele's  green,  204. 
Schlempe,  131. 

Schlossing  process  for  chlorine,  97. 
Scrubber,  272. 
Scrubber-washer,  273. 
Sea-salt,  61. 
Sea-silk,  441. 
"  Second  light  oil,"  281. 
"  Second  sugar,"  374. 
Semet-Solvay  coke  oven,  29. 
"Seneca  oil,"  287. 
Separator,  6. 
Sepia,  213. 
Sericine,  438. 
Sewage  as  fertilizer,  147. 
Shaft  furnaces,  18. 
Shale  oil  industry,  298. 
Shanks'  process  of  lixiviation,  76. 
Shellac,  344. 

"  Shivering  "  of  pottery,  187. 
"  Short  flame  burning,"  18. 
Siemens'  gas  producer,  31. 

regenerative  furnace,  32. 
Sienna,  207. 


INDEX 


539 


Silent  spirit,  409. 
Silk,  438. 

bleaching,  457. 

"  boiled  off,"  439. 

dyeing,  483,  484,  486,  489. 

ecru,  440. 

glue,  438. 

souple',  440. 

tussur,  441. 
Silver  nitrate,  123. 
Simon-Carve's  coke  oven,  29. 
"  Singeing  "  of  cotton  cloth,  448. 
Sisal,  437. 

Sizing  of  paper,  510. 
"  Skipping  "  of  sugar,  381. 
Skins,  515. 
"  Skivers,"  520. 
Slabber  machine  for  soap,  326. 
Slag  cement,  153. 

fertilizers,  145. 
"  Slip  "  (prepared  clay),  182. 
Slow-cook  sulphite  process,  505. 
Smalt,  201. 

Smokeless  powder,  425,  430. 
Soap,  321. 

Castile,  322. 

"boiled  down, "326. 

"cold  process, "323,  324. 

laundry,  323. 

milled,  328. 

mottled,  323,  327. 

remelted,  328. 

soft,  322. 

toilet,  323,  327. 

transparent,  328. 
Soap  boiling,  324. 

frames,  326. 

kettles,  323. 
"  Sod-oil,"  523. 
Soda-ash,  89. 
Soda  crystals,  79. 

industry,  73. 

process  for  wood  pulp,  502. 
Sodium  alum,  246. 

acetate,  263. 

arsenate,  230. 

arsenite,  230. 

bisulphite,  44. 

bromide,  218. 

chlorate,  112. 

hyposulphite,  44. 

manganate,  255. 

nitrate,  119. 

peroxide,  233. 

sulphate,  72. 

thiosulphate,  45. 
Soffioni,  225. 
Soft  sugars,  382. 

porcelain,  183. 
Sole  leather,  519. 


Solar  salt,  62. 

"  Solidified  "  bromine,  217. 

Solid  solution  theory  of  dyeing,  480. 

Solvent  naphtha  from  coal-tar,  282. 

"Souring,  "447, 450. 

Sour  process  for  wheat  starch,  358. 

Spanish  grass,  508. 

"  Sparger,"  400. 

Spence's  burner,  51. 

Spent  tan-bark  as  fuel,  25. 

Spermaceti,  319. 

Spindle  oils,  295. 

Spirits  of  turpentine,  336. 

Spirit  varnishes,  345. 

Splitting  of  skins,  520. 

Spraying,  petroleum  oils,  293. 

Sprengel  explosives,  432. 

"  Spueing  "  of  leather,  515. 

Staking  of  skins,  521. 

Starch,  353. 

cassava,  362. 

corn,  354. 

potato,  359. 

rice,  360. 

sago,  361. 

wheat,  358. 
Stassfurt  salts,  132. 
Steam  style  (textile  printing) ,  497. 
Stearin,  303. 
Stearine,  330. 
Stick  lac,  344. 
Still,  Coffey,  9. 

Coupler's,  8. 

French  column,  9. 
Stockholm  tar,  264. 
Stoneware,  184. 
Stout,  404. 
"Stoving"     of     wool     in     bleaching, 

456. 

"  Strike  pan  "  for  sugar,  374. 
Strontium  nitrate,  124. 

process  for  recovery  of  sugar  from 

beet  molasses,  377. 
"  Stuffing  "  in  leather,  520. 
"Stuffing  and  saddening"  (in  dyeing), 

486. 

Style  (in  textile  printing) ,  497. 
Sublimation,  10. 
Sublimed  white  lead,  196. 
Sucrose,  370. 
"  Sugar  of  lead,"  263. 
Sugar    recovery    from    beet    molasses, 

377. 

Sugar  refining,  378. 
Suint,  131,  320,  444. 
Sulphates,  237. 

Sulphate  process  for  wood  pulp,  506. 
Sulphite  process  for  wood  pulp,  503. 
Sulphite  digester,  504. 
Sulphur,  39. 


540 


INDEX 


Sulphur  dioxide,  43. 

purification,  42. 

recovered,  42. 
Sulphuric  acid,  45. 
Sumach,  464. 
Superphosphates,  143. 
Suspenders  for  tanning  hides,  519. 
"  Sweating  "  of  hides,  517. 
"  Sweet  waters  "  (glycerine),  332. 

(glucose) ,  368. 


Tallow,  317. 

bone,  318. 
Tankage,  139. 
Tank  furnace  for  glass,  169. 

liquor,  77. 

waste,  76,  82. 
Tanning  processes,  518. 
Tanning  with  oils,  522. 
Tannins,  463. 
Tapioca,  362. 

Tar  stills  for  petroleum  residuum,  293. 
Tawing  of  skins,  521. 
Taylor's  gas  producer,  31. 
Tempered  glass,  175. 
"  Tempering"  of  bone-char,  367. 
Temporary  hardness  in  water,  35. 
Terra  alba,  197. 

cotta,  187. 

verde,  205. 

Tessie  du  Motay  process  for  oxygen,  235. 
Testing  of  cement,  160. 
Textile  industries,  433. 

printing,  494. 
Thelen'span,  79,  89. 
Thenard's  process  for  white  lead,  193. 
Thionines,  473. 
Thymol,  337. 
Tiles,  185. 

Time  of  setting  of  cement,  161. 
Tin  salts  as  mordants,  461. 
"Tin  spirits,"  461. 
Tinkal,  227. 
Tissue  paper,  512. 
Tough  glass,  175. 
Tragacanth,  351. 

"  Trying  out"  of  animal  fats,  305. 
Turkey-red  oil,  312. 
bleach,  451. 
dyeing  process,  487. 
Turmeric,  470. 
Turnbull's  blue,  201. 
Turpentine  varnish,  345. 
Twaddell's  hydrometer,  22. 


Udells,  218. 
Ultramarine  blue,  198. 
green,  199,  202. 


Ultramarine  red,  200. 

violet,  200. 
Umber,  213. 

Ungumming  of  silk,  439. 
Unhairing  process  (in  tanning) ,  516. 
Up-draught  kiln,  184. 
Upper  leather,  520. 

V 

Valonia,  465. 
Vandyke  brown,  213. 
Van  Ruymbeke  process  for  glycerine,  332. 
Varec  as  source  of  iodine,  218. 
Varnish,  345. 
Vaseline,  295. 
Vegetable  drying  oils,  308. 

tannage,  518. 
Vellum,  524. 
Venetian  red,  210. 
Vermilion,  210. 
Vermilionettes,  211. 
Verdigris,  204. 
Vinasse,  131. 
Vinegar,  412. 
"  Vinegar  mother,"  412. 
Violet  glass,  177. 
Viscosity  test  for  oils,  297. 
Vitrified  tiles,  185. 
Vitriol,  oil  of,  45. 

blue,  239. 

green,  237. 

white,  240. 

Vulcanization  of  rubber,  348. 
Vulcanite,  349. 

W 

Washing  machine  for  cotton,  447. 
Wash  leather,  520. 
Water,  hard,  35. 

purification  of,  36. 

saline,  35. 

soft,  35. 

sources  of,  34. 
Water  gas,  266. 

Lowe  process,  266. 

Wilkinson  process,  268. 

as  fuel,  33. 
Water-glass,  230. 
Water-marks  in  paper,  512. 
Wax,  bee's,  319. 

carnauba,  320. 

Chinese,  320. 

insect,  320. 

Japan,  317. 
Waxes,  liquid,  318. 

solid,  319. 

Wedgwood  ware,  184. 
Weiss-bier,  404. 

Weldon  process  for  manganese  recovery 
in  chlorine  making,  96. 


INDEX 


541 


Weldon-Pechiney  chlorine  process,  102. 
"  Weldon  mud,"  97. 
Westphal's  balance,  23. 
Whiskey,  408,  410. 
White  arsenic,  229. 

glass,  177. 

lead,  190. 

pigments,  190. 

vitriol,  240. 

zinc,  197. 
Whiting,  198. 
Willisden  paper,  513. 
Window  glass,  174. 
Wine,  389. 

artificial,  392. 

currant,  393. 

palm,  393. 
Wood  as  fuel,  24. 

pulp,  502. 

spirit,  259. 
Wood-tar,  203. 
Wool,  442. 

bleaching,  455. 

dyeing,  483,  484,  485,  488,  490. 

grease,  320,  444. 

scouring,  444. 
Wort,  399. 


Wove  paper,  512. 
Wrapping  paper,  512. 
Writing  paper,  512. 


Yamamai  silk,  ^41. 
Yaryan  evaporator,  6. 
Yeasts,  386. 

bottom,  387. 

compressed,  388. 

top,  387. 

"wild,"  388. 
Yellow  glass,  176. 

lake,  213. 

ochre,  207. 

pigments,  205. 

phosphorus,  223. 

prussiate  of  potash,  249. 
"  Yellow  liquors,"  83. 
Yorkshire  grease,  445. 
Young  fustic,  470. 


Zinc  chromate,  206. 
sulphate,  240. 
sulphide,  197. 


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